Baden» 20.2 l q! g ,6‘? 0QQZ’9)» 0p ' 4k» ' Bindn/eed Control in the ' Panhandle of Texan 14pm’! 1955 TEXAS AGRICULTURAL EXPERIMENT STATION R. D. LEWIS. D |||||| R, C LLLL s: S TTTTT N, TEXAS DIGEST Results of bindweed control experiments at the Amarillo Experiment Station and in surrounding ar-eas since 1949 are reported in this bulletin. Seedling bindweeds have been controlled by cultivation at monthly intervals between crops of wheat or close-drilled sorghum. Patches of bindweed up to one-half acre in size have been eradicated with applica- tions of soil sterilants. Sodium chlorate, Concentrated Borascu, Atlacide, Polybor Chlo- rate and Karmex W proved satisfactory at 5, 16, 7, 12 and and 3/8 pounds per square rod, respectively. Good results with soil sterilants were obtained on dryland when heavy rains fell within a month after the application of the materials. If soil sterilants were not soon leached into the soil the wind frequently blew them away. Applications made in the late summer or early fall are most likelly to be successful since wind movement is low and rainfall is high at that time. Irrigation water was used to leach the soil steril- ants into the soil in some tests. One application of the soil sterilants seldom complete- ly eliminated the weeds; retreatments usually were necessary for complete eradication. Large infestations of bindweed were controlled by intensive cultivation with sweep type plows at 3-week intervals under low soil moisture conditions; cultivations at 2-week intervals were required under good moisture conditions. Sweep-type plows severed all the bindweed tops from the roots and left crop residues on the soil surface to aid in the pre- vention of wind and water erosion. Two annual applications of 1 pound per acre of 2,4-D ester or amine controlled weeds on areas where cultivation was not feasible, such as road- sides, grass waterways, pastures and ranges”? l,‘ The most satisfactory method of bindweed control on large acreages of cropland was through competitive cropping, intensive cultivation and the use of 2,4-D. Wheat was the best competitive crop used. Sorghum was not established easily during the summer when the weeds were growing vigorously. A fallow-wheat system, using intensive cultivation during the fallow periods, gave good control. eliminating 92 percent of the weeds in 3 years. Continuous cropping to wheat was a good practice for controlling bindweed when used with. intensive summer cultivation and 2,4-D in the fall before wheat was planted, or in the spring when the wheat was fully tillered. CONTENTS Page Digest ............................................................................................................................................................................. .. 2 Introduction ............................................................................................................................................. ------------------- -_ 3 Description of Bindweed ............................................................................................................................................ -- 3 Experimental Methods ................................................. ........................................................... ______________________________ _- 4 Results ......... ............................................................................................................................................................... -- 4 Bindweed Seedling Infestation and Control. ..................................................................................................... ._ :1 Eradication of Small Patches of Bindweed .......................................................................................................... -- 5 Application to Dryland ........................................................................................................................................ -- 5 Application to Irrigated Land ........................................................................................................................... _. 6 Control of Large Infestation ................................................................................................................................. .. 6 Intensive Cultivation ........................................................................................................................................... .. 6 2,4-D and Related Compounds .......................................................................................................................... .. 7 Cropping Systems with Competitive Crops ...................................................................................................... _. 