Soybean Response to Soil Applied Herbicides

Soybean Response to Soil Applied Herbicides
Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

A Delaware Soybean Board funded project looked at relative soybean safety to commonly used soil-applied herbicides. In this trial we included herbicides at 1.5 times the normal use rate for our loamy sand soils.

chlorimuron and metribuzin were not applied alone in this study.

Herbicides were applied alone and in two- and three-way combinations. We include four different soybean varieties that had different levels of sensitivity to metribuzin and PPO-herbicides (sulfentrazone or flumioxazin).

Chlorimuron was the most injurious active ingredient in this study. Injury from chlorimuron developed slower than other active ingredients and soybeans were slow to recover. But visual injury did not translate to yield reductions. Many of the best yielding plots were treated with chlorimuron.

In general, sulfentrazone caused more injury than flumioxazin, ranging from 14 to 17% injury versus 7 to 11% injury at 20 days after planting. As noted in the table above, soybeans injury less from 20 to 33 days after planting. Metribuzin was not as injurious as anticipated, with no injury was more than 10%. Furthermore, metribuzin applied with Dual, Zidua, Prowl H2O or Linex did not increase injury compared to these herbicides applied alone. It should be noted that injury of 10% or less is difficult to detect in the field without an untreated check for comparison. So other than chlorimuron, herbicide injury was not very noticeable (and this was at high rates of the herbicides). Finally, injury was a poor predictor of yield response. There were few yield differences in this trial, and they were not correlated with soybean injury.

This trial had one planting date, but future trials should include planting date as a variable to determine the impact of less-than-ideal growing conditions on soybean injury. Additional work is needed to determine the consistency of these results.