5-1568 April 19a? JUN o <2 1987 ‘ i 199s [MM Universjiav ontrolling Weeds & Volunteer Crops During Fallow Periods THE TEXAS AGRICULTURAL EXPERIMENT STATION/ Neville P. Clarke, Director/ The Texas A&M University System/College Station, Texas Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . .2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Pigweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Barnyardgrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Witchgrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 “ Stinkgrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Volunteer Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Volunteer Barley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Volunteer Sorghum . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Volunteer Corn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 COVQI‘ P110“)? Kill 0f fully tillered Wheat when Sprayed Keywords: Pigweed/barnyardgrass/witchgrass/stinkgrass/ with 0.25 pounds per acre of glyphosate in 7 gallOnS wheat/barley/corn/sorghum/glyphosate/paraquat/con- t“ per acre of spray carrier. trolled droplet applicator. Controlling Weeds ‘and Volunteer Crops During Fallow Periods A. F. Wiese and E. W. Chenault Professor and Research Associate The Texas Agricultural Experiment Station Bushland, Texas Summary Because postemergence herbicides are the heart of most no-tillage systems, research has been conducted since 1978 to determine the lowest rates of paraquat (1,1’—dimethyl-4,4'-bipyridinium ion), glyphosate ml-(phosphonomethyl)glysine], and other herbicides to kill common annual weeds and volunteer crops during fallow periods between crops. Using carrier volumes of 7 gallons per acre (gpa) with fan tip nozzles and 3 gpa or less with a controlled droplet applicator (CDA) increased weed control compared to using 26 gpa of carrier. The best control with the two herbicides occurred when small weeds growing in wet soil were sprayed. Pigweed (Amaranthus palmeri S. Wats.) that were 1.5 inches tall or less were controlled with 0.12 pounds per acre (lb/A) paraquat or glyphosate. With 2- inch pigweed, paraquat at 0.25 lb/A and glyphosate at 0.19 lb/A were required to give 90 percent or more control when applied with a CDA. By comparison, the minimum effective rate for the two herbicides was 0.5 lb/A when 26 gpa of carrier volume was used. Barnyardgrass [Echinochloa crus-galli (L.) Beauv] that was 3 to 6 inches tall and under stress for moisture was not controlled with paraquat at 0.25 lb/A with any amount of carrier. Glyphosate at 0.19 lb/A applied with fan nozzles at 7 gpa or a CDA at 1.2 or 0.55 gpa carrier volume gave over 90 percent control of the barnyardgrass. With carrier volumes of either 3 or 26 gpa, control of witchgrass (Panicum capillare L.) or stinkgrass [Eragros- tis cilianensis (All.) E. Mosher] was accomplished with 0.25 lb/A glyphosate. Paraquat at 0.25 lb/A only con- trolled witchgrass when applied at 3 gpa of carrier through a CDA. Small volunteer wheat (Triticum aes- tivum L.) and barley (Hordeum vulgare L.) were con- trolled with paraquat and glyphosate each at 0.25 lb/A. Glyphosate at 0.25 lb/A controlled small volunteer sorghum [Sorghum bicolor (L.) Moench] and corn (Zea mays L.). Introduction No-tillage leaves crop residues on the soil surface, thus offering the greatest potential for reducing soil erosion and conserving soil water of any innovation in the 20th century. In order for no-tillage systems to be successful, herbicides must control weeds in both crops and fallow periods (Wiese and Staniforth 1973). Control of weeds and volunteer crops with herbicides must be at the lowest possible rates of herbicide to compete with conventional tillage before no-tillage can be adopted. The purpose