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DIFENZOQUAT (AVENGE)
A NEW HERBICIDE
FOR WILD OAT CONTROL
S.D. Miller, John D. Nalewaja and C.E.G. Mulder
ABSTRACT
Wild oat causes yield losses and additional production costs estimated at over S150 million per year in North Dakota. Difenzoquat (Avenge) is a new postemergence herbicide for wild oat control in barley, winter wheat. durum wheat, and several spring wheat varieties. Certain wheat varieties have been nearly as susceptible to difenzoquat as wild oat, so use only for wheat varieties listed on the label.
Introduction
Wild oat (Avena fatua L.) continues to be the most troublesome annual weed in small grains in North Dakota. A survey conducted in 1973 (5) indicated 57 percent of the small grain acreage in the state was moderately to heavily infested with wild oat.
Wild oat can be controlled effectively in small grains by preemergence applications' of triallate (Far-go) or postemergence applications of barban (Carbyne); however, farmer acceptance of these herbicides has not been extensive. Triallate requires applications before the wild oat is visible and barb an is only effective on wild oat in the 1- to 2-leaf stage (4). Further, applica tion of barban is not always possible during the limited period of wild oat susceptibility because of adverse weather. Difenzoquat (Avenge) has shown promise as a selective postemergence herbicide for wild oat control at the 3- to 5-leaf stage (3,7). Difenzoquat would thus allow control of larger wild oat than barban and would allow control over a longer time. Experiments were conducted at several locations throughout the state to evaluate difenzoquat for wild oat control in barley and wheat.
Materials and Methods
Wild oat control in barley and wheat. Six experi-
Dr. Miller is assistant professor. Dr. Nalewaja is professor. and Dr. Mulder is research associate, Department of Agronomy. Cooperative investigation by the ND Agric.
Exp. Stn .. and The Agric. Res. Ser.. u.s. Dept. of Agric.
ments were conducted at experiment stations through out North Dakota in 1975 and 1976 on land moderately to heavily infested with wild oat (40 to 90 plants per square yard). Beacon barley was seeded May 10 and 31 at Minot and Langdon in 1975, April 13 and May 11 at Fargo and Minot in 1976, and Hector barley May 20 and 27 at Williston in 1975 and 1976; respectively. Olaf wheat was seeded May 16 and 31 at Williston and Langdon in 1975, April 13 and 27 at Fargo and Williston in 1976, and Ellar wheat May 10 and April 13 at Minot in 1975 and 1976; respectively.
Barban was applied with a bicycle wheel plot sprayer at the 1.5- to 2-leaf stage of wild oats and difenzoquat at the 3.5- and 5-leaf stage. The crops generally had 0.5 to 1 more leaves than the wild oat when treatments were applied. Treatments were applied in 8.5 gallons per acre (gpa) water at a pres sure of 40 pounds per square inch (psi) except barban which was applied in 4.7 gpa water at 45 psi in 1976. Visual ratings for wild oat control and crop injury were made after the crop and wild oat had headed. DiJenzoquat in combination with several herbicides for broadleaf weed control. Beacon barley was seeded at Fargo in a silty clay soil April 13 in 1976. Herbicide treatments were applied to wild oat in the 4.5- to 5-leaf and barley in the 6-leaf stage. Difenzoquat-broadleaf herbicide combinations were applied as a tank-mix in 8.5 gpa water at 40 psi. Visual weed control ratings were made after the wild oat and barley had headed.
Wheat variety response. Hard red spring and durum wheat variety susceptibility to difenzoquat was evaluated at Fargo in silty clay soil from 1974 to 1976. Seeding dates ranged from April 15 to June 1 depending upon the year. Treatments were applied in
8.5 gpa water at 40 psi when the plants were in the 4 to 5-leaf stage. Visual ratings were made three to five weeks after treatment.
Results
'Wild oat control in barley and wheat. Wild oat control was 17 and 19 percent better with difenzoquat at 12 and 16 oziA than with barban in barley ~Table 1). Difenzoquat at 12 and 16 oz/A gave similar wild oat control of 86 and 88 percent, respectively. Further, barley was very tolerant of the rates of difenzoquat and barban applied. Barley yields were increased 5. and 4.9 buiA by 12 and 16 oz/A of Difenzoquat or 5. bul A by barban when compared to the untreated control plots. The better wild oat control with difenzoquat compared to barban was not reflected in a higher yield because of the earlier removal of wild oat with barban.
