There have been a lot of phone calls in the past few days with folks concerned about POST applied herbicide tankmix burn on cotton and soybeans. We see burn from POST applied tankmixtures every spring but the crop response from applications over the past 10 days has been more pronounced. I think the two main reasons for the extra burn has been the cool nights coupled with everyone getting used to new POST tankmixtues on Xtend crops.
I really think the weather, particularly the cool nights, has left our soybeans and most certainly our cotton more susceptible to surfactant type burn. The cool and mostly damp conditions have left leaf cuticles thin which makes them more susceptible to burn from POST applied tankmixes. Moreover, the frequent showers have the soil damp which always ramps up POST applied surfactant type burn by 50%.
Most everyone seems to have thought that tank mixtures of Roundup Powermax and either Xtendimax or Engenia would not cause burn. That is incorrect. In our research we are typically see 5 to 10% burn with those tankmixtures in soybean and 20 to 25% burn in cotton.
If anything else is added into the tank like some of the drift reduction agents, surfactants and certainly Warrant, Outlook or Dual Magnum then burn to soybeans is in the 20% range and cotton is showing 30 to 40% burn injury. That is why our standard recommendation is to not to use those 3 way tankmixtures on Xtend cotton. Split them up, ideally with Roundup going last to take out grasses.
Also, any tankmixtures of Liberty with Dual Magnum, Outlook and Warrant has shown more injury this year in soybean and cotton then what I can recall in recent years. In addition, we have seen more burn on soybeans with Liberty tankmixtures with either Prefix or Anthem Maxx then in past years. Again I think the weather is the main reason. On the plus side Liberty is working better on Palmer amaranth right now than I can recall in the past.
Though these crops look rough now, my field experience as well as research has consistently shown that there is typically no impact on yield. Recent cotton research on potential POST tankmixtures in Xtend cotton from Darrin Dodds and Chase Samples at Mississippi State would also suggest that visual injury <35% does not typically reduce yield.