By Dwight Lingenfelter and John Wallace
Over the past few weeks we have received calls asking for burndown herbicide suggestions for fields that are adjacent to sensitive crops such as vineyards or specialty crops. Most broadleaf plants (e.g., grapes, vegetables, fruit crops, ornamentals, certain trees, non-tolerant soybeans, tobacco, etc.) are extremely sensitive to plant growth regulator (PGR) herbicides. PGR herbicides include phenoxy, benzoic and pyridine classes of compounds. The most common PGR herbicides used are those containing 2, 4–D or dicamba. But others, which have been documented as causing injury include: picloram (e.g., Tordon), triclopyr (e.g., Garlon), and clopyralid (e.g. Stinger). All of the PGR herbicides should be considered to have the potential to cause injury to non-target sensitive plants as a result of spray drift.
Historically, many of the standard burndown herbicide programs have included 2,4-D, primarily to control glyphosate-resistant marestail and other weeds such as dandelion and winter annuals. And with the advent of Xtend soybean varieties, dicamba-products are being used more in burndown programs. However, if crop production fields are near sensitive crops or areas, both herbicides have the potential to cause problems even early in the season if grapes or sensitive trees are starting to bud or break dormancy. In addition, glyphosate drift can cause problems in these settings plus glyphosate-resistant weed species will not be controlled. In cases like this some alternative herbicides for burndown include paraquat (e.g., Gramoxone), glufosinate (e.g., Liberty 280), and saflufenacil (e.g., Sharpen). To improve effectiveness of these products, especially during early spring conditions, make sure to use higher rates, include necessary adjuvants, use higher spray volumes (≥15 gpa), spray when weeds are small (3-5” tall) and actively growing; and apply during sunny days and warm temperatures (>50F daytime). Most of the soil applied residual herbicides that are tank-mixed with burndown herbicides are not volatile and usually don’t cause problems to sensitive crops (unless severe drift occurs). However, no matter what herbicide is being applied it is best to keep the spray in the target area by using low-drift nozzles, spraying in low wind conditions and applying when the wind directions is away from the sensitive area.
A recent article from Dr. Kevin Bradley and his colleagues at the University of Missouri noted that even when using PGR herbicides during the early spring, some reports of dicamba drift occurred to specialty crops and trees. Refer to article for more details: "
Five Things We've Learned about Dicamba."