of these studies was to evaluate several herbicides, volumes of herbicide spray carrier, and additives to find the lowest possible rate for controlling with postemergence herbicides the annual weeds that grow during fallow periods in no- tillage systems in the Southern Great Plains. Materials and Methods Studies to control annual weeds and volunteer crops during noncrop periods were conducted at the U.S. Department of Agriculture Conservation and Production Research Laboratory, Bushland, Texas from 1978 through 1983. The soil was Pullman clay loam (fine, mixed, thermic family of Torrertic Paleus- tolls, order Mollisols), with equal parts of sand, silt, and clay; 1.5 percent organic matter; and a pH of 6.5 at the soil surface (Mathers, et al. 1963). Since 1979, pigweed [primarily Amaranthus palmeri S. Wats. and A. hybridus (L.)], barnyardgrass [Echinochloa crus-galli (L.) Beauv.], witchgrass (Panicum capillare L.), and stink- grass [Eragrostis cilianensis (All.) E. Mosher] have been sprayed at various stages of growth. Visual plant vigor ratings at treatment which reflected soil water condi- tions were excellent, good, fair, or poor. Volunteer stands of winter wheat (Triticum aestivum L.), winter barley (Hordeum vulgare L.), sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.) also were sprayed. Herbicides used and rates applied are shown in subsequent tables. Additional information includ- ing trade name and manufacturer is in the Appendix. In some studies, herbicides were sprayed at 26, 7, 3, 1.2, or 0.55 gallons per acre (gpa) of spray carrier. The 26 and 7 gpa volumes were obtained with tapered fan nozzles operated at 30 pounds per square inch (psi) and at a speed of 3 miles per hour. The three lowest volumes were applied through controlled droplet applicators (CDA). From 1978 through 1980, a hand held ”Herbi" was used for CDA application, and after that, a ”Micro Max" was used.1 Both CDA’s generated droplets 250 microns in diameter. All applications except with the ”Herbi” were made with applicators mounted on a small tractor. Spray additives were used with most treatments, and amounts are shown in the tables. Additives used were X-77 (alkylaryl polyoxy- 1”Herbi" and ”Micro Max” are products of the Micron Corporation, P.O. Box 19698, Houston, Texas 77024. 2 ethylene glycols free fatty acids and isoproponal), Ag 98 (alkylaryl polyoxyethylene glycols), WK (trimethyl- nonyl polyethoxyethanol), 411F type crop oil concen- trate (COC), and a cotton oil based product with 9x percent emulsifier. Plot size varied from 5 to 15 feet wide and 25 to 75 feet long. In all studies, treatments were replicated three times in a randomized block design. Mean significance was tested with a combina- tion of analysis of variance and the least significance difference at P = 0.05. ' Results Pigweed Results from seven studies conducted on pigweed since 1978 are given in Tables 1 through 5. Three studies were conducted comparing carrier volumes of 26 and 3 gpa with several rates of paraquat and glyphosate (Table 1). Pigweed size varied from 6 to 30 inches and the weeds were growing vigorously with good soil moisture. Control was markedly better with 3 gpa of carrier than with 26 gpa. Six-inch weeds were a little easier to control than larger weeds, especially with 26 gpa of carrier. Two-inch pigweed were easy to control with paraquat or glyphosate (Table 2). Percent control exceeded 92 percent with 0.25 lb/A of either paraquat or glyphosate sprayed with either 3 or 7 gpa carrier. In another study, paraquat and glyphosate each at 0.18 and 0.25 lb/A were applied in late Iune to pigweed that were 2 to 4 inches tall with poor growth because the soil moisture level was approaching the wilting point. Carrier volume varied from 