| John D. Nalewaja Professor Department of Agronomy North Dakota State University Fargo, ND |
Stephen D. Miller Associate Professor Department of Agronomy North Dakota State University Fargo, ND |
Poast and Fusilade are postemergence herbicides for the control of grassy weeds in broadleaf crops and have been effective and safe in experiments on sugarbeets in Minnesota and Eastern North Dakota. Poast has been field tested since 1979 and Fusilade since 1981. Table 1 and Table 2 give paired comparisons of Poast and Fusilade with other postemergence grass herbicides and with each other for control of wild oat and green and yellow foxtail (pigeongrass). Each paired comparison is an average of several experiments which included the two herbicides at the listed rates.
Comparisons in Table 1 and Table 2 should be made only between the two herbicides in a pair because these two herbicides were used in the same experiments at the listed rates. The % weed control for the same herbicide may differ from one paired comparison to another because different sets of experiments were used to make the comparisons.
Carbyne gave wild oat control superior to Dowpon and Dowpon gave green and yellow foxtail control superior to Carbyne. Hoelon, Poast, and Fusilade gave wild oat and green and yellow foxtail control superior to Carbyne and Dowpon. Fusilade and Poast gave wild oat control superior to Hoelon. Poast gave green and yellow foxtail control superior to Hoelon but Hoelon and Fusilade gave similar green and yellow foxtail control. Fusilade gave wild oat control superior to Poast but Potast gave green and yellow foxtail control superior to Fusilade. All the postemergence herbicides for grass control gave variable levels of control among experiments as indicated by the number of experiments which fell in the various categories of control (Table 1 and Table 2); Fusilade for wild oat control and Poast for green and yellow foxtail control had the highest percentage of experiments in the 95 to100% category.
Obviously the comparisons in Table 1 and Table 2 are only valid at the rates tested. For example, Poast could be made to give wild oat control similar to Fusilade if the rate of Poast was increased while keeping Fusilade the same and Fusilade could be made to give green and yellow foxtail control similar to Poast by increasing the rate of Fusilade. The choice among the postemergence grass herbicides should be based on the cost of achieving the desired level of grass control.
The postemergence broadleaf herbicides, Betanex and Betamix, are used extensively on sugarbeets in Minnesota and Eastern North Dakota. Sugarbeet growers will want to tank mix Poast or Fusilade with Betanex or Betamix after Poast and Fusilade become registered for sugarbeets to achieve broadleaf and grass weed control with a single application. Table 3 and Table 4 give a summary of results of several experiments which compared weed control from Poast or Fusilade alone to Poast or Fusilade in combination with Betanex. The term antagonism used in Table 3 and Table 4, is the reduction in grass control caused by adding Betanex to Poast or Fusilade compared to grass control from Poast or Fusilade alone.
The addition of Betanex to Poast or Fusilade reduced the average control of tame and wild oat compared to Poast or Fusilade alone (Table 3). Control by Poast was reduced more than by Fusilade. The antagonism between Poast and Betanex caused 5% or greater loss in tame and wild oat control in 6 of 8 experiments while the antagonism between Fusilade and Betanex causes 5% or greater 1088 in 4 of 8 ,experiments. Fusilade plus Betanex gave slightly more tame and wild oat control than Fusilade alone in 3 of 8 experiments. The foes in tame and wild oat control from combining Betanex with Poast or Fusilade was not a consistent 1088. However, the loss was frequent enough and severe enough that Poast and Fusilade should be applied separately from Betanex to give optimum tame and wild oat control.
The addition of Betanex to Poast that only a slight effect on the average control of green and yellow foxtail compared to Poast alone but Betanex plus Fusilade gave less foxtail control than Fusilade alone. The antagonism between Betanex and Fusilade caused 5% or greater loss in foxtail control in 6 of 10 experiments. Only 3 of l4 experiments lost from 6 to 10% foxtail control from Betanex plus Poast compared to Poast alone. Thus, Betanex could generally be applied in combination with Poast without a significant loss in green and yellow foxtail control but the tested rates of Fusilade and Betanex should be applied separately for optimum foxtail control.