Wild oat control was 14 and 18 percent better at the 3.5·1eaf stage or 27 and 31 percent better at the 5-leaf stage with difenzoquat at 12 and 16 oz/A than with barban in wheat ~Table 2). Wild oat control was similar with both difenzoquat rates regardless of stage at ap plication. However, difenzoquat application at the 5 leaf stage of wild oat was 13 percent more effective than at the 3.5-leaf stage. Difenzoquat at 16 oz/A ap plied at both stages of growth caused wheat injury rated visually at 6 to 10 percent. However, recovery from injury was good as no symptoms other than a two to three day delay in maturity were observed. Wheat yields were increased 5.0 and 5.9 bul A at the 3.5-leaf stage or 4.8 and 4.6 bu/A at the 5-leaf stage by difenzoquat at 12 and 16 oz/A or 5.5 buiA by barban when compared to the untreated control plots. Again, the better wild oat control with difenzoquat at both stages compared to barban was not reflected in a higher yield.
Difenzoquat gave 11 percent better wild oat control at the 3.5-leaf stage of wild oat in barley than wheat when averaged over 12 and 16 oz/A ~Table 1,2). The better wild oat control in barley was probably because barley competes with wild oat better than wheat. Crop competitiveness has been reported to influence wild oat control with difenzoquat ~3). Difenzoquat was not applied at the 5-leaf stage in barley; however, wild oat control probably would have been increased similarly to the increase observed in wheat.
Difenzoquat in combination with several herbicides for broadleaf l1'eed control. The addition of 2, 4-D DMA ~dimethylamine) or LVE (low volatile ester), MCPA DMA, or bromoxynil plus MCPA ester had no effect on wild oat control with difenzoquat (Table 3). Wild oat control with the various treatments ranged from 90 to 92 percent. O'Sullivan et al. ~6) have re ported that ester formulations of 2,4-D tended to en hance the effectiveness of difenzoquat on wild oat in Canada. However, this study indicated no enhance ment or loss of wild oat control from the addition of either 2,4-D ester or amine to difenzoquat. Difenzo
quat did not reduce common lambs quarters control with any of the broadleaf herbicides. Barley yields were increased 4.4 to 4.8 bul A by difenzoquat in com bination with the broadleaf herbicides when compared to the untreated control plot.
Wheat variety response. Hard red spring wheat varieties were generally more susceptible to injury with difenzoquat than durum wheat varieties ~Table 4). Durum varieties were all similarly injured at about 19 percent with 16 oz/A difenzoquat; whereas, spring wheat variety injury ranged from 23 to 62 percent. Spring wheat varieties Waldron and Tioga were the most susceptible to difenzoquat. Susceptibility of Era and Kitt to difenzoquat was similar to the durums. Further, Era and Kitt tended to be slightly more resistant to difenzoquat than Olaf or Ellar at 16 oz/A and the difference was more pronounced at higher difenzoquat rates (data not shown).
Discussion Difenzoquat provided excellent postemergence wild oat control in barley; however, selectivity in wheat was influenced by cultivar. The use of difenzoquat in a wild oat control program should be limited to barley and tolerant wheat varieties. Waldron and Tioga were the most susceptible wheat varieties to difenzoquat and on occasion were as susceptible as wild oat. Spray ing Waldron and Tioga with difenzoquat is not recom mended. Difenzoquat has given more consistent wild oat control when applied at the 5- and 3-leaf stage of wild oat. However, with heavy wild oat infestations, applications should be at the earliest stage of growth to minimize competitive losses. Further, the highest labeled difenzoquat rate should be used when early applications are made to dense stands of wild oat to maximize control. Time of application could be delayed and the lowest labeled difenzoquat rate used with light wild oat infestations without greatly reducing yield.
Even though difenzoquat did not increase crop yields above those obtained with barban, wild oat seed production should have been reduced more than with barb an because of the better wild oat control. The influence of a treatment on wild oat seed production is important when considering future infestations. Difenzoquat was compatible with MCPA, 2.4-D or bromoxynil plus MCPA which allows the control of both broadleaf weeds and wild oat with one applica tion.
Greenhouse and growth chamber experiments conducted at North Dakota State University have indicated that climatic and soil factors which promote plant growth have generally enhanced wild oat control with difenzoquat. Field observations have confirmed that adequate soil moisture and fertility enhance wild oat control in wheat and barley. These conditions not only enhance difenzoquat activity, but also promote greater crop competition with wild oat.