0.55 to 26 gpa (Table 3). A cotton-based oil additive containing 7 percent emulsifier was compared to Ag 98 surfactant. There was not a consistent difference among the additives. As carrier volume was reduced, control of pigweed increased. Paraquat gave some initial burn of pigweed leaves 6 days after treatment, but this result did not persist. About 5 weeks after application, effects of paraquat on the pigweed had disappeared from all carrier volumes except 0.55 gpa (Table 3). Control with glyphosate was better with 7, 1.2, and 0.55 gpa of carrier than with 26 gpa carrier. In a fourth study, several different herbicides were applied with 26 gpa carrier to pigweed at three stages of growth (Table 4). Pigweed were germinated with an irrigation about September 1. By September 7, they A had two true leaves, and 5 days later were 1.5 inches tall with excellent or good vigor. A week later, pigweed were 6 inches tall and had dried out the soil and were in poor growing condition. Timing of application was critical. Control of small pigweed that had two true leaves or were 1.5 inches tall was excellent with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile). It took 0.25 lb/A to eliminate the pigweed with two true leaves, but 0.38 lb/A was required to eliminate 1.5-incl! pigweed. Only bromoxynil at 0.5 lb/A gave 8O percent i’ control of 6-inch pigweed under dry conditions. The nkl Table 1. Effect of carrier volume on control of pigweed with paraquat and glyphosate Percent pigweed control by year Herbicide plus Herbicide Carrier additive rate volume 1978 1980 1982 (lb/ A) (gpa) Paraquat + 0.25 3 100 83 86 0.5% sa 0.5 10o 97 95 1.0 100 100 99 Glyphosate + 0.25 100 99 95 0.5% S 0.5 100 99 99 1.0 100 99 — Paraquat + 0.25 26 23 20 37 0.5% S 0.5 8O 68 72 1.0 91 95 92 Glyphosate + 0.25 65 17 34 0.5% S 0.5 100 58 83 1.0 100 99 100 131110.05 20 13 9 Pigweed height, inches 6 10 30 Plant vigor good good excellent Application date 8-31-78 8-12-80 7-9-81 Evaluation date 9-12-78 9-8-80 8-6-81 aS = Surfactant and was either X-77 or WK. pigweed, 1.5 inches or less, also were controlled at 94 percent or more with paraquat, sulfosate (trimethyl- sulfonium carboxy methylamino methylphospho- nate), and glyphosate each at 0.12 lb/A. Fomesafen (5- [2-chloro-4-(trifluoro—methyl)phenoxy]-fl-(methyl- sulfonyl)-2-nitrobenzamide) gave 90 percent or more control of small pigweed at 0.12 lb/A. Fenoxaprop ( i )- 2-[4[(6-chloro-2-benzoxazolyl)oxy]phenoxy]pro- panoic acid) and dimethylamine salt of dicamba (3,6- dichloro—2—methoxybenzoic acid) gave 76 percent or less control at 0.12 lb/A. Another study compared several herbicides for con- trol of 4-inch pigweed and 5-inch barnyardgrass with poor vigor (Table 5). The following herbicides were applied in 26 gpa of spray carrier: fluazifop (( i )—2-[4- [[5—trifluoromethyl)-2-pyridinyl]oxy]phen0xy]pro- panoic acid), sethoxydim (2-[1-(ethoxyimino)butyl]-5- [2(ethylthio)propyl]-3-hydroxy—2—cyclohexen-1-one), haloxyfop (2-[4—[[3-chloro—5-(trifluoromethyl)-2- pyridinyl] oxy]phenoxy] propanoic acid), quizalofop (2-[4-[(6-chloro-2-quinoralinyl) oxy]phenoxy]-propio- ' nic acid, ethyl ester), glyphosate, paraquat, sulfosate, and fenoxaprop. Rates varied from 0.18 to 0.25 lb/A and each herbicide was applied alone or tank mixed with 1.0 lb/A 2,4—D ester. The 2,4-D with glyphosate, sulfosate, or fenoxaprop effectively controlled pig- weed, but control of barnyardgrass was 8O percent or less with herbicides other than glyphosate. Adding 2,4-D to sulfosate and glyphosate did not enhance pigweed control. Adding 2,4—D to fenoxaprop did not -\improve pigweed control and control of barnyard- grass was unsatisfactory with or without 2,4-D. Add- ing 2,4-D to paraquat improved pigweed control, but control of