IO. I 3 U August 7.987 A The ‘Response of ‘Honey JVIesquite t0 ‘Herbicide? I9 f THE TEXAS AGRICULTURAL EXPERIMENT STATION Neville . arke, Director, College Station, Texas THE AS A&M UNIVERSITY SYSTEM 1"‘ ‘w; CONTENTS SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 HISTORICAL REVIEW . . . . . . . . . . . . . . . . . . . . . . . 2 Early Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Factors Afiecting Results . . . . . . . . . . . . . . . . . . . . 2 Soil Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Herbicide Mixtures . . . . . . . . . . . . . . . . . . . . . . . . 3 Influence of Soil Temperature . . . . . . . . . . . . . . . 3 Influence of Other Variables . . . . . . . . . . . . . . . . . 3 New Herbicides . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 FACTORS AFFECTING HERBICIDE RESPONSE . . . . . . . . . . . . . . . . . . . . 4 Stage of Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Time and Type of Herbicide Treatment . . . . . . . 4 Type of Herbicides Used . . . . . . . . . . . . . . . . . . . . 5 Foliar Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Root Penetration . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Translocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 RESEARCH NEEDS . . . . . . . . . . . . . . . . . . . . . . . . . . 10 LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . ll AUTHORS R. W. Bovey, agronomist, Science and Education Ad- ministration-Agricultural Research (SEA-AR), U. S. Department of Agriculture; The Texas Agricultural Experiment Station (Department of Range Science), College Station, Texas R. E. Meyer, plant physiologist, Science and Education Administration-Agricultural Research, U. S. Depart- ment of Agriculture; The Texas Agricultural Experi- ment Station (Department of Range Science), College Station, Texas AThe Response of Honey Mesquite t0 Herbicides SUMMARY Any environmental factors restricting the growth and develop- ment of honey mesquite at or near the proper time of herbicide application may reduce control. For example, translocation of sufficient herbicide may be restricted during periods of drought, cool weather, or cool soils (clay sites), or by damage to the foliage by insects, hail, or grazing. Application of herbicide too early in the life cycle will decidedly reduce herbicide transport to the lower stem and roots, since the translocating system may not be fully developed. Late applications (after Iuly 1), may present certain barriers to herbicide uptake by heavy cuticle develop- ment and/or restrictions to translocation because of inactive phloem. The type of herbicide and formulation also has a pro- found effect on herbicidal control. Many of the factors responsible for the effectiveness of 2,4,5-T in killing honey mesquite as outlined by research work prior to 1960 are still valid today, even though new herbicides are available and improvements in application techniques have been made. Recent research explains why honey mesquite control is affected by such factors as stage of growth, herbicide type, timing of application, certain leaf characteristics, moisture stress, and other environmental factors. Further research is needed to find more effective herbicides and better application techniques, and to elucidate conditions needed for obtaining optimal honey mesquite control. INTRODUCTION Mesquite (Prosopis spp.) occupies an estimated 93 million acres of range and pasture land in the Southwest (58). Fisher (30) indicates the species of major concern in the United States are velvet mesquite (Prosopis velutina) in Arizona, and honey mesquite (P. glandulosa) in California, Arizona, New Mexico, Utah, and Texas. Ac- cording to a survey made in 1964 (70), over half, 56 million acres, mostly of honey mesquite, grows in Texas. Native inhabitants and early settlers in the Southwest considered mesquite a source of fuel, building material, utensils, and weapons (30). Various foods, beverages, and medicines were made from the fruit (legume) or seed, and glue“ and candy were made from the gum exudate. The lelgumes are eaten by livestock and wild animals, the wood is often used for fuel, and the trees shade animals and provide ornamental value for people. f5 Mesquite, however, has spread, and population den- \. sities have increased to an extent that interferes with ranching operations and livestock production. It has been postulated (30) that the large influx of grazing animals during the last 150 years was the most important single factor influencing the increased density of mes- quite. The primary causes include overgrazing by live- stock, reduction in rangeland fires, and reduced compe- tition from grasses. Periodic drought also contributes to mesquite invasion by reducing competitive vegetative cover. Mesquite competes with desirable forage by being an extravagant user of soil water (60). Well-established trees may produce roots 15 to 40 feet deep or lateral roots that extend as far as 50 feet from the base of the plant (33). Mesquite roots have been found as deep as 125 feet in a mine (60). The extensive root system of mesquite makes it well adapted for competing with other vegetation and for survival during drought. The pres- ence of mesquite in extensive and dense stands on grazing lands is considered one of the major agricultural problems in the Southwest. Mesquite not only reduces production and utilization of herbaceous forage but also makes handling and locating of livestock difficult. Mes- quite also produces thorns injurious to humans, live- stock, and pneumatic-tire vehicles. t‘ ‘Q; Mesquite is presently controlled 0n grazing lands by mechanical methods (dozing, chopping, grubbing, mow- ing, root plowing, chaining), herbicides, and prescribed burning. Herbicides are easier, faster, and usually less costly to apply than most mechanical methods. The search continues, however, for more effective, less ex- t pensive herbicides that are safe to apply near cropland, gardens, and ornamental vegetation. Controlled fire and biological methods are being investigated, but her- bicides are likely to remain the most effective method for mesquite control. This paper explores the factors in- volved in herbicide effectiveness in controlling mesquite and will define the need for understanding the interac- tion among physiological processes of the plant, environ- mental conditions, and herbicide-related factors such as timing of application, formulation, application rate, dis- tribution on foliage, and mode of action. HISTORICAL REVIEW The most successful and economical broadcast her- bicide treatment for mesquite is aerial application of a low volatile ester of 2,4,5-T [(2,4,5-trichlorophenoxy)- acetic acid] (23). The herbicide has been applied in a 1:3 diesel oil/water emulsion carrier at 4 gallons per acre 40 to 90 days after bud break of honey mesquite in the (40). Early Research As early as 1946, Fisher et al. (31) developed methods to kill honey mesquite by application of kerosene or diesel oil to the lower stem and bud zone of individual trees. Fisher et al. (31) defined the anatomy and mor- phology of honey mesquite and showed that the dormant buds on the underground stem of mesquite‘ must be destroyed in order to kill the plant. The addition of 2,4,5-T ester (1.25 percent) to the diesel oil increases mesquite mortality (36). Additional work of Young and Fisher (76) indicated that wetting the base of the mes- quite plant with 0.5 percent solution of 2,4,5-T ester in oil was an economical and effective control measure for a limited number of trees. An effective cut surface treat- ment consisted of painting either the concentrated 2,4-D [(2,4-dichlorophenoxy)acetic acid] amine formulation or a 1 percent solution of an ester of 2,4,5-T in diesel oil on the exposed stem (38). As early as 1948, Fisher and Young (36) reported that sodium arsenite, sodium chlo- rate, ammonium sulfamate, sulfamic acid, ammonium thiocyanate, 2,4-D, and 2,4,5-T were the only chemicals out of seveifal‘ hundred tested that were absorbed by the foliage and‘ translocated in sufficient amounts to kill dormant buds on the underground stem. However, the researchers indicated that ideal conditions of absorption and translocation of chemicals were seldom attained in the Southwest, since moist contact of the chemical with the leaf surface was required for long periods (8 hours). Increasing chemical concentration on leaf surfaces above lethal concentrations did not improve translocation. 