Symptoms

Acetolactate synthase (ALS)-inhibiting herbicides (HG 2) cease the production of branched-chain amino acids, precursors to essential plant enzymes and structures. ALS-inhibiting herbicides can be applied pre- and postemergence. While there are many ALS-inhibiting herbicides labeled for soybeans, injury can still be prevalent. Injury symptomology includes plant stunting, root stunting (i.e. bottle brushing), chlorosis, and purpling of leaf veins. Initial injury can be mistaken for nutrient deficiency; development of ALS-inhibiting herbicide injury on soybeans will be a slow process. The ALS-inhibiting herbicides are phloem mobile which results in injury observed primarily on new plant growth. Injury from the ALS-inhibiting herbicides labeled for soybeans is usually transient, however, ALS-inhibiting herbicides not labeled for soybeans can result in plant death.

Management

Since ALS-inhibiting herbicides can be applied pre- and post-emergence injury can be incurred on emerging and established soybean plants. If soybeans are injured by labeled ALS-inhibiting herbicides, injury will subside over time and no yield loss will occur.

Labeled rotation restrictions should be followed to ensure that soybeans are not injured by carryover of ALS-inhibiting herbicide labeled for other crops and vice versa. Depending on when the previous ALS-inhibiting herbicide was applied, yield losses can range significantly and are often environmentally dependent. Soybeans injured from physical drift from a non-labeled ALS-inhibiting herbicide, incurred injury can vary widely, depending on the dose. Physical drift can be avoided by spraying when the average wind speed is less than 10 miles an hour and mid-day or –afternoon to avoid a temperature inversion.