Dicamba | Too Hot to Spray

Farmers and retailers have been under pressure this season to get herbicides applied to soybeans and it has caused a lot of headaches. A Ninth Circuit Court of Appeals ruling caused a five-day pause in the application of three of the four available dicamba products. In Illinois, unlike other states, that pause was upheld and then the state tried to remedy the situation by adding five days to the application window - which now closes June 25th. Mostly it is going to be too hot spray during that time frame. Another regulation prohibits application on days warmer than 85 degrees says University of Illinois Extension Weed Scientist Aaron Hager, “Looking at the long term forecast from the National Weather Service, it looks like the next five days will be a no-spray situation. We’ve high temperatures well in excess of 85 degrees for today, Friday, Saturday, Sunday, and on into Monday. So, of the seven days we have left, it looks like on the extended forecast there may be only about two days.”

Regulations require the forecast to be checked within 24 hours of the intended application says the ILLINOIS Extension Weed Scientist, “The forecast can change over time but it looks like, at least for the next several days, we are going to have to leave the Dicamba sprayers parked.”

That’s for the Dicamba resistant soybeans. Other soybeans just look awful. There have been herbicide products for decades that burn the leaves of soybeans and then they grow out of it but this year’s damage is, well, in a word serve. Again, here’s ILLINOIS’ Aaron Hager, “A couple of possible reasons why that could be the case. 1) The environmental conditions, obviously, when these were applied. If they are applied under very warm air temperatures under bright sunshine we tend to see more soybean response compared with applications that happen under cooler and perhaps cloudy skies.”

The other possible explanation lies in the practice of adding a residual herbicide into the post-application herbicide mix. Hager says some of the residual herbicides could be acting in the tank mix like an additional crop oil. This would lead to a more rapid uptake of the herbicide and a consequently quick and extensive development of the burning leaf symptoms.

Returning to Dicamba soybeans. Illinois farmers unable to make applications by June 25th will need to use alternative products; Glyphosate, PPO inhibitors, or both. The problem is that waterhemp is likely to be resistant to one of the two, and maybe both. If that is the case, Aaron Hager says there are no good chemical options for the field.

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