2 spring (35). Herbicide rate is 0.5 to 1.0 pound per acre It was reported in 1949 that an ester of 2,4,5-T applied to the foliage of mesquite was a more effective treatment ‘\ than several formulations of 2,4-D or other chemicals 7 (77). During the same year, aerial applications were made to mesquite in different seasons (37). Most effec- tive control was obtained at the full leaf stage (spring) with ample soil moisture (90 percent canopy reduction and 25 percent mortality). By 1951, an estimated 0.5 million acres of honey mesquite were treated commer- cially with broadcast foliar sprays of the ester of 2,4,5-T in Texas (41). Factors Affecting Results In 1956, Fisher et al. (32) defined the factors responsi-fi ble for the effective control of mesquite with 2,4,5-T. They included the following: 1. Effective control depends upon translocation of a toxic amount of 2,4,5-T from foliage to the crown tissues. 2. Greatest translocation of 2,4,5-T occurs during a 50- to 90-day period after the first leaves emerge in the spring (most favorable time of treatment). 3. Maximum translocation of 2,4,5-T occurs when total sugar content in roots is accumulating at a rapid rate following the low level at the beginning of the full leaf stage. 4. Minimum translocation of 2,4,5-T occurs when total sugars in roots are decreasing rapidly and when reducing sugars are relatively abundant. 5. Most effective control of mesquite with 2,4,5-T occurs when soil moisture is adequate, a heavy foliage cover is present, and after rapid growth of new leaves and stems has ceased. 6. Effectiveness of aerial application of 2,4,5-T is reduced when either drought-restricted growth or when intermittent rainfall causes irregular foliage growth. 7. Greater effectiveness of 2,4,5-T occurs when ap- plied to mesquite growing on sandy loam and deep sandy soils compared with heavy clay soils and on small plants with stems less than 3 inches in diameter compared with larger trees. 8. Carriers, whether oils alone, oil-water emulsions or water alone, have no apparent influence on the effectiveness of 2,4,5-T applications when used at 4, 8, or 12 gallons per acre total volume. 9. A rate of 0.5 pound per acre of low volatile ester of 2,4,5-T in 1:3 oil-water emulsion effectively and economically controls mesquite. Increasing the amount of 2,4,5-T does not increase the percent- age of mesquite killed. ."/ F) 10. Droplet size of sprays, formulation of 2,4,5-T, and? weather factors do not appreciably affect the effec- tiveness of 2,4,5-T. However, these factors must be considered in ease and safe handling of the herbicide under field conditions. Although the principles as outlined were established 25 years ago, they are still valid today for honey mes- ‘quite control in Texas. \ 1 i sn '1.’ Fisher et al. (32) indicated that the low volatile ester and suspended acids of 2,4,5-T were more consistent in killing mesquite than either the high volatile esters or the amine formulations. Tschirley and Hull (73), Rey- nolds and Tschirley (61), and Valentine and Norris (74) also found that the esters of 2,4,5-T were consistently more effective on velvet mesquite and honey mesquite than amine formulations. Behrens (8) reported that droplet size, spray volume, and herbicide concentration had no direct influence other than minor effects on response ‘of mesquite or cotton to 2,4,5-T, but that droplet spacing was of major importance. An average droplet spacing of 3100 microns, equivalent to a deposition rate of 72 droplets per square inch, was considered the maximum spacing that would maintain a high level of herbicidal effectiveness. Soil Treatments Effective mesquite control has been obtained by spraying a narrow band of soil around the base of trees with a suspension of monuron [3-(p-chlorophenyl)-1,1- dimethylurea] in water or by application of pellet formu- lations of monuron (33). Workers in New Mexico (57) also reported effective control of mesquite with monu- ron. Monuron was more effective than fenuron (1,1- dimethyl-3-phenylurea) or diuron [3-(3,4-dichlor- ophenyl)-1,1-dimethylurea]. Although the practice has never been used extensively in Texas, it demonstrates the first use of substituted urea herbicides for mesquite control. Herbicides such as picloram (4-amino-3,5,6- trichloropicolinic acid), dicamba (3,6-dichloro-0-anisic acid), karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], bromacil (5- bromo-3-sec-butyl-6-methyluracil), tebuthiuron (N[5- 1 , 1-eimethylethyl)-1 , 3, 4-thiadiazol-2-yl]-N,N’-dimethyl- urea), and prometon [2,4-bis(isprogylamino)-6-methozy- s-triazine] (20, 51, 64, 69) when applied as soil treat- ments for honey mesquite control, have generally been ineffective at economical rates. Herbicide Mixtures In 1967, Robison (62) was first to report that equal- ratio combinations of 2,4,5-T and picloram caused higher mortality of honey mesquite than either 2,4,5-T or pic- loram alone at equivalent rates of application. Bovey et al. (12, in nursery and greenhouse studies conducted in 1964 to 1967, reported results similar to those of Robison (62) using 2,4,5-T and picloram. However, paraquat:pic- loram (1:1) combinations were antagonistic on honey Q mesquite, indicating that paraquat reduced translocation \~ of picloram in mesquite, huisache, and bean plants. a owever, uptake and transport of picloram in honey mesquite were increased in the presence of 2,4,5-T, and this may partially explain its increased herbicide effect (26). Scifres and Hoffman (66) indicated that dicamba con- trolled about the same percentage of honey mesquite as equivalent rates of 2,4,5-T in the Rolling Plains, Coastal Prairie, and South Texas Plains. Combinations of 2,4,5-T and dicamba controlled no more honey mesquite than either herbicide alone, but dicamba was effectively sub- stituted for 2,4,5-T in combinations with picloram. Three-way combinations were no more effective than dicambazpicloram or 2,4,5-T:picloram mixtures. In East Texas, Meyer and Bovey (50) found dicambazpicloram (1:1) mixtures to be more effective on honey mesquite than dicamba, picloram, and 2,4,5-T, or two-way combi- nations of dicamba, picloram, or 2,4,5-T. Beck etf al. (6, 7) indicated that 2,4,5-T:picloram (trimethylamine salts) mixtures were more effective than either the ester or amine of 2,4,5-T when applied to mesquite resprouts of different ages (6) and in control- ling freshly shredded mesquite (7) at all dates of applica- tion. These data confirm earlier work on the effec- tiveness of the 2,4,5-T:picloram mixture compared to 2,4,5-T alone for honey mesquite control (12, 26, 35, 49, 50, 62, 66). Influence of Soil Temperature In 1971, Dahl et al. (25) reported soil temperature at the 18-inch depth was the most important factor affect- ing control of honey mesquite with aerial sprays of 2,4,5- T, and that best results occurred if soil temperatures were over 80°F. Sosebee et al. (71) indicated that soil temperature (IS-inch depth) above 75°F, relatively low soil water content (0- to 6-inch