drought stressed barnyardgrass was poor. Table 2. Effect of carrier volume on control of small pigweed with paraquat and glyphosate Percent pigweed control at two carrier volumes Herbicide plus Herbicide additive rate 3 gpa 7 gpa (lb/A) Paraquat + 0.5% X-77 0.19 93 — 0 25 97 98 0 38 100 100 0.5 — 100 Glyphosate + 0.5% X-77 0.19 72 — 0.25 92 99 0.39 — 99 0.5 100 100 LSD 0.05 8 Pigweed height, inches 2 Plant vigor fair - "- Evaluation date 8-13-82 - Scoring date 8-25-82 - Barnyardgrass Control of 3- to 6-inch barnyardgrass growing in dry soil with poor vigor was attempted with paraquat and glyphosate at 0.18 and 0.25 lb/A applied in carrier volumes of 26, 7, 1.2, or 0.55 gpa (Table 6). The cotton oil additive was compared to Ag 98 surfactant at all levels of carrier volume. There were no consistent differences among additives. Control with the two herbicides applied in a carrier volume of 26 gpa was 3 not above 66 percent 5 weeks after treatment. With the exception of a carrier volume of 0.55 gpa, all leaf burn from paraquat had disappeared 5 weeks after applica- tion. Glyphosate at 0.25 lb/A, on the other hand, gave 95 percent or more control at carrier volumes of 7 gpa or less at the final evaluation date. Witchgrass Excellent control of large mature witchgrass was obtained with glyphosate at 0.12 lb/A applied in 3 gpa of carrier volume regardless of plant vigor. If plant vigor was fair, but not poor, 0.12 lb/A of glyphosate killed witchgrass when applied in 26 gpa of carrier volume (Table 7). At 26 gpa, 0.25 lb/A of glyphosate gave 95 percent or more control in each of 2 years. Paraquat at 0.25 lb/A gave excellent control the year when soil moisture and plant vigor were fair, but failed when the soil was dry. MSMA gave excellent control of witchgrass at 2.0 and 4.0 lb/A irrespective of carrier volume or soil moisture. Stinkgrass Glyphosate controlled stinkgrass at 0.25 lb/A (Table 7). Paraquat and MSMA failed regardless of applica- tion rate. Herbicides were applied in a carrier volume of 26 gpa. x4 Volunteer Wheat In 1978, 1982, and 1983, paraquat and glyphosate were applied to wheat in either 26 or 3 gpa of spray carrier (Table 8). In two of the five experiments, carrier volume of 7 gpa also was compared. In 1978 and October 1982, 3 gpa applied with a CDA and 26 gpa applied with fan nozzles were compared on small wheat that had not been tillered. In each case, the lower amount of carrier resulted in more kill of wheat at the same rates of paraquat or glyphosate. In August 1982 when 3 and 7 gpa were compared, the 7 gpa carrier volume was comparable or better than the lower carrier volume. Once wheat had tillered, there was not a marked difference in volume of carrier. If wheat had jointed, application at 3 gpa with a CDA was not effective. Control was much better with either paraquat or glyphosate applied in 7 or 26 gpa; howev- er, control with the herbicides at this stage was not as good as when smaller wheat was sprayed. Herbicides (C 1 Table 3. Pigweed control with paraquat and glyphosate applied in several carrier volumesa Carrier volume (gpa) Herbicide Additive Herbicide rate and rate 26 7 1.2 0.55 (lb/ A) Percent pigweed control 6 days after treatment Glyphosate 0.1a Oil1 qt/Ab 1s 7s 99 99 Oil 2 t/A 8 76 99 — Ag 98 28 86 99 99 Glyphosate 0.25 Oil 1 qt/A 13 46 98 93 Oil 2 qt/A 18 37 100 — Ag 98 27 67 91 99 Paraquat 0.18 Oil 1 qt/A — — — 73 Oil 2 qt/A 63 43 43 - Ag 98 — — — 53 Paraquat 0.25 Oil 1 qt/A 63 56 23 72 Oil 2 qt/A 70 43 16 — Ag 98 73 80 33 88 LSD 0.05 8 Percent pigweed control 35 days after treatment Glyphosate 0.19 Oil 1 qt/A 0 95 99 91 Oil 2 qt/A 0 96 96 — Ag 98 13 98 98 95 Glyphosate 0.25 Oil 1 qt/A 23 63 99 98 Oil 2 qt/A 36 67 99 — Ag 98 36 85 99 85 >1 Paraquat 0.18 Oil1 qt/A ._ _ _ 73 