The 2023 growing season has brought a range of stress inducing weather patterns, from drought to waterlogging. Stressful conditions can make crop plants more susceptible to injury from postemergence herbicides. Below are some examples of injury we have seen so far this year.
Yellow flash (glyphosate)
Temporary yellowing of newly emerged soybean leaves due to glyphosate application to glyphosate-resistant beans. More common in:
- Conditions conducive to rapid soybean growth (high temperatures and/or humidity)
- High rates/areas of overlap
- Areas with micronutrient deficiency
Injury often appears one to two weeks after application and often disappears by 21 days after the area was treated. There is no evidence of yield loss from this phenomenon.
Injury symptoms where glufosinate was applied to glufosinate-resistant beans:
- Chlorosis, or yellowing, and some necrosis
- Often worse when applied in hot, humid conditions
- Injury often short-lived
Group 15 herbicides are an important component of late-season waterhemp management in soybean. Use of herbicides like Warrant are known to cause some leaf malformation, which in some instances can look similar to the leaf injury from group 4 herbicides. Some important differences are:
- Group 15 injury: heart shaped leaves, shortened midveins, leaf crinkling, irregular symptomology
- Group 4 injury: leaf cupping or strapping, parallel leaf venation, symmetrical symptomology
PPO inhibitors like Flexstar are known to cause some injury when applied postemergence.
- Leaf speckling or bronzing
- Injury often worse when applied in hot humid conditions
- Plants typically overcome injury within 30 days with no yield loss
Ohio typically receives enough rainfall that carryover is not likely if labeled rotational intervals are followed. The droughty conditions this past fall and early spring are causing some concerns over carryover of corn herbicides to soybean and vice versa. Environmental conditions and nutrient deficiencies can cause similar looking issues. Some considerations for diagnosing carryover include applications made the previous season and the herbicides used, injury symptomology, soil type and pH, and environmental conditions.
Lots of great resources exist with pictures of the abovementioned injury symptoms associated with different herbicide groups used postemergence:
Yellow Flash in Soybean
Tips for Identifying Postemergence Herbicide Injury Symptoms in Soybean
Herbicide Injury Symptoms on Corn and Soybeans
Identifying Common Herbicide Symptoms in Soybean
Quick Guide to Herbicide Injury on Soybean
Herbicide Injury to Corn