depth), and tree height (less than 8 feet) were most influential in mesquite mortalities using triethylamine salt of 2,4,5-T:picloram (1:1 ratio). Influence of Other Variables Meyeret al. (52), however, found that soil moisture at a depth of 2 to 3 feet was the most important environ- mental variable of those measured, relative to mesquite control with 2,4,5-T, picloram, or picloram:2,4,5-T mix- ture. Plant characteristics most closely associated with control were widest translocating phloem thickness, most rapid rate of new xylem ring radial growth, and lowest predawn leaf moisture stress. In other studies (49), rate of new xylem ring radial growth and thickness of translocating phloem were the factors appearing most often in predictive equations for mesquite control with either 2,4,5-T or 2,4,5-T:picloram (1:1) mixtures. Wilson et al. (75) predicted that best beginning dates for application of 2,4,5-T in West Texas were generally May 15 to June 15, and ending dates were from July 1 to July 15. The prediction was based on carbohydrate concentrations found in mesquite roots and the fact that phenoxy herbicides‘ such as 2,4,5-T are translocated to the roots when carbohydrates are accumulating there. In 1974, Fisher et al. (34) reported that low volume applications of 2,4,5-T or 2,4,5-T:picloram combinations at 0.25 to 0.5 pounds per acre of total herbicide were possible by aircraft for honey mesquite control. Variation in carrier volume from 0.5 to 4.0 gallons per acre did not significantly alter plant mortality. New Herbicides More recently, Iacoby et al. (46, 47) in field studies and Bovey and Meyer (18) in greenhouse research have indicated that triclopyr [(3,5,6-trichloro-2-pyridinyl)= oxyacetic acid] and 3,6-dichloropicolinic acid applied as foliar sprays have given excellent control of honey mes- A quite. Studies are being continued to define the parame- ters affecting results. The remainder of this paper ex- plores details of the mode-of-action of herbicides and the influence of environmental factors on the physiology and effectiveness of foliar and soil-applied herbicides on honey mesquite. FACTORS AFFECTING HERBICIDE RESPONSE Stage of Growth Honey mesquite is treated with herbicides at various stages of growth and in various forms. The two most common forms are the large, single-stemmed tree and the many-stemmed brush or small tree (54). Probably the many-stemmed plant is the most common form and may result from above or below ground growthfrom crown stem buds after damage from fire, grazing ani- mals, mowing, drought, or herbicide injury. A third type of growth is the more or less decumbent or “running” type brush or shrub. Most stands of mesquite, are composed of distinct size and age classes. Such plants become established from seed during periods favorable to germination and estab- lishment, often followingsevere overgrazing" or other factors, such as drought, that reduce herbaceous vegeta- tive cover. 'The life cycle of mesquite is characterized by three distinct stages: seed germination and seedling establish- ment, juvenile plant, and mature plant (39). During herbicide spraying operations, one or more life stages may be present in the same pasture. Mesquite in differ- ent stages of growth can respond differently to the same herbicide treatment. Fisher et al. (32) indicated young plants with stems less than 3 inches in diameter were more effectively controlled with 2,4,5-T than older trees. Lack of vigor and poor foliage cover may be responsible for lower percentage mortality obtained on old trees. Fisher et al. (32) also indicated control of regrowth with 2,4,5-T originating from the crown buds (above-ground growth from damaged trees) was effective when new growth reached a height of 4 feet or more and attained heavy foliage. They indicated that there must be a balance of above-ground growth with that of the root system for most effective control. In other words, aerial growth (leaves) must be sufficient to intercept and translocate lethal quantities of herbicide to the crown zone. A single application of 2,4,5-T usually controls the plant population for 5 to 7 years before retreatment is necessary because of resprouting and recovery of the original plants. Plant mortality is typically 20 to 30 percent in northwest Texas with 2,4,5-T aerial sprays (35). a Control of creeping or running mesquite in Texas requires application of 2,4,5-T for 3 successive years 4 (40). Apparently, the vigorous growth and extensive root system requires repeated 2,4,5-T exposure for adequate v translocation to the roots. Velvet mesquite in Arizona requires two treatments for best control, which may be in consecutive years or 2 years between treatments, depending upon rate of regrowth following the initial application (72). Greenhouse-grown and nursery plants respond to her- bicides as does mesquite growing in natural stands (3, 9, 12, 15, 16, 17, 18, 26, 27, 28, 29, 53, 63, 67). Seedlings growing under field conditions are also susceptible to herbicides unless shootzroot ratios are such that aerial growth is inadequate to intercept and transport lethal amounts of herbicide to the crown zone. Large root biomass to aboveground biomass ratios occur if aerial (livestock, wildlife, or rodents), fire, or mechanical means. However, mesquite seedling mortality occurs if the stem is severed below the cotyledonary node (17, 54, 65). The younger the seedlings, the higher the mortality of mesquite from 2,4,5-T or picloram (17). For example, picloram or 2,4,5-T at 0.25 pound per acre killed 100 and 92 percent of 1-week-old plants and 37 and 17 percent of 16-week-old plants, respectively (17). . Beck et al. (6) studied the effect of 2,4,5-T amine, 2,4,5-T ester, and the trimethylamine salts of 2,4,5-T plus picloram (1:1) on honey mesquite resprouts 1, 7, and 14 years old under field conditions. No consistent differences were obtained between age of regrowth and level of control; however, the 2,4,5-T:picloram mixture was most effective at all dates of application (May, June, Iuly or August). Beck et al. (6) suggested that equally effective control at some dates of application on 1-year- old resprouts and possibly some of the 7-year-old re- sprouts was due to absorption and translocation of her- bicide by the green, succulent stems of the new growth and the close proximity of application to the crown zone. Beck et al . (7) also reported excellent control of honey mesquite by simultaneous shredding and spraying. The 2,4,5-T:picloram mixture (trimethylamine salts) was con- sistently more effective than the amine or ester of 2,4,5- T. May treatments were more effective than those ap- plied in June, July, August, or October 1972. Herbicide rate was not given. Time and Types of Herbicide Treatment The pioneering work of Fisher et al. (32) established that mesquite was most susceptible to 2,4,5-T sprays 50 to 9O days after bud break which usually occurs from May 15 to the first week in July. This period corresponds to cessation of leaf and twig growth (full leaf develop- ment) and the beginning of radial stem, trunk and root growth in the tree (39). Other researchers using foliar sprays of 2,4,5-T, picloram, and dicamba or various mixtures of these herbicides have confirmed F isher’s findings (6, 7, 12, 25, 40, 49, 50, 61, 62, 66, 71, 72, 73, 74). Application of herbicides to the foliage at othe times during the year is usually not very effective unless N it is a drenching spray made during the summer months to individual plants. '1) growth has repeatedly been removed either by grazing. ~.