New MSU recommendations for use of 2,4-D formulations in winter wheat
Three years of research are resulting in new recommendations
Historically, it has been thought that applications of 2,4-D amine were “safer” on winter wheat than applications of 2,4-D ester. For several years, MSU recommended reducing the rate of 2,4-D ester to 0.75 pint per acre (pt/A) to avoid these concerns. Over the last three years we have conducted research funded by Michigan Crop Improvement Association to determine if there were differences in crop tolerance and weed control between applications of 2,4-D amine and 2,4-D ester when each were applied at 1 pt/A.
Over the three years of this research, there were no differences in winter wheat tolerance between 1 pt/A of 2,4-D amine and 2,4-D ester when applied to wheat at Feeke’s stages 4 to 5 (prior to jointing). In fact, there did not appear to be any injury from applications of either of the 2,4-D formulations when compared to the non-treated control. Averaged over the three years there was also no significant difference in wheat yield between applications of 2,4-D amine (99.6 bu/A) and 2,4-D ester (100.6 bu/A). Applications of the 2,4-D formulations also helped protect yield from weed competition since wheat yield in the non-treated control was at least 5 bu/A lower than plots treated with either of the 2,4-D formulations.
Weed control was also not different between the two 2,4-D formulations at 1 pt/A. Both formulations provided excellent control of the winter annuals, field pennycress and bushy wallflower, and good control of mayweed chamomile. Generally, 2,4-D is not a strong herbicide for control of common chickweed, as this was also reflected in our research with only about 50 percent control. Control of common ragweed was slightly different between years. However, it was generally fair to good within two weeks of application (WAT). After wheat harvest, plots that had been treated with either 2,4-D formulation were generally clean.
MSU recommends applying either 2,4-D amine or 2,4-D ester at 1 pt/A in the spring to actively growing wheat following tillering (Feeke’s stage 3) but prior to jointing (Feeke’s stage 6). Risks associated with plant growth regulator herbicides, like kernel abortion and blank wheat heads, increase once wheat is at jointing (Feeke’s stage 6) or later. Tank-mixtures with other herbicides, fungicides or adjuvants increase the risk of crop injury. Do not apply 2,4-D in the “boot” (Feeke’s stage 9) to “dough” stage of wheat.
For information on 2,4-D applications with nitrogen (28% UAN) consult my article on Nitrogen (28% UAN) as a spray carrier can affect winter wheat sensitivity to herbicides.