7 Literature Cited ...................................................................................................................... .._. ................................... .. 3 Bindweed Control in the Panhandle of T exas A. F. WIESE and H. E. REA* IELD BINDWEED (Convolvulus arvensis), A NA- TIVE 0f Europe, was introduced into North America along the Atlantic seaboard and was _ reported in Virginia as early as 1739. It spread westward across the United States, and by 1900 was established in most of the Western States (5) . At present, 32,000 acres of the weed occur in the ,Panhandle of Texas on 28 percent of the farms, threatening crop production on over a million and a half acres of cultivated land. Control methods for bindweed were sugges- ted as early as 1909 by Cox (2). The first re- search for bindweed control in Texas was conduc- ted by S. E. Wolf at the Blackland Experiment Station at Temple over 25 years ago. The research reported in this bulletin was started at the Amarillo Experiment Station and surrounding areas in 1949. The soil type on the station is Pullman silty clay loam, a reddish-chest- 311111; soil. This soil has 45 percent clay in some layers. The organic matter content of the crop- land is about 2 percent and the pH of the surface soil is approximately 6.5. The soil is highly cal- careous and overlays caliche (CaCog) at a depth 0f 4 to 6 feet on level land (1). Since 1938, the average annual rainfall on the Amarillo station has been 18.44 inches. During the experimental period reported here, the rain- falllvaried from 24.52 inches in 1949 to 14.77 in- ’ aches in 1952. Monthly rainfall from 1949 through 1953 is shown in Table 1. Heavy greenbug infes- tations in 1950 and 1951, and the low rainfall in 1952 severely reduced dryland crop production during the investigations. ‘Respectively, assistant agron.omist, Amarillo Experiment ‘Station, Bushland, Texas, and associate professor, De- partment of Agronomy, College Station, Texas. TABLE 1. MONTHLY RAINFALL IN INCHES AT THE AMA- RILLQ EXPERIMENT STATION, 1949-53 uebib 1040 1050 1051 1052 1050 Iunuary 1.01 '1' 0.50 0.40 0.40 February 0.00 0.00 0.00 0.11 0.02 larch 0.00 o 0.70 0.70 0.41 f April 2.05 0.00 0.10 2.97 0.10 Hay 0.00 1.12 0.25 1.40 0.01 iebe 0.45 5.05 0.00 2.00 0.00 My 0.10 0.00 2.40 2.04 4.04 1109001 1.04_ 2.10 2.17 2.00 2.70 September 2.51 0.00 0.00 0.00 0.54 l Dciober 1.17 0.11 1.20 o 5.10 .~ llevember o 0.02 0.20 1.04 0.00 l December 0.40 0.21 0.20 0.40 0.04 24.52 20.30 19.31 14.77 16.11 Figure 1. Bindweed growing in a field near Bushland. DESCRIPTION OF BINDWEED Field bindweed, sometimes called possession vine, is a hardy, climbing perennial with arrow- shaped leaves and trumpet-shaped flowers (Fig- ure 1). The plant is a trailing vine that grows along the ground, but climbs readily if supported. The stems may be as long as 3 feet (5). The leaves are pointed at the tip and have large point- ed basal lobes; however, their shape and size may vary considerably (Figure 2). The flowers are about three-fourths to 1 inch in diameter, varying from white to pink. In Northwest, Texas, the plant usually starts bloom- ing in late May or early June and continues to Figure 2. Bindweed leaves showing variations in size and shape. r /‘-. i’: 1"! A I" 221.1412) 0 Figure 3. Bindweed seed and pods in relation to wheat seeds. flower and set seed throughout the summer as long as moisture is available. One to four seed are formed in each pod. The seed are about the size of a wheat kernel and have a pebbled, black seed coat (Figure 3). Water cannot enter the coat readily to start growth and many of the seed remain dormant for long periods of time. Seed production is favored by warm, dry weather (5) ; consequently, seed set is usually very high in the Texas Panhandle. Seed. samplings taken near Bushland in 1954 showed over one-half million bindweed seeds per acre were produced in Wheat, Figure 4. Bindweed seedlings. and up to four and one-half million seeds per acr i were formed in bindweed-infested road ditches. The root system of bindweed is very exten sive and contains food material which can su port the plant for a long period. In the Panhandl area, the roots extend to the caliche, which varie In deep soils, roots hav from 4 to 6 feet deep. been found at depths of more than 20 feet (4). Bindweed seedlings can be distinguished b their heart-shaped cotyledonary leaves (Figur 4). The young seedling develops a deep tapro and in about 11 weeks spreads radially by pro ducing lateral roots. New plants are produc from buds on the lateral roots and, within o ~ a season, a plant may spread up to 10 feet in dia . eter (3). a EXPERIMENTAL METHODS The experiment was planned to study bin weed seedling infestation and control, to dete mine the best method for eradication