\ \ I have been investigated include diuron, fenuron, monu- ron, sodium arsenate, sodium chlorate, tebuthiuron, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1 methyl- 1,3,5-triazine-2,4(1H,3H-dione] (10, 20, 33, 51, 57, 64, The cut-stump method involves treating the freshly- cut stump surface with herbicide (64). Hoffman (40) ‘fiuggested using 8 pounds of 2,4,5-T in 100 gallons of diesel oil or kerosene and applying the mixture to the cut m (I 20, 51, 64). Q One of the most effective soil-applied herbicides, .\\ surface until the solution runs down the bark to the root crown. Using the cut-stump method, the herbicide may be poured on the stump or applied with various types of hand or power sprayers. Although the cut-stump meth- od is effective, considerable time and expense may be saved by using the basal treatment method (64). The basal treatment consists of spraying or wetting the trunk with adequate liquid or spray to cause runoff from a height of 12 inches to the ground line, with enough solution to soak into the crown zone (40). Mesquite with Aa trunk diameter of 5 inches or less can be treated with asal herbicide sprays as used with the cut-stump meth- od. Kerosene or diesel oil is also effective when the crown zone is throughly soaked. Trees with trunks great- er than 5 inches in diameter should be frilled with an axe or similar tool and herbicide applied into the cuts. Cut-surface, trunk-base, or frill treatments can be applied any season of the year, but best results are from summer or winter applications (40). Applications to cut- surfaces and trunk bases are more effective during dry periods when the soil is not fused to the tree trunk and liquid can penetrate to the root crown. Better control is obtained on sandy, rocky, or porous soils than on clay soils. Soil-applied herbicides can be applied any time of the year but are most efficient in killing mesquite when applied prior to a sufficient amount of rainfall to leach the herbicide into the root zone. Mesquite, however, is difficult to kill with soil-active herbicides, especially when growing in clay soils. Types of Herbicides Used Types of herbicides applied, methods of application, and the response of honey mesquite to the treatments are shown in Table 1. In actual field use, foliar sprays include 2,4,5-T, 2,4,5-T:picloram, or 2,4,5-T:dicamba in 1:1 combinations usually applied at a total rate of 0.5 to 1.0 pound per acre of herbicide. More recently, tri- clopyr and 3,6-dichloropicolinic acid are showing pro- mise as foliar sprays for honey mesquite control (16, 18, 46, 47). All these herbicides are hormone-like, growth reg- ulator compounds, which are absorbed through leaf and stem tissue and are translocated to other plant parts from 71116 point of application. Picloram, dicamba, triclopyr, and 3,6-dichloropicolinic acid are also effective her- bicides via root absorption on many species and honey mesquite in the greenhouse (3, 9, 15, 16, 20, 64). However, under actual field conditions, the control of honey mesquite via root uptake from picloram and di- camba applied tolthe soil has not been effective (9, 10, specially in sandy soils, for control of honey mesquite is s arbutilate (Table 1). Unfortunately, the compound is no longer commercially available for use on rangeland in the United States. Other soil-applied herbicides that 69, 74). Basal sprays and the injection/cut surface treatments are discussed above. Chemicals used for both methods are listed in Table 1. Basal sprays or pours with kerosene, diesel oil, or diesel oil plus 2,4,5-T ester are a common practice to kill scattered trees of honey mes- quite. F oliar Absorption Foliar-applied herbicides must» be absorbed by leaf and stern tissue and translocated to the crown zone of honey mesquite to kill the plant. Factors affecting foliar absorption are examined in the discussion that follows. Herbicide Type Herbicides vary in rate of foliar penetration. Davis et al. (27) studied the uptake of picloram and 2,4,5-T in leaves of 10 woody species including honey mesquite and found that in most species picloram entered faster and accumulated at higher concentrations than 2,4,5-_T. In other studies (28), honey mesquite leaves alsowab- sorbed picloram more rapidly and extensively than 2,4,5-T, but moisture stress reduced foliar uptake of picloram, whereas absorption of 2,4,5-T was unaffected. More recently, Bovey and Mayuex (16) found higher concentrations of 3,6-dichloropicolinic acid than 2,4,5-T, triclopyr or picloram in honey mesquite stems and roots 3, 10, and 30 days after application to soil or foliage in the greenhouse. Herbicide Formulation Morton et al. (56) found larger amounts of 2,4,5-T in honey mesquite leaves treated with the butoxyethyl esters of 2,4,5-T than with the ammonium salts. Concen- tration of 2,4,5-T translocated to the stems, however, was similar. Most data suggest that ester formulations of the phenoxy herbicides penetrate leaf surfaces more readily than amine salts (43). This may or may not result in greater accumulation of herbicide in the roots, since the esters are not translocated as readily as the amine salt formulations (22, 42). Carriers and Adjuvants Fisher et al . (32) evaluated a wide range of oils and oil- water emulsions as well as water as 2,4,5-T spray carriers for control of honey mesquite. The 1:3 diesel fuel oil- water emulsion was considered equally effective and more economical to use than specially formulated oils. In some instances, use of water alone as the carrier reduced the effectiveness of the 2,4,5-T application. Hull (42) indicated similar results on velvet mesquite. A nontoxic oil in a 1:4 oil-water emulsion as a carrier for 2,4,5-T resulted in considerably greater injury to the nontreated distal foliage than diesel oil as a carrier. Behrens (8) found that when diesel fuel alone was used as the carrier on greenhouse-grown plants at spray volumes of 12.5 and 32 gallons per acre, effectiveness was reduced com- pared to 4 gallons per acre. The reduced effectiveness 5 Spray Characteristics Spray droplet size affects phytotoxicity depending up- \ K 0n species studies. In some species, herbicidal efficiency“ * was attributed t0 the phytotoxicity of the diesel fuel, which caused rapid killing of the leaves, limiting 2,4,5-T translocation. More recently, Scifres et al. (63) found 7"‘ “s; that absorption of 2,4,5-T ester was more rapid in a paraffin oil carrier than in diesel fuel, water, or emul- sions of the oils in water carriers. No significant differ- ences in percentage mesquite control have resulted from foam carriers (68), compared with conventional sprays or addition of sufactants to the spray solution (19). Most commercial herbicide formulations have sufficient sur- factant and wetting properties for wetting plant surfaces, and the addition of most surfactants or emulsifiers to the spray solution may have limited effect. Spray carrier volume may influence herbicide results. Carrier volumes equivalent to 4, 20, and 100 gallons per acre [oil-water (1:3v/v)] with 0.5 pound per acre of the 2- ethylhexyl ester of 2,4,5-T were applied to nursery- grown honey mesquite (19). Herbicide applied at 20 gallons per acre using hand-carried sprayers reduced the canopy more than when applied at 4 or 100 gallons per acre. Compared to 20 gallons per acre, 4 gallons per acre may have resulted in insufficient coverage of the foliage whereas 100 gallons per acre may have resulted in loss of the herbicide from plant surfaces in excessive runoff. Variation in carrier volume from 0.5 to 4.0 gallons per acre containing 0.25 to 0.5 pound of 2,4,5-T per acre of 1:1 combination of 2,4,5-T and picloram when applied by aircraft did not significantly affect honey mesquite mortality (34). Meyer et al. found that mesquite leaves were func- tional in herbicide uptake for about 4 days after applica- tion. However, maximum absorption apparently oc- curred