Oil 2 qt/A O 0 0 — Ag 98 — — — 0 Paraquat 0.25 Oil 1 qt/A 0 O 0 86 Oil 2 qt/A O 0 0 — Ag 98 0 0 0 43 LSD 0.05 6 aPigweed 2 to 4 inches at treatment on 6/22/83. Plant vigor was poor because the soil moisture level was approaching wilting point. bCotton oil 93 and 7 percent emulsifier. cOne percent by volume of carrier of Ag 98 used on 1.2 and 0.55 gpa, and 0.5 percent used with 26 and 7 gpa. Also, an extra 7 percentX-77 K by volume of carrier was added to the oil to make a sprayable emulsion on the 1.2 and 0.55 gpa carrier rates of carrier. i 4 \_/', in 7 gpa of carrier gave the highest control, and glyphosate at 0.5 lb/A gave 93 percent control of wheat Table 4. Effect of pigweed stage of development on herbicides activity when applied in a carrier volume othat was jointed. When herbicides were applied with a of 26 gpa CDA at 3 gpa, small droplets apparently did not _ penetrate the foliage and there was no control of the Pet's?" p'gweiwd °°"t'°' Wheati“ ‘he hinting Stage S.i;°;°.l2€i.v. “°£2i2“’° 2 T... §°§ $3.11 Z1111. Volunteer Barley Barley with good or excellent plant vigor was _ (lb/A) sprayed with paraquat and glyphosate in carrier B'°m°XY"" 3'32 13g S; g3 volumes of 3 0r 26 gpa (Table 9). This crop was easiest 0:50 100 99 80 to kill if sprayed before tillering. Using 3 gpa of spray Paraquat + 025% wK 0,12 99 95 23 carrier, 0.25 lb/A of paraquat eliminated barley at the 4 Sulfosate + 0.25% WK 0.12 98 94 7 to 5 leaf stage. It took 0.25 lb/A of glyphosate to kill ggglzgsar? iodzgl/g/ol/‘YVKK 1; barley with 4 to 5 leaves sprayed w1th either 26 or 3 gpa Fomesaeenp 0:12 92 90 2o of carrier. Control was about the same or better after 025 92 97 28 the barley had tillered and little control was achieved 0.38 98 91 35 once barley had jointed. No control of jointing barley DlCamba 0-05 58 26 0 was obtained with either paraquat or glyphosate ap- 2g g plied with a CDA at 3 gpa. _________________________________________________________________ __ LSD 0.05 12 12 15 Volunteer Sorghum _ Cohool of sorghum that woo 4 ihohoo on with -?.'?.".‘.Y'.%?.' ....................... -.?T?f’."f'.‘f---?.‘3‘3f’ .... --f’.°.‘ii-- paraquat was better at 3 gpa carrier than with 26 gpa Treatment date 94-83 9-12-33 9-19-83 (Table 10). Glyphosate at 0.25 lb/A gave 95 percent or more control with either 3 or 26 gpa carrier. 9'21'33 9'21"” 947-33 Evaluation date Table 5. Control of pigweed and barnyardgrass with herbicides applied in a carrier volume of 7 gpa Herbicide PGFCGT“ COntTOl Herbicide plus additive rate Pigweed Barnyardgrass (lb/A) Fluazifop + COC 0.18 0 0 Fluazifop + 2,4-D + COCa 0.18 + 1 98 23 Sethoxydim 0.18 13 32 Sethoxydim + 2,4-D + COC 0.18 + 1 91 80 Haloxyfop + COC 0.18 22 3 Haloxyfop + 2,4-D + COC 0.18 + 1 93 12 Quizalofop + COC 0.18 20 83 Quizalofop + 2,4-D + COC 0.18 + 1 67 58 Sulfosate + Ag 98 0.18 97 80 Sulfosate + 2,4-D + Ag 98 0.18 + 1 97 80 Glyphosate + Ag 98 0.18 94 88 Glyphosate + 2.4-D + Ag 98 0.18 + 1 97 85 Glyphosate + 2,4-D + Ag 98 0.25 + 1 90 91 Paraquat + Ag 98 0.18 78 38 Paraquat + 2,4-D + Ag 98 0.18 + 1 95 30 Paraquat + 2,4-D + Ag 98 0.25 + 1 93 40 Fenoxaprop + Ag 98 0.25 22 43 Fenoxaprop + 2,4-D + Ag 98 0 25 + 1 93 45 LSD 0.05 24 25 Weed height 4 inches 5 inches Plant vngor poor poor Treatment date 6-22-83 6-22-83 Evaluation date aAgridex crop oil concentrate at 1 qt/A. bAg 98 surfactant at 0.5 percent of carrier volume. Table 6. Barnyardgrass» control with several carrier volumes and additivesa Carrier volume (gpa) Herbicide Additive Herbicide rate and rate 26 7 1.2 0.55 \4 (lb/ A) Percent barnyardgrass control 6 days after treatment Glyphosate 0.19 on 1 qt/Ab 11 e7 92 99 Oil 2 t/A 0 67 93 — Ag 98 23 76 97 , 94 Glyphosate 0.25 OiI1 qt/A 6 26 76 93 Oil 2 qt/A 9 43 83 — i‘ Ag 9a 2s 5s a1 9a 8' Paraquat 