of bindwe patches up to one-half acre in size and to fi practical methods for the control of larger infe tations of the weed. Studies with soil sterilan for eradication of small patches under dryla conditions were carried out near Bushland, Clau and Dumas. Similar work under irrigated cond I tions was conducted near Summerfield and Bus land. Methods of control for large infestations we tested on 40 acres of land near the Amarillo E periment Station at Bushland. Control metho tested were intensive cultivation, 2,4-D applic tions and cropping systems using wheat and so ; ghum as competitive crops. RESULTS Bindweed Seedling Infestation and Control Most bindweed patches on cropland are sta ted from seed carried to the land in infested gra seed, dirty combines or by cattle eating conta I nated feed. Because of this hazard, only clei seed should be used in planting grain seed '1 combines should be cleaned carefully after wor ing in bindweed-infested fields. Grain contai a ing bindweed seed should be ground before it fed. These simple practices would prevent mu of the spread of bindweed to clean fields. Dormant bindweed seed remaining in ; a soil on areas where the weed has been eradicati can germinate and become established if the se lings are not controlled. An average of 162 se per square yard of soil 6 inches deep was fou in plots at Bushland after the bindweed had be . controlled by 4 years of intensive cultivation. T following spring, 2 seedlings per square yard gr A on the same plots and_ had to be controlled to p vent reinfestation. In Kansas, bindweed se lings emerged on land 30 years after the origi infestation of the weed was controlled. Seedlin were controlled by using monthly cultivations t. tween crops of winter wheat or closely-drilled ~ p FPTBUOMHmr+r~ mv-aa-L ghums. Sorghum planted in 40-inch rows with monthly cultivations between crops showed slow bindweed reinfestation. Normal cropping prac- tices without monthly cultivations in either wheat or closely-drilled sorghum did not control the seed- lings. Return of previously-infested areas to per- ennial grasses also showed bindweed Would rein- fest the land (9). Eradication of Small Patches oi Bindweed Since small infestations of bindweed should be eradicated before they spread, investigations with soil-sterilizing herbicides have been made since 1949 at Claude, Dumas, Bushland and Sum- merfield. Experiments were conducted und.er both dryland and irrigated farming conditions with sodium chlorate, Concentrated Borascu, At- lacide, Polybor Chlorate and Karmex W. Sodium chlorate has been used for bindweed control since 1927, when Latshaw and Zahnley (6) first tested the material. It is very soluble in water and can be applied either as a spray or dry with a mechanical spreader. The chlorate ion is the toxic agent in this material. Organic matter sprayed with sodium chlorate is highly inflammable upon drying and should be handled with the same precautions as gasoline. Clothing impregnated with sodium chlorate ignites easily. Because of this hazard, all applications of the material should be made dry with a mechanical ‘spreader. Animals may eat enough soduim chlo- rate to poison themselves; consequently, cattle should not have access to chlorate-treated areas until the material has been leached into the soil (7). Concentrated Borascu is an insoluble form of borate and must be applied dry with a mechan- ical spreader. Although small quantities of boron are required for plant growth, high concentra- tions will kill most vegetation. The material is iioninflammable and nonpoisonous and can be used Cwhere cattle are grazing. Atlacide is a chlorate type soil sterilant that may be applied dry or as a spray. It is less haz- ardous than pure sodium chlorate, but the same precautions should be used as for sodium chlo- rate. Polybor Chlorate is a mixture of sodium pen- taborate and sodium chlorate. It is soluble and can, be applied as a spray or in dry form. The material is very fine and, when applied dry, is Tgsily blown away. Karmex W (3-p-chlorophenyl 1, 1-dimethyl ma) is an organic chemical and is extremely fixic to plant growth. It must be applied as a ay, using about 1 gallon of water per square . Plots of soil treated with Karmex W in 1951 _ are free of vegetation. Because vegetative fwth may be prevented for a long time, Kar- x W should be applied only to areas where a ‘g period of soil sterility would not be objec- nable. TABLE 2. AVERAGE RAINFALL AND CONTROL OF FIELD BINDWEED AT DUMAS AND CLAUDE IN 1950 USING 3 POUNDS OF SODIUM CHLORATE PER SQUARE ROD Month Rainfall, inches Percent control April 2.00 79 May 0.77 38 lune 3.94 90 August 3.13 97 September 3.99 86 October 0.36 59 November 0.20 79 Application to Dryland Investigations to