the day of spraying. Thus, any agent or force which causes leaf removal too , quickly after spraying reduces control. In most cases, it is important to use a carrier which will penetrate the waxy surface of the leaf but will not kill the leaves or cause abscission soon after spraying Acidity Uptake of 2,4,5-T-1-14C by immersion of honey mes- quite leaflets into solutions rapidly diminished as pH was increased from 3.5 to 5 in the treating solution Leaves treated with droplets at pH 3.5 and kept moist absorbed about 92 percent of available 2,4,5-T-1-14C during the first 3 hours of exposure, with no additional uptake between 3 and 5 hours. Comparable leaflets treated with droplets that were allowed to evaporate absorbed only 30 percent of available 2,4,5-T-114C dur- ing the first 3 hours and an additional 10 percent be- tween 3 and 5 hours. Leaflets continued to absorb 2,4,5- T-l-MC for about 14 to 24 hours after treatment with pH 3.5 droplets that were allowed to evaporate, but those kept moist-l did not absorb 2,4,5-T-1-14C after 3 hours, presumably because of lack of available 2,4,5-T-1-14C. decreases as droplet size increases above 500 microme- ’ ters in diameter (43). An average droplet deposition of 72 droplets per square inch is considered the maximum spacing that maintains a high level of herbicidal effec- tiveness when 2,4,5-T is applied to honey mesquite and cotton Droplet size, spray volume, and herbicide concentration have no direct influence Air Temperature and Relative Humidity Morton (55) treated honey mesquite seedling leaves with 5 p.g of carboxyl-labeled 2,4,5-T and found more 2,4,5-T absorbed at 100°F than at 70° or 85°F after 72 hours. Approximately 50 percent of the 2,4,5-T applie to a single leaf was absorbed. Only slight differences in absorption were found at different humidity levels. Rainfall Bovey and Diaz-Colon (13) found that oil-soluble for- mulations (esters) of 2,4,-D and 2,4,5-T, and picloram were less affected by artificial rainfall than water-soluble herbicides such as paraquat (1, 1’dimethyl-4,4’- bipyridinium ion) and cacodylic acid (hydroxydimethyl- arsine oxide) on guava (Psidium guajava L.) and mango (Mangifera indica L.). The oil-soluble phenoxy her- bicides usually retained their effectiveness even when leaves were washed within 15 minutes after treatment. Field-grown honey mesquite leaves showed complete leaf necrosis even when leaves were washed 20 minutes after treatment with paraquat, indicating rapid absorp- tion (11). Winged elm (Ulmus alata Michx.) and live oak (Quercus virginiana Mill.) showed little injury under the same conditions. Moisture Stress Merkle and Davis (48) showed that foliar absorption of 2,4,5-T and picloram in beans (Phaseolus vulgaris L. var. Black Valentine) was unaffected by extreme moisture stress. Moisture stress reduced foliar uptake of picloram in honey mesquite but not in winged elm (28). Moisture stress did not affect absorption of 2,4,5-T in honey mesquite. Light Light assists herbicidal penetration by stimulating stomatal opening in most species (1). Measurement of herbicide absorption byhoney mesquite as influenced by quality and intensity of light has not been deter- mined. Brady (24), however, found that the absorption of the isooctyl ester of 2,4,5-T increased as light intensity increased up to 2,680 foot candles, but it decreased thereafter in post oak (Quercus stellata Wangenh) and water oak (Quercus Nigra L.). Absorption of 2,4,5-T increased as light intensity increased up to 6,000 foot candles in long leaf pine (Pinus palustris Mill.) and _ Under laboratory conditions, weak acids penetrate best American holly (Ilex opaca Ait). Davis et al. (27) found“ at low pH values where the molecules are largely in the undissociated form (22). In this state, they more readily penetrate the lipoidal phases of the cuticle and leaf cells. However, under field conditions, little benefit of im- proved control has been shown by adjusting pH of the spray solution. 6 that uptake of picloram by live oak leaves decreased a \ light intensity increased. Scifres et al. (67) found that honey mesquite seedlings" which developed under shade (low-light intensity) were more easily killed by 2,4,5-T sprays than seedlings grown in sunlight. The increased effectiveness under rooting solution over a 5-day period, whereas huisache, a shade may have been due to limited cuticle develop- more susceptible plant, showed no redistribution or loss ament (45) and, hence, greater herbicide uptake. Baur of picloram. and Swanson (5) found that honey mesquite grown dur- ing short days was more susceptible to 2,4,5-T or pic- Translocation lotatn than that gtewn dining hing daYs- The teasen fer a Once an herbicide is absorbed by leaves and stems, a this difference is not clear but may be related to cuticular key faetoi in killing mesquite is ttansleeatieii ef the tleveloprnent- phytocide to the base of the stem. The phloem is the Leaf Structure and Develepment principal food-conducting tissue in vascular plants. Com- As indicated earlier, the best time for application of ponntlS ltlte 2>4>5‘T are tranSloeatetl through the phloem foliar herbicides for honey mesquite control is during a trorn r eglonS or earhohytlr ate SyntheSlS (leaVeSl to Sugar" 50- to 90-day period after the first leaves emerge in the lrnportlng tlSSheS Sheh aS rootS> hhtlS> Shoot tlpS’ SeetlS spring By May 2Q, leailets of honey mesquite in Brazos and fruit, and other leaves. The direction of herbicide County have usually attained full maturity (54). The rnovernent 1S tleterrnlnea _hy_ the patterns or tootl tllS' a,upper outiole is usually 5 to 8 rniorons thiok and the tribution and utilization within the plant, since translo- ‘ a lower cuticle is usually 2 microns thick; however, pene- eatlon ot tootl may alSo oeehr trorn rootS to leaVeS or tration of the cuticle by herbicides appears sufficient for between other plantpartS <22)‘ ltleally> _at leaSt tor the herbicidal effect and translocation to other parts of the phenoxy herhleltleS> lt 1S heSt to apply rollar SprayS when plant ln rnost plants there is a relationship hetween food transport is occurring from the leaves (basipetal) to outioular development and oornposition, and foliar ah_ other plant parts (roots) so as much herbicide as possible sorption of herbicides (45). The more mature the leaf, 1S tranSloeatetl to the haSe or the Sterrr _lh the eaSe ot the greater the cuticular development, and that may noneY inesqiilte, ihlS Occurs under springtime condi- partially explain the resistance of honey mesquite to tlonS attertollage lS rnathr e enotlgh to export Sugar? and herhioitle sprays applied late in the growing season, the plant is rapidly growing radially. If the herbicide is even though limited stomatal penetration can occur applled at other tlrneS tltlrlng the year’ reSttltS may he when outioules heoorne Very thiok (45% unsatisfactory since assimilate (food) movement may be limited. For successful chemical control of honey mes- Metabolism and Degradation quite, movement of phytotoxic materials to regenerative Marten (55) tennd that aPPieXitnatelY 8o Pereent 0t tissues (buds) is necessary to eliminate their growth the 2=4>5'T ahsethed h)’ leaves et heneY inesqnite seed" potential. The greatest concentration of buds occurs on lings was metabolized after 24 hours. Metabolism was the trunk in the first fOOt bglgw Soil line (31, 32, 35, 54, eeinPleteiY inhibited at 50°F, and a lewef ‘Tate 0f Fisher and Young(36) reportedin 1948 that sodium inetahehstn Was neted at 100° than at 70° and 85°F arsenite, sodium arsenate, sodium chlorate, ammonium Picloram, however, is more resistant to degradation in Sulfomate, Sulfuric acid, ammeniiim thiticyanate, 2,41), Plants than 