Broadleaf weed control was not reduced by combining Betanex with Poast or Fusilade (data not presented). Also, Poast and Fusilade must be applied in combination with one of a group of specially formulated oil additives in order to achieve consistently effective grass control. Both petroleum oil and crop origin oil additives have been effective in increasing grass control from Poast and Fusilade. The experiments to date suggest that the petroleum oil additives are slightly more effective than the crop origin oil additives (data not presented).
The required use of an oil additive with Poast and Fusilade will often increase the sugarbeet injury from Betanex if Betanex is tank mixed with Poast or Fusilade (Table 5).
Betanex plus Poast or Fusilade caused less than half as much sugarbeet injury as Betanex plus oil concentrate plus Poast or Fusilade. Betanex did not substitute for the oil concentrate in increasing grass control from Poast or Fusilade as Betanex plus Poast or Fusilade gave less wild oat control than Betanex plus oil concentrate plus Poast or Fusilade. Antagonism is one problem with combinations of Betanex or Betamix with Poast or Fusilade and increased sugarbeet injury from using oil concentrate with Betanex or Betamix is a second problem. Sugarbeets with 2 leaves or less are too small to consistently tolerate Betanex or Betamix plus oil concentrate even with reduced rates of Betanex or Betamix. Sugarbeets should have 4 leaves before oil concentrate is used with Betanex or Betamix. Thus, tank mixes of Betanex or Betamix with the postemergence grass herbicides could be considered a) when target grass weeds are green and yellow foxtail, b) when sugarbeets have 4 leaves or more, and c) not over 0.5 lb/A of Betamix or Betanex should be used unless weather is cool and cloudy or sugarbeets have 6 to 8 leaves.
Research in 1983 indicated that sugarbeet injury was less from Betanex at 0.5 lb/A followed 5 days later by Betanex plus Poast plus oil concentrate at 0.5 + 0.2 lb/A + 1 qt/A as compared to Betanex plus Poast plus oil concentrate at 0.5 + 0.1 lb/A + 1 pt/A applied twice at 5 day intervals (see paper on kochia control in this copy of the Sugarbeet Research and Extension Reports). Poast gives good to excellent control of green and yellow foxtail over a wide range of growth stages so application of Betanex or Betamix plus Poast plus oil concentrate can be delayed until the sugarbeets reach the 4 leaf stage without reducing foxtail control. The stage of growth of broadleaf weeds is much more critical so Betanex or Betamix alone should be applied at reduced rates to small sugarbeets when broadleaf weeds are a problem.
Antagonism can be overcome by increasing the rate of-the grass herbicide (Table 6).
Betanex plus Poast or Fusilade gave-less wild oat control than Poast or Fusilade alone. Betanex plus Poast at l + 0.4 lb/A gave wild oat control similar to Poast at 0.3 lb/A alone. Betanex plus Fusilade at 1 + 0.4 lb/A gave wild oat control similar to Fusilade at 0.2 lb/A alone. Thus, increasing the rate of Poast or Fusilade will overcome the antagonism between Betanex and Poast or Fusilade. Increasing Poast or Fusilade rate could be considered if the advantages of using a tank mix are more important than the increased cost of herbicide.
Antagonism between Betanex and Poast or Fusilade can be avoided by separate applications. The time between applications that is needed to eliminate antagonism was the objective of two experiments conducted at Fargo in 1983 (Table 7).
The tank mix of Betanex and Poast gave l9% less wild oat control than Poast alone. A single day between Betanex and Poast applications reduced but did not eliminate antagonism when Betanex was applied first. Two days between applications gave wild oat control similar to Poast alone. When Poast was applied first, a single day between Poast and Betanex applications eliminated antagonism. These results need to be confirmed by additional field trials but the data suggests that two days between applications would eliminate antagonism regardless of which herbicide was applied first.
1983 Sugarbeet Research and Extension Reports. Volume 14, pages 69-74.