determine the most effec- tive rate and time of application of the soil ster- ilants to dryland areas were conducted during 1949, 1950 and 1951. The most economical rates in pounds per square rod were: sodium chlorate, 5; Concentrated Borascu, 16; Atlacide, 7; Poly- bor Chlorate, 12; and Karmex W %. The most satisfactory time of application varied with the amount of rainfall that followed the application of the herbicides. If heavy rains fell within a few months after the application, satisfactory re- sults were obtained. As can be seen in Table 2, using sodium chlorate as an example, the best con- trol was obtained in June, August and Septem- ber 1950 when at least 3 inches of rain fell dur- ing each month. Very poor control was obtained when the rainfall was low during the month of application. If rainfall did not leach the soil ster- ilants into the soil, the wind frequently blew them away. This is particularly true of fine materials such as Polybor Chlorate and Atlacide. Because applications of soil sterilant are more successful during periods of low wind movement and high rainfall, late summer or early fall treatment are most likely to give satisfactory bindweed eradi- cation. This can be seen in Table 3, which shows the average wind movement and rainfall at the Amarillo Station since 1939. One application of soil sterilants usually does not completely eliminate the bindweed. The re- maining plants should be spot-treated about 2 years after the first treatment. If more than 50 plants per square rod remain, spot retreatment will be impractical and the entire area should be treated again with the soil sterilant (8). The soil sterilant should be spread at least 10 feet be- yond the edge of the patch in order to kill all of the roots. After sterilants have been applied, the land should not be disturbed for at least 1 year. This will allow the sterilants enough time to leach TABLE 3‘. AVERAGE WIND MOVEMENT AND RAINFALL AT THE AMARILLO EXPERIMENT STATION, 1939-53 Month Wind, mph. Rainfall. inches Ianuary 6.99 0.55 February 7.88 0.38 March 8.76 0.41 April 8.54 1.30 May 7.69 2.91 Iune 7.58 2.53 Iuly 6.30 2.51 August 5.99 2.57 September 6.63 1.68 October 6.14 2.14 November 6.31 0.75 December 6.54 0.71 uniformly into the soil. Lister cultivation should not be used for 2 or 3 years following the appli- ' cation because the lister blades may go deeper than the sterilants have penetrated, allowing the weeds to grow in the bottom of the lister furrows. Application to Irrigated Land Irrigation water can be used to leach the soil sterilants down to the plant roots. If the patch covers 10 or more square rods, the area should be bordered and then flooded with 3 or 4 inches of water (Figure 5). If it does not rain within a month following the first application of water, a second application will speed up the results. Even on clay soils, the sterilants will be leached too deeply for maximum results if more than 4 in- ches of water are used. The land should not be disturbed after flooding. The remaining plants should be retreated and the area reflooded 1 year after application. If the Jinfested spots are less than 10 square rods, bordering the area is inconvenient. The best method is to apply the soil sterilants just before a regular irrigation (Figure 6). When using this method to leach the sterilants into the ‘soil, culti- vations after application of the sterilants may re- duce the effectiveness of the soil sterilants. As a result, several retreatments may be necessary to eliminate the weeds. Sodium chlorate, Polybor Chlorate and Atlacide, the more soluble materials, will not be distrubed as much by cultivation as other soil sterilants because they are easily leach- ed into the soil. Figure 5. Bindweed in this spot was eradicated by bordering. applying a soil sterilant and 4 inches of irrigation water. Figure 6. Bindweed in this spot was eradicated by applying a soil sterilant iust before a regular irrigation. Caution: Do not use Karmex W on irrigat land unless it is applied in a bordered area becau it may move with irrigation water and kill a 1 nual crops in other parts of the field. This ha 1 ard does not exist with other soil sterilants whic leach into the soil where they are applied. Control oi Large Infestations _ Because it is too expensive to eradicate lar infestations of bindweeds with soil sterilant y cheaper methods of control have been teste These were intensive cultivation, the use of 2,4- ~ and cropping systems with competitive crops. Intensive Cultivation Perennial weeds, such as bindweed, are kill with cultivation by gradually depleting the fo supply in the root system. Each time the we‘ grows after it has been cut off by cultivatio a food material must be transported from the roo to the growing