2>4»5'T (21) and 2,4,5-T were the only chemicals out of several hundred tested that were absorbed by the foliage and 300i Pelletfatiml translocated in sufficient amounts to kill dormant buds Field Studies on the underground stem. Increasing chemical concen- tration of leaf surfaces above minimum lethal concentra- tions did not improve translocation. In 1949, Young and Fisher (77) reported that the ester of 2,4,5-T was a more effective treatment than several formulations of 2,4-D or other chemicals. Early in the 1960’s, picloram was discovered to be an effective herbicide for controlling honey mesquite and other woody species The picloram:2,4,5-T combina- tion (12, 62) was particularly useful. Davis et al. (26) in 1968 found that transport of picloram to the lower stem in honey mesquite was increased in the presence of 2,4,5-T whereas the uptake and transport of 2,4,5-T was decreased in the presence of picloram. Increasing ratios As indicated earlier, control of honey mesquite by soil-applied herbicides has not been highly effective in the field. However, triclopyr, picloram, and 3,6- dichloropicolinic acid are highly effective when applied to soil in pots supporting honey mesquite under greenhouse conditions. Possibly the extensive root sys- tem of honey mesquite and impermeable heavy clay soils in some areas may partially preclude effective control under field conditions. However, honey mesquite was more effectively controlled in the field when liquid formulations of karbutilate and tebuthiuron were applied subsurface, than on the soil surface (51). Laheratery Studies of 2,4,5-T:picloram in mixtures up to 16:1 continued to Baur and Bovey (3) studied changes in the concentra- increase uptake and transport of picloram; the reverse tion of piclorarnfin roots, stems, and leaves of 20-day-old effect occurred for 2,4,5-T when 2,4,5-T:picloram ratios huisache and honey mesquite plants exposed for differ- were decreased. More total herbicide was transported ent lengths of time. Exposing roots to aqueous solutions when the 2,4,5-T:picloram combination was used than of picloram for 24 hours killed about 6O percent of the either herbicide used alone at equal rates. This may help “treated plants. It took 1O times more herbicide to give to explain the greater effectiveness of ‘the herbicide S“ the same response in honey mesquite (10 ppm) as combination in controlling honey mesquite. When para- huisache (1 ppm). .In honey mesquite, picloram was quat was combined with picloram on honey mesquite, redistributed and eventually lost from the plant into the huisache, and bean, transport of picloram to the lower 7 stem was reduced because of damage of the transport Temperature and Relative Humidity sYstem h)’ Paraquat- Translocation of 2,4,5-T in honey mesquite seedlings III StUdiGS, Davis 8t al. fOUIId that high€St was primarily basjpetal (dgwnward) ffom the pgint Q concentrations of 2,4,5-T, picloram, or combinations of application at 70°F, hoth acropetal (upward) and hasipet- 2,4,5-T:picloram in phloem were associated with dates of al at 85°F, and only a short distance acropetal at 1()()°F best control of honey mesquite established by numerous (55)_ The quantities of 5354,5111 translocated into nn- investigatiens- Adding 2>4>5'T te Pieter am eaused an treated tissues at 100°F were less than at 70° and 85°F. increase in the amounts of picloram in the phloem in The highest concentrations of 2,415-1‘ were found in teur at five dates at aPPheatien (29) These data agree tissues with highest soluble sugar concentrations. From with the laboratory and greenhouse investigations de- 3 to 27 percent of the 2,4,5-T ahsorhed by honey ines_ serihed aheVe (26) Therefore, the eemhinatien at Pie’ quite leaves was subsequently detected in untreated loram and 2,4,5-T is generally more effective than either stern, leaf, and root tissues Total arnonnts of C14 (car- herhieide aPPtied atene- boxyl-labeled 2,4,5-T) detected in the untreated tissues More recently, Bovey and Mayuex (16) studied the of the seedlings tended to increase, particularly in the €ff6CtiV6I16SS and tIHIISPOIt 0f 2,4,5-T, PiClOTHIII, tri- roots and lower stems, with increasing humidity. < ,_ clopyr, and 3,6-dichloropicolinic acid in honey mes- Radesevieh and Bayer (59) fQund that 2,4,5-T, tri- quite. Higher concentrations of 3,6-dichloropicolinic clopyr, and picloram transport was greater in periods of acid than 2,4,5-T, triclopyr, or picloram usually were warm temperatures (84° and 55°F day and night) and fOImd in honey mesquite Stems and r008 3, 10, and 30 long days (16-hour photoperiod) than cool temperatures days after application to soil, foliage, or both. This may (55° and 35°F day and night) and a 12-hour photoperiod be one reason why 3,6-dichloropicolinic acid is highly in five plant speejes as revealed by autgradiggraphg, effective in controlling honey mesquite. They found little metabolism of any herbicide, and each herbicide moved readily in the symplast (phloem); how- Herhieide Fermutatien _ ever, root application revealed limited apoplastic (xylem Although Morton et al. (56) found larger amounts of stream) mobility. 2,4,5-T in honey mesquite leaves treated with butoxy- Light ethyl ester than the ammonium salt, concentrations of 2,4,5-T in the stem were equal. Hull (42) reported in velvet mesquite that when carried in a nontoxic oil emulsion, the free acid, and the triethylamine and sodium salts of 2,4,5-T all demonstrated a greater ten- dency to be translocated to more distant portions of the plant than did ester formulations, even though contact injury to the treated leaves was less. Tschirley and Hull (73) however, found the ester of 2,4,5-T consistently more effective than the amine formulation on velvet Light intensity affected translocation of 2,4,5-T to the roots of woody plants (24). There was a negative linear relationship between light intensity and 2,4,5-T content of post oak roots. In water oak roots, however, herbicide levels increased as light intensity increased. In longleaf pine and American holly, translocation was not signifi- cantly influenced by light intensity. Herbicide transloca- tion in honey mesquite as influenced by light has not been measured. mesquite under field conditions. Research data of Fisher Moisture Stress at al- (32) en hene)’ mesquite agree With that at ethers Moderate moisture stress in beans did not have a (73) in that the 10W Vetatite esters and suspended aeids significant effect on the translocation of picloram but did were more consistent in killing mesquite than either the have on the translocation of 2,4531‘ (43). Advanced high Vetatiie esters er the amine termulatierls- The stress significantly reduced the translocation of both reasens fer the suPerier Pertermanee 0t the ester at herbicides. However, translocation of 2,4,5-T was appar- 24,531“ ever the amine termutatien has net been eteartY ently more sensitive to changes in moisture stress than estahhshed> hut the ester termulatien Prehaht)’ Pene" was translocation of picloram. Picloram was more mobile trates the WaX and eutiele en the teat mere r eaditY than than 2,4,5-T at all moisture stress levels studied. After 4 the amine- HeWeVen Beek et al- (d 7) sheWed little hours, as much picloram was translocated to the apex difference in effectiveness between the ester and amine and central stern of hean plants from a 24 microgram formulations of 2,4,5-T on honey mesquite. Differences application as there was 2,415-1‘ at 3 honrs after a 5() in termutatien ma)’ have been masked h)’ high rate 0t microgram application. This agrees with studies on hon- aPPtieatien er h)’ the taet that sPraYs Were aPPtied te the ey mesquite in which both herbicides were detected in hase 0t the Ptants- the apex only 