0.18 Oil 1 qt/A — — — 53 Oil 2 qt/ A 37 33 33 — Ag 98 — — — 63 Paraquat 0.25 Oil 1 qt/A 57 47 36 67 Oil 2 qt/ A 53 23 30 — Ag 98 67 60 43 78 LSD 0.05 8 Percent barnyardgrass control 35 days after treatment Glyphosate 0.19 Oil 1 qt/A 0 67 99 95 Oil 2 qt/A 0 77 96 — Ag 98 6 87 99 97 Glyphosate 0.25 Oil 1 qt/A 0 98 99 95 Oil 2 qt/A 16 99 99 — Ag 98 66 98 99 93 Paraquat 0.18 Oil 1 qt/A — — — 3 Oil 2 qt/ A 0 0 0 — Ag 98 — — — 0 Paraquat 0.25 Oil 1 qt/A 0 0 0 66 Oil 2 qt/ A 0 0 0 — Ag 98 0 0 0 36 LSD 0.05 6 aBarnyardgrass 3 to 6 inches at treatment on 6/22/83. Plant vigor was poor because the soil moisture level was approaching wilting point. bCotton oil 93 and 7 percent emulsifier. COne percent by volume of carrier of Ag 98 used on 1.2 and 0.55 gpa, and 0.5 percent used with 26 and 7 gpa. Also, an extra 1 percent X-77 by volume of carrier was added to the oil to make a sprayable emulsion on the 1.2 and 0.55 gpa carrier rates. Volunteer Corn Two studies were conducted. In each case, corn was 10 inches tall and plant vigor was either fair or good. In one study, carrier volumes of 7 and 26 gpa were compared (Table 11) and in the other, 7 gpa of carrier was used exclusively (Table 12). Where two carrier volumes were compared, best control was from glyphosate at 0.25 lb/A in 7 gpa of spray carrier. Paraquat at 0.25 lb/A did not control the corn. Fluazifop gave 93 percent or more control of corn regardless of carrier_ volume. In the second study, the same trend continued (Table 12). Glyphosate and sulfosate gave 93 percent control of the corn at 0.25 lb/A and paraquat failed. Fluazifop and sethoxydim at 0.25 lb/A gave less con- trol than glyphosate or sulfosate. Discussion The minimum practical amounts of paraquat and glyphosate that controlled different sized plants of pigweed, wheat, and barley are given in Table 13. Two- 6 inch pigweed growing with adequate soil water were killed with 0.20 lb/A of paraquat or glyphosate applied with a CDA at 3 gpa. More herbicide was required if the carrier volume was increased to 26 gpa. Small volunteer winter wheat was killed with 0.18 lb/A of paraquat or glyphosate when applied in a carrier volume of 3 gpa. Winter barley was harder to kill, requiring 0.38 lb/A of paraquat. Glyphosate gave 95 percent or better kill of winter barley. Drought stressed barnyardgrass that was 4 inches tall could not be killed with paraquat (Table 14). - Glyphosate killed barnyardgrass at 0.25 lb/A when“ applied in 7 gpa of spray carrier. Witchgrass was killed when paraquat at 0.25 lb/A was applied in 3 gpa of carrier. Glyphosate at 0.12 lb/A killed Witchgrass in the same carrier volume. Stinkgrass was killed only with 0.25 lb/A glyphosate. Corn and sorghum were both difficult to kill with paraquat, requiring 0.5 lb/A or more to give 93 percent control of 4-inch sorghum. Small corn plants were not killed with paraquat. Glyphosate on the other hand 7 killed both volunteer crops at 0.25 lb/A in 3 to 7 gpa of spray carrier. Table 7. Effect of herbicide and carrier volume on control of witchgrass and stinkgrass Carrier volume (gpa) Herbicide Witchgrass control Stinkgrass control Herbicide rate 3 26 26 26 (lb/A) (percent) Paraquat + 0.5% WK 0.12 — — 36 20 0.25 100 8O 0 45 0.38 100 90 33 48 0.50 — — 53 78 Glyphosate + 0.5% WK 0.12 99 95 23 50 0.25 98 98 95 98 0.38 — — 95 100 0.50 — — 100 100 MSMA 2.0 95 95 95 0 4.0 100 99 98 13 LSD 0.05 7 7 21 21 Stage of grass 12 inch 12 inch 10 inch (mature) (mature) (mature) Plant vigor fair poor poor Application date 7-20-81 7-25-82 7-25-82 Evaluation date 8-6-81 8-25-82 8-25-82 Table 8. Effect of carrier volume and date of herbicide application on control of volunteer wheat Percent wheat control for herbicide application Herbicide Carrier Herbicide rate volume 8-31-78 