area near the soil surface. As result, repeated cultivations cause a depletion o_ food reserves. A sweep-type cultivator should used to be certain that the plant tops are sever from the roots. With repeated sweep cultiv tions, crop residues are conserved and left on t . soil surface, greatly reducing the hazard of wi . and water erosion. Figure 7 shows the sweep plo I used for bindweed cultivations during these tes One-way plows, disk harrows, lister plows and o, weeders tend to cover weeds instead of cutti them off, and the root reserves of the plants a not reduced. Bindweed also escapes cultivati with a sweep plow if the shovels do not ha enough overlap. - All cultivations in the experiment at Bush- a land were made at 4 inches, the most economical depth of cultivation (8). Weeds were cultivated every 9 and 15 days after emergence throughout the growing season. . Both treatments gave 89 percent control in 3 years (Table 4). The first cultivation in the spring was given between April 15 and May 1, when the bindweed runners were . about 4 to 6 inches long. The last cultivation in the fall depended on moisture conditions and var- iedfrom September 24, 1952 (a dry year) to No- vember 10, 1949 (a wet year). The average num- ber of annual cultivations for the 9 and 15-day cultivation intervals was 6.3 and 5.5, respectively. average time between the cultivations was 29 days, respectively. The number of days .- cultivations varied with moisture condi- ” . During wet periods, the weeds emerged in adu 4 days after cultivation; during very dry times, the weeds required 30 or more days to reach the soil surface. A practical approach for using an intensive cultivation control program would be to cultivate every 3 weeks. If growing conditions are favor- able, cultivations at intervals of 2 weeks are re- quired. However, if it is dry and the bindweed has not emerged in 3 weeks, cultivation should be delayed until after the weeds have emerged. 2.4-D and Related Compounds Successful control of bindweed with 2,/1-D (derivatives of 2A-dichlorophenoxyacetic acid such as the ester and amine salts) depends on the size and rate of growth of the plant at the time of treatment. Experimental work conduc- ted in 1953 indicates that bindweed runners must . be at least 6 to 10 inches long and growing vigor- ously before good root kill can be obtained with 2,4-D. Top kills will not control the weeds for long periods. Various formulations of 2,4-D, MCP and 2,4,5-T were tested for bindweed control at one- half and 1 pound per acre. 2,4-D gave better c011- . trol than MCP and 2,4,5-T. During wet periods, l the one-half-pound rate of 2,4-D acid gave as much control as the 1-pound rate, but during dry periods when growth was somewhat restricted, a the 1-pound rate was more effective. The ester , ‘formulation of 2,4-D usually resulted in greater A stand reduction than the amine formulation the first time the chemicals were applied. Both for- mulations gave the same degree of control when several applications were used. Table 5 shows that two annual applications of 2,4-D ester or amine at 1 pound per acre for 3 years, timed in TABLE 4. PERCENT BINDWEED CONTROL, NUMBER OF ANNUAL CULTIVATIONS AND DAYS BETWEEN I CULTIVATIONS ACHIEVED WITH INTENSIVE CULTIVATIONS AT 9 AND 15 DAYS AFTER - WEED EMERGENCE lgeriod of Percent control Annual bggiin I‘ cultivation after 3 years cultivations cultivations o ldays after emergence 89 6.3 23 l5 days after emergence 89 5.5 29 TABLE 5. BINDWEED CONTROL AFTER 3 YEARS OF TREATMENT ON NONCROPPED LAND USING 1 POUND PER ACRE OF 2,4-D ESTER AND AMINE . . Percent control Annual Herblclde after 3 years treatmentsl 2.4-D amine 73 2 2.4-D ester 8U 2 1 2.4-D was applied to the plots when sufficient weed growth made spraying feasible. accordance to the growth of the bindweed, gave 8O and 73 percent control respectively. This was about the same amount of control that was ob- tained with intensive cultivation. Repeated 2,4-D treatments at 1 pound per acre are a practical method of controlling bindweed in areas that can- not be cultivated, such as pastures, ranges, grass waterways and road ditches. 2,4-D also can be used effectively with intensive cultivations on cropland when growing conditions are good. Cropping Systems with Competitive Crops Using a competitive crop in a bindweed con- trol program is the economical method of con- trolling‘ this weed. The crop produces an income from the land while the weeds are being controll- ed and the crop residues produced help control wind and water erosion. Several cropping systems using wheat as a competitive crop have been satisfactory for bind- weed control (Table 6). Alternate fallow and wheat was the most successful method, giving 92 percent control after 3 years of treatment. During the fallow period, cultivations were made every 9 days after weed emergence. The first year of cultivation usually controlled the weeds well enough to prevent a yield reduction in the next wheat crop. This yield increase usually paid for the extra tillage in the intensive cultivation program. Continuous wheat production with in- tensive cultivations 9 days after the bindweed emerged between crops was not satisfactory, giv- ing only 68 percent control in 3 years. 