4 hours after treatment, but only picloram occurred in the roots (28). After 24 hours, the apex and Carriers and Adjuvants roots contained more picloram than 2,4,5-T. The Scifres et al. (63) compared water, diesel oil, water: phloem-cortex accumulated greater quantities of pic- diesel oil (1:4) emulsion, paraffin oil, and waterzparaffin loram than the xylem-pith, indicating major transport via oil (1:4) emulsion for carriers of 0.5 pound per acre of the the symplast. After 9O hours, herbicide concentrations in butyl ether esters of 2,4,5-T. No differences related to most tissues were unchanged or higher than after 24 carrier occurred in the amount of 2,4,5-T translocated to hours. These data support observations by Meyer et al. the stem and roots, although greater amounts of her- (53) which indicated a period of 3 to 4 days was required bicides were absorbed by leaves treated with diesel or for honey mesquite to absorb and translocate herbicide paraffin oil carriers. for maximum killing of stems. Moisture stress sufficient 8 TABLE l. GENERAL RESPONSE OF HONEY MESQUITE TO VARIOUS HERBlClDESl P“ Application methodz ‘l,<:l'blClCl€ Chemical name BS FS I/CS ST AMS Ammonium sulfamate S3 Bromacil 5-bromo-3-sec-butyl-6-methyluracil R R Cacodylic acid Hydroxydimethylarsine oxide S-I Dicamba 3,6-dichloro-o-anisic acid S S R 2,4-D (2,4-dichlorophenoxy)acetic acid S-I S-I 3,6-DPA 3,6-dichloropicolinic acid S Dichlorprop 2-(2,4-dichlorophenoxy)propionic acid I Diesel oil ' S Diuron 3-(3,4-dicholorophenyl)-1-1-dimethylurea I-R DSMA disodium methanearsonate ' S FP- uron 1,1-dimethyl-3-phenylurea I-R L‘ , hosate N-(phosphonomethyl)glycine I-R Hexazinone 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine- I-R 2,4(1H,3I-l)-dione Karbutilate tert-butylcarbamic acid ester with 3(m-hydroxypheny|)-1, S-I 1-dimethylurea Monuron 3-(p-chlorophenyl)-1,1-dimethylurea I-R Paraquat 1,1’-dimethyl-4,4’-biphyridinium ion I-R Picloram 4-amino-3,5,6-trichloropicolinic acid S R Prometon 2,4-bis(isopropylamino)-6-methoxy-s-triazine I-R Silvex 2-(2,4,5-trichlorophenoxy)propionic acid S Sodium arsenite S Sodium chlorate I-R 2,3,6-TBA 2,3,6-trichlorobenzoic acid R Tebuthiuron N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazo|-2-y|]-N,N’- I-R dimethylurea 2,4,5-T (2,4,5-trichlorophenoxy)acetic acid S S S-I Triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid S 2,4-D + 2,4,5-T S-I 2,4-D + picloram S-I 2,4,5-T + dicamba S 2,4,5-T + picloram S Picloram + dicamba S lReferencesz 6, 7, 9, 10, 12, 16, 18, 19, 20, 21, 31, 33, 35, 36, 37, 38, 40, 46, 47, 49, 50, 51, 52, 57, 62, 64, 66, 69, 71, 74, 76, 77. 2B5, FS, I/CS and ST = basal spray, foliar spray, injection (cut surface treatment, and soil treatment, respectively.) 3S, S-I, l, l-R, and R = susceptible, susceptible to intermediate, intermediate, intermediate to resistant, and resistant, respectively, to honey mesquite. to slow growth markedly reduced transport of picloram and 2,4,5-T into untreated tissues. Bovey et al. (14) found that 1:1 combination of the triethylamine salts of translocating phloem thickness, most rapid rate of new xylem ring radial growth, and lowest predawn leaf mois- ture stress. Environmental variables most clearly as- picloram:2,4,5-T was more effective on huisache and Macartney rose when applied in the evening than in the morning or at midday in field studies. Internal water stress of the plants was less at night after the 6:00 p.m. treatment than after the 6:00 a.m. or 1:30 p.m. treat- ment, allowing more favorable environment for absorp- tion and translocation of the herbicide. Other Factors Meyer et all. (52) sprayed honey mesquite in the field sociated with honey mesquite control were lower max- imum air temperatures of 77° to 96°F 1 week before treatment, maximum soil temperature of 63° to 79°F at a depth of 3 feet 1 week before treatment, and decreasing percent soil moisture from 25 to 18 percent at a depth of 2-3 feet 1 week before treatment. In subsequent studies (49) of responses to spraying on 36 dates from March to October during a 4-year period, percent honey mesquite canopy reduction was directly correlated with total (‘with three herbicides at 14 different dates during 1969 6nd 1970. Most effective control of honey mesquite phloem thickness, rate of new xylem ring radial growth, and rate of upward methylene dye movement in the xylem and was inversely correlated with minimum leaf moisture stress. Rate of new xylem ring radial growth and thickness of translocating phloem appeared most often in the equations. A ccurred from treatments applied between April 30 and j ]uly 6. Picloram and a picloram:2,4,5-T (1:1) mixture ' were the most effective herbicides. Plant characteristics most closely associated with control included widest Dahl (25) indicated soil temperature at the 18-inch depth was the most important factor affecting response of honey mesquite to 2,4,5-T application in the spring. Temperatures at this depth in the high 60°’sF or low 70°’sF resulted in no mesquite mortality; best results occurred when temperatures were over 80°F. Proper phenological development of mesquite and soil moisture were important factors in combination with other vari- ables. Mesquite trees on upland and sandy sites were easier to kill with 2,4,5-T than those growing on bottom- land and clay sites because the soil is usually several degrees F warmer on upland and sandy sites. Nitrogen fertilizer did not enhance the control of honey mesquite when sprayed with 2,4,5-T after fertiliz- er application (2). Ammonium nitrate fertilizer has no effect on the nitrogen or the niacin levels in honey mesquite. RESEARCH NEEDS The following areas need serious investigation if we are to improve present mesquite control measures with herbicides and increase our understanding of the physi- ology, biochemistry, and mode-of-action of herbicides and growth regulators; 1. in-depth understanding of assimilate and water move- ment in honey mesquite under well-defined conditions 2. better understanding of the mode-of-action, metabol- ism, absorption, and translocation of herbicides pre- sently used for honey mesquite control 3. investigation of methods to modify the susceptibility of honey mesquite to herbicides by use of growth regulators, surfactants, herbicide combinations, anti- transpirants, and other adjuvants 4. determination of the most important environmental factors affecting the susceptibility of honey mesquite to herbicides 5. search for more effective and efficient chemicals for honey mesquite control 6. research on integrated honey mesquite management systems where two or more control methods are applied in a well-planned sequence. 1O J a 10. 11. 12. 13. 14. 15. 16. 18. 19. LITERATURE CITED .'Anonymous. 1968. Physiological aspects of herbicidal action. P i 146-163, Chap. 9. In Principles of Plant and Animal Pest Control. Vol. 2. Weed Control. Nat. Acad. Sci. Publ. 1597; Washington, D. C. . Arnold, J. D. and D. F. Burzlaff. 1978. The influence of am- monium nitrate on the control of mesquite resprouts with 2,4,5-T ester. J. Range Manage. 31:312-313. . Baur, J. R. and R. W. Bovey. 1969. Distribution of root-absorbed picloram. Weed Sci. 17:524-528. . Baur, J. R., R. W. Bovey, and I. Riley. 1974. Effect ofpH on foliar uptake of 2,4,5-T-1-14C. Weed Sci. 22:481-486. . Baur, J. R. and C. R. Swanson. 1968. Effect of nutrient level and daylength on growth and susceptibility of mesquite and huisache to 2,4,5-T and picloram. P 35-38. In Brush Research in Texas. Tex. Agric. Exp. Stn. Consol. PR-2583-2609, Texas A&M Univ., Col- lege Station, TX. . Beck, D. L., R. E. Sosebee, and E. B. Herndon. 1975. Chemical control of mesquite regrowth of different ages. J. Range Manage. 28:408-410. . Beck, D. L., R. E. Sosebee, and E. B. Herndon. 