8-13-82 10-4-82 11-22-82 4-27-83 (lb/A) (gpa) Paraquat + 0.5% X-77 0.19 3 — 95 95 — — 0.25 100 90 99 77 0 0.38 — 98 99 53 O 0.50 100 — — 95 O Glyphosate + 0.5% X-77 0.19 — 82 99 — — 0.25 100 98 — 99 0 0.38 — — 100 99 — 0.50 100 100 — 100 O Paraquat + 0.5% X-77 0.12 7 _ _ - - 13 0.19 — — — — 37 0.25 - 100 — — 57 0.38 — 100 — —— 53 0.50 — 100 — — 77 Glyphosate + 0.5% X-77 0.12 — — — —— 47 0.19 — —- — — —- 0.25 - 100 — — 67 0.38 100 — — 83 0.50 100 — — 93 Paraquat + 0.5% X-77 0.12 26 — — 30 0 0 0 25 52 — 87 85 0 0 38 — — 98 99 28 0.50 93 — 99 100 32 Glyphosate + 0.5% X-77 0.12 — — 43 95 25 0.25 69 — 93 98 53 0.38 — — 98 99 67 0.50 100 — 100 100 83 LSD 0.05 21 5 11 12 6 Wheat state 4 inch 2 inch 5 leaves full tiller jointing Plant vigor good fair good good excellent Evaluation date 9-12-78 8-25-82 5-16-83 5-16-83 6-13-83 Table 9. Effect of carrier volume and date of herbicide application on control of volunteer barley Percent barley control for herbicide application on Herbicide Carrier Herbicide rate rate 10-4-82 11 -22-82 4-27-83 (lb/A) (gpa) Paraquat + 1% X-77 0.25 3 99 27 0 0.38 99 80 0 0.50 100 95 0 Glyphosate + 1% X-77 0.25 53 92 0 0.38 99 93 0 0.50 98 99 0 Paraquat + 0.5% X-77 0.12 26 27 63 7 0.25 80 97 7 0.38 98 99 33 0.50 99 100 30 Glyphosate + 0.5% X-77 0.12 53 67 13 0.25 83 98 43 0.38 100 98 57 0.50 100 99 77 LSD 0.05 13 9 7 Barley stage 4-5 leaves full tiller jointing Plant vigor good good excellent Evaluation date 11-18-82 5-‘1-6-82- 6-13-83 Table 10. Effect of carrier volume on control of volunteer sorghum Percent sorghum control at two carrier volumes Herbicide Herbicide rate 3 26 (lb/A) Paraquat + 0.5% X-77 0.25 80 33 0.50 93 73 1.0 98 90 Glyphosate + 0.5% X-77 0.25 100 95 0.50 100 98 1.0 100 98 LSD 0.05 8 Stage of growth 4 inches Plant vigor good Application date 8-31-78 Evaluation date 9-12-78 The studies indicate a decided advantage of using low carrier volumes with many postemergence her- bicides. There is a big advantage to reducing carrier from 26 to 7 gpa with fan tip spray nozzles. Using CDA applications of 3 gpa or less was very effective against small weeds and volunteer crops. This is in keeping with results of previous researchers who found that reducing the amount of carrier increased phytotoxici- 8 Table 11. Effect of carrier volume on control of volunteer corn Percent corn control at two carrier volumes Herbicide Herbicide plus additive rate 7 gpa 26 gpa (lb/A) Glyphosate + 0.5% X-77 0.06 37 0 0.12 73 27 0.25 97 87 Paraquat + 0.5% X-77 0.06 12 18 0.12 33 12 0.25 28 38 Fluazifop + 0.5% COC 0.2 93 97 LSD 0.05 16 m Corn stage 10 inches Plant vigor fair Treatment date 6-3-82 Evaluation date 6-18-82 ty of glyphosate to annual and perennial weeds (But- ler and Burnside 1983; Green et al. 1982; Jordan 1977; Stahlman and Phillips 1979). Once target plants were large, such as wheat that was jointing, poor control was obtained with a CDA. This is similar to results obtained by Reichard and Triplett (1983) who had‘ h better kill of established forages with fan tips than wit CDA at 6 gpa carrier volume. ~d Table 12. Control of volunteer corn with herbicides Literature Cited applied in carrier volume of 7 gpa Herbicide Corn Buhler, D. G. and O. C. Burnside. 1983. Effect of spray Herbicide rate COHIFOI components on glyphosate toxicity to annual grass. Weed Sci. 31:124-130. (lb/A) (percem) Green, I. ]., E. W. Chenault, D. E. Lavake, and A. F. Wiese. Gwphosate + 05% X47 1982. Weed control with a controlled drOPlet flPplicator. ' Texas A i. Ex . Sta. PR-4025. 8 . Iordan, T. 1977). Effects of diluentIz/Idlumes and surfactant O50 87 on phytotoxicity of glyphosate to bermuda grass. Weed Para uat+ O.5°/0X-77 0.12 25 Sci. 29:79-83. q 0.25 23 Mathers, A. C., H. R. Gardner, F. B. Lotspeich, H. M. Taylor, 0-33 27 G. R. Loose, and R. E. Daniell. 