2,4-D ap- plied in the spring at one-half pound per acre to wheat at the full tiller stage, preceded by inten- a ifism e..- Figure 7. One type of sweep plow suitable for intensiv cultivation in a bindweed control program. 7 Figure 8. _ Sorghum plot (left) infested with bindweed, and a wheat plot (right) relatively free oi bindweed. Both areas have had cultivations for 5 years every 9 days aiter weed emergence when the land was not in crop. sive cultivation, increased the control from 68 to 85 percent. A 2,4-D treatment at t1 pound per acre, applied in August to land used. for annual wheat crops after intensive cultivations in July, increased the control to 88 percent. This treat- ment was not very effective during years when it was too dry for good weed growth; it was very effective during years with a wet August. The 2,4-D should be applied at least 3 Weeks before wheat is seeded, since the chemical may cause injuryto the germinating wheat. This also al- lows the 2,4-D enough time to move into the weed. roots. Wheat is a better competitive crop than sor- ghum. Wheat becomes established in the fall and winter while the weeds are dormant, and can compete for moisture in the spring. Sorghum planted in June while the bindweed is growing vigorously is unable to compete for the limited supply of water? (Figure 8). * A practical method to controlilarge areas of . bindweed on Pullman soils is to use alternate wheat and fallow with sweep-type tillage during the fallow periods. A wheat, fallow, wheat rota- tion gives the best bindweed control, and is one of the most economical cropping systems for the TABLE B. BINDWEED CONTROL IN WHEAT USING INTEN- SIVE CULTIVATION 9 DAYS AFTER BINDWEED EMERGENCE, WITH AND WITHOUT ZA-D AP- PLICATIONS a Percent control Cultivations Sprays Treatments after 3 years annually annually Fallow-wheat-iallow 92 6 U Continuous wheat. cult. Iuly. ZA-D Augfi- 3 l Continuous wheat, cult. Iuly. Auger SQPtn 2|4'D 4 1 Continuous wheat. cult. Iuly. Aug.. Sept. 68 5 0 1 One pound of 2.4-D ester per acre to the bindweed during August. 2 One-half pound oi 2.4-D ester per acre when the wheat was fully tillered in the spring. 8 area (10). During the fallow periods, cultiva- tions should be made at 3-week intervals unless moisture conditions induce rapid weed growth. I this happens, the bindweed should be allowed t grow until the runners are 6 to 10 inches lon and then be treated with 1 pound of 2,4-D aci per acre. After the 2,4-D treatment, cultivation will not have to be resumed until after the weedi reemerge. Treatments of 2,4-D during wet per iods reduce the number of cultivations necessar p and save crop residues. If the bindweed threa ens to produce seeds in the wheat during th spring, one-half pound of 2,4-D acid per acr should be appled to the wheat before it reache the boot stage. e LITERATURE CITED 1. Coover, J. R., Van Doren, C. E. and Whitfield, C. J Some characteristics of the Pullman soils on the Am arillo Experiment Station. Texas Agricultural Expe: yment- Station Misc. Pub. 97. 1953. 2. Cox, H. The eradication of bindweed or wild morn ing glory. USDA Farmers Bul. 368. 1909. 3. Frazier, J. C. Nature and development of the ro system of Convolvulus arvensis. Bot. Gaz. 104:417 425. 1943. - 4. Principal noxious weeds of Kans with emphasis upon their root systems in relation control. Kan. Agr. Exp. Sta. Bul. 331. 1948’. I 5. Kiesselbach, T. A., Peterson, N. F. and Burr, W. "* Bindweeds and their control. Nebr. Agr. Exp. S Bul. 287. 1934. v 6. Latshaw, W. L. and Zahnley, J. W. Experimen with sodium chlorate and other chemicals as herb cides for field bindweed. Jour. Agr. Res. 35:757-76 1927. 7. Raynor, R. N. and Britton, J. W. Toxicity of herb A cides to livestock. California Agriculture, Califo Agricultural Experiment Station. Berkeley 4, Cal fornia. November 1943. 8. Timmons, F. L. Results of bindweed control expe 5 ments at the Fort Hays Branch Station, Hays, Ka sas, 1935 to 1940. Kan. Agr. Exp. Sta. Bu.1. 296. 194 9. .............................. -- Duration of viability of bindwe, seeds under field conditions and experimental resul in the control of bindweed seedlings. Agron. Jou 41:130-133. 1949. ‘ 10. Van Doren, C. E. and Johnson W. C. Fallow and t wind erosion hazard. SCS-TP-lll. 1952.