1975. Control of honey mesquite by shredding and spraying. J. Range Manage. 28:487-490. . Behrens, R. 1957. Influence of various components on the effec- tiveness of 2,4,5-T sprays. Weeds 5:183-197. . Bovey, R. W. 1971. Hormone-like herbicides in weed control. Econ. Bot. 25:385-400. Bovey, R. W. 1977. Response of selected woody plants in the United States to herbicides. USDA, ARS Agric. Handb. No. 493. 104 p. Bovey, R. W. and F. S. Davis. 1967. Factors affecting the phy- totoxicity of paraquat. Weed Res. 7:281-289. Bovey, R. W., F. S. Davis, and H. L. Morton. 1968. Herbicide combinations for woody plant control. Weeds 16:332-335. Bovey, R. W. and J. D. Diaz-Colon. 1969. Effect of simulated rainfall on herbicide performance. Weed Sci. 17:154-157. Bovey, R. W., R. H. Haas, and R. E. Meyer. 1977. Daily and seasonal response of huisache and Macartney rose to herbicides. Weed Sci. 20:577-580. Bovey, R. W., M. L. Ketchersid, and M. G. Merkle. 1979. Distribution of triclopyr and picloram in huisache (Acacia far- nesiana). Weed Sci. 27:527-531. Bovey, R. W. and H. S. Mayuex, Jr. 1980. Effectiveness and distribution of 2,4,5-T, triclopyr, picloram, and 3,6- dichloropicolinic acid in honey mesquite (Prosopis juliflora var. glandul0sa).Weed Sci. 28:666-670. . Bovey, R. W.and R. E. Meyer. 1974. Mortality of honey mesquite and huisache seedlings from herbicides and top removal. Weed Sci. 22:276-279. Bovey, R. W. and R. E. Meyer. 1980. Potential herbicides for brush control. J. Range Manage. 34:144-148. Bovey, R.JW., H. E. Meyer, and H. L. Morton. 1979. Use ofa woody plant nursery in herbicide research. Tex. Agric. Exp. Stn. B-1216. 80 p. . Bovey, R. W., H. L. Morton, J. R. Baur, J. D. Diaz-Colon, C. C. Dowler, and S. K. Lehman. 1969. Granular herbicides for woody plant control. Weed Sci. 17:538-541. . Bovey, R. W. and C. J. Scifres. 1971. Residual characteristics of picloram in grassland ecosystems. 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The role of light, concentration, and species in foliar uptake of herbicides in woody plants. ForestSci. 17:164-169. Davis, F. S., M. G. Merkle, and R. W. Bovey. 1968. Effect of moisture stress on the absorption and transport of herbicides in woody plants. Bot. Caz. 129:~183-189. Davis, F. S., R. E. Meyer, J. R. Baur, and R. W. Bovey. 1972. Herbicide concentrations in honey mesquite phloem. Weed Sci. 20:264-267. Fisher, C. E. 1977. Mesquite and Modern Man in Southwestern North America. P 177-188, Chapter 9. In Mesquite - Its Biology in Two Desert Scrub Ecosystems. B. B. Simpson (Ed.). Dowden, Hutchinson 8t Ross, Inc.; Stroudsburg, PA. Fisher, C. E., J. L. Fults, and H. Hopp. 1946. Factors affecting action of oils and water-soluble chemicals in mesquite eradication. Ecol. Monographs 16:109-126. Fisher, C. E., C. H. Meadors, and R. Behrens. 1956. Some factors that influence the effectiveness of 2,4,5- trichlorophenoxyacetic acid in killing mesquite. Weeds 4:139-147. Fisher, C. E., C. H. Meadors, R. Behrens, E. D. Robison, P. T. Marion, and H. L. Morton. 1959. Control of mesquite on grazing lands. Tex. Agric. Exp. Stn. Bull. 935. 24 p. Fisher, C. E., C. H. Meadors, J. P. Walter, J. H. Brock, and H. T. Wiedemann. 1974. Influence of volume of herbicide carriers on control of honey mesquite. Tex. Agric. Exp. Stn. PR-3282. 4 p. Fisher, C. E., H. T. Wiedemann, J. R. Walter, C. H. Meadors, J. H. Brock, and B. T. Cross. 1972. Brush control research on rangeland. Tex. Agric. Exp. Stn. MP-1043. 18 p. Fisher, C. E. and D. W. Young. 1948. Some factors influencing the penetration and mobility of chemicals in the mesquite plant. Proc. North Central Weed Control Conf. 6:197-202. Fisher, C. E. and D. W. Young. 1949. Airplane application of herbicides to mesquite (Prosopis juliflora). North Central Weed Control Conf. Res. Rep. 6:148 (abstract). Fisher, C. E. and D. W. Young. 1949. Cut-surface applications of herbicides to mesquite (Prosopis julifl0ra).North Central Weed Control Conf. Res. Rep. 6:147 (abstract). Haas, R. H., R. E. Meyer, C. J. Scifres, and J. H. Brock. 1973. Growth and development of mesquite. P 10-19. In Mesquite. C. J. Scifres (Ed.). ‘Tex. Agric. Exp. Stn. Res. Monograph 1. Hoffman, G. O. 1975. Control and management of mesquite on rangeland. Tex. Agric. Ext. Serv. MP-386. 15 p. Hoffman, G. O. 1979. Personal communication. Tex. Agric. Ext. Serv., Texas A&M University; College Station, TX. 11 1"" ‘:3; 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 12 ||||||n m: |||u ||||| ||||| um mu ||||| ||||| Illll ||||| ||||| m: |||| ALLIBBB 721,093 Hull, H. M. 1956. Studies on herbicidal absorption and transloca- tion in velvet mesquite seedlings. Weeds 4:22-42. Hull, H. M. 1970. Leaf structure as related t0 absorption of pesticides and other compounds. P 45-93. In Residue Reviews. Vol. 31. F. A. Gunther 6r I. D. Gunther (Eds.). Springer-Verlag; New York, NY. Hull, H. M. and H. L. Morton. 1971. 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Control of woody plants with herbicide mixtures. Weed Sci. 21:423-426. Meyer, R. E. and R. W. Bovey. 1979. Control of honey mesquite (Prosopis juliflora var. glandulosa) and Macartney rose (Rosa bracteata) with soil-applied herbicides. Weed Sci. 27 (In press). Meyer, R. E., R. W. Bovey, W. T. McKelvy, and T. E. Riley. 1972. Influence of plant growth stage and environmental factors on the response of honey mesquite to herbicides. USDA, ARS and Tex. Agric. Exp. Stn. B-1127. 19 p. Meyer, R. E., R. W. Bovey, T. E. Riley, and W. T. McKelvey. 1972. Leaf removal effect after sprays to woody plants. Weed Sci. 20:498-501. Meyer, R. E., H. L. Morton, R. H. Haas, and E. D. Robison. 1971. Morphology and anatomy of honey mesquite. USDA, ARS and Tex. Agric. Exp. Stn. Tech. Bull. No. 1423. 186 p. Morton, H. L. 1966. Influence of temperature and humidity on foliar absorption, translocation, and metabolism of 2,4,5-T by mesquite seedlings. Weeds 14:136-140. Morton, H. L., F. S. Davis, and M. G. Merkle. 1968. Radioisotopic and gas chromatographic methods for measuring absorption and translocation of 2,4,5-T by mesquite. Weed Sci. 16:88-91. Norris, I. I., K. A. Valentine, and I. B. Gerard. 1963. Mesquite control with monuron, fenuron, diuron. New Mexico State Univ., Agric. Exp. Stn. Bull. 484. 14 p. Platt, K. B. 1959. Plant control - some possibilities and limitations II. Vital statistics of range management. I. Range Manage. 12:194- 200. Radosevich, S. R. and D. E. Boyer. 1979. Effect of temperature and photoperiod on triclopyr, picloram, and 2,3,4-T transloca- tions. Weed Sci. 27:22-27. 60. 61. 62. 63. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. Rechenthen, C. A. and H. N. Smith. 1967. Grassland restoration. Part V. Effect of water yield and supply. USDA, Soil Conserv. Serv.; Temple, TX. 4-L-23890. 46 p. Reynolds, H. G. and F. H. Tschirley. 1957. Mesquite control on g6‘ southwestern rangelands. USDA Leafl. No. 421. 8 p. Robison, E. D. 1967. 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Carbohydrate concentrations in honey mesquite roots in relation to phenological development and reproductive condition. I. Range Manage. 28:286-289. Young, D. W. and C. E. Fisher. 1949. Basal application of herbicides to mesquite (Prosopis juliflora). North Central Weed Control Conf. Res. Rep. 6:148 (abstract). Young, D. W. and C. E. Fisher. 1949. Treatments to the foliage of mesquite (Prosopis juliflora) with ground equipment. North Cen- tral Weed Control Conf. Res. Pap. 6:147 (abstract). a [Blank Page in Original Bulletin] Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agricultural Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. v All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, ethnic origin, religion, sex, or age. 1.2M—8-81