1963. Some morphological, 0-50 32 physical, chemical, and minerological properties of seven Sulmsale + 025% X'77 Southern Great Plains soils. U.S. Dept. Agr. ARS 41-85. 1.0 93 PP‘ 7 and 10' . . Fluazifop 025 65 Reichard, D. L. and G. B. Trlplett. 1983. Paraquat efficacy as Sethoxydim 025 47 influenced by atomizer type. Weed Sci. 31:779-782. 050 7g Stahlman, P. W. and W. M. Phillips. 1979. Effects of water ----------------------------------------------------------------- -- quality and spray volume on glyphosate phytotoxicity. LSD 0.05 31 Weed Sci. 27:38-41. Wiese, A. F. and D. W. Staniforth. 1973. Weed control in Gmwth $1399 10inch conservation tillage pp. 108-113 in Conservation Tillage """""""""""""""""""""""""""""""""""" " the Proceedings of a National Conference. Soil Conserva- ____________________________________________ __‘-i‘_’f’ff____ tion Society of America, Ankeny, Iowa. Application date 6-2-82 Evaluation date 6-16-82 Table 13. Lowest practical rates of herbicides to give 95 percent control of pigweed, volunteer wheat, and volunteer barley Plant size (inches) and plant vigora Carrier 2 6 10 4 Plant species Herbicide volume good good good poor (gpa) Active ingredient (Ib/ A) Pigweed 2,4-D 26 0.50 0.75 1.00 1.00 Paraq uat 26 0.25 0.50 1.00 noneb 3 0.20 0.38 0.50 none Glyphosate 26 0.25 0.50 1.00 none 1 -° - 0.25 3 0.20 0.38 1.00 0.25 1 — — — 0.20 Bromoxynil 26 0.38 none —— — ' Volunteer wheat Paraquat 26 0.38 0.38 none -— 7 0.25 - none — 3 0.20 0.25 none — Glysophosate 26 0.25 0.12 none — 7 0.25 — 0.50 — _ 3 0.20 0.25 none — Volunteer barley '_ Paraquat 26 0.38 0.25 none — 3 0.25 0.50 none — Glysophosate 26 0.38 0.25 none — 3 0.38 0.38 none — 1' aVigor ratings were: poor, fair, good, and excellent. bNone indicated that no herbicide rates evaluated gave 95 percent control of pigweed or volunteer crop. cNo tests were conducted on the indicated plant species. Table 14. Lowest practical rates of paraqlfiatrfor glyphqsate to give 95 percent control of several weeds and volunteer‘ " \ ~ k \ »-//,,z,2/5 \*~ '//’ /» ' / Plant size (inches) and plant vigora L; Barnyardgrass ‘Witchgrass Stinkgrass Sorghum Corn Spray 4 4 4 6 10 carrier poor if _ _ v poor poor poor good (gpa) Active ingredient (lb/ A) Paraquat 26 ~'~~ v _, noneb - __ none none none none 7 ' —° _ fi —- - none v 3 none 0.25 —— 0.5 none Glyphosate 26 ’ none 0.25 0.25 0.25 none 7 0.25 — — — 0.25 3 —— 0.12 — 0.25 0.25 aVigor ratings were: poor, fair, good, and excellent. bNone idicates that no herbicide rates evaluated gave 95 percent control of the weeds or volunteer crop. °No tests were conducted on the indicated sized weed or volunteer crop. Appendix. Description of herbicides used in this text Common or chemical name Manufacturer Trade name Formulation Alkylaryl polyoxyethylene 100% Chevron Chemical Co. X-77 90% glycols free fatty acids and isopropanol Alkylaryl polyethlene glycols Flohm & Haas Co. Ag 98 80% Bromoxynil Rhone-Poulenc, Inc. Buctril 2 lb/gal Fenoxaprop American Hoechst Whip 1.67 lb/gal Fluazifop lCl Americas, Inc. Fusilade 4 lb/gal Fomesafen lCl Americas, Inc. Reflex 2 Ib/ gal Glyphosate Monsanto Roundup 3 lb/gal MSMA Diamond Shamrock Corp. Bueno 6 lb/ gal Paraquat Chevron Chemical Co. Paraquat 2 lb/ gal Paraquat lCl Americas, Inc. Gramoxone 2 lb/gal Quizalofop DuPont Co. Assure 0.8 lb/ gal Sethoxydim BASF Poast 1.5 lb/gal Haloxyfop Dow Chemical Co. Verdict 4 lb/ gal Sulfosate Stauffer Chemical Co. Touchdown 2.8 lb/ gal Trimethylnonyl DuPont Co. WK Surfactant 90% polyethoxyethanol 2,4-D Several 2,4-D 4 lb/gal U 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. All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, color, religior sex, age, handicap, or national origin. 2M—5-87 Q