Mark Lawson is a technical service rep for Syngenta. That may make you wonder about his advice not to shave herbicide rates this spring, except other specialists are also saying the same thing. And Lawson has been farming for several decades, plus working off-the-farm.
With more people going back to programs that include residual herbicides to help control resistant weeds, price of weed control is going up. The natural reaction might be to shave rates and save some bucks that way, he says.
Cool springs usually mean weeds are harder to control anyway, since they are more susceptible when they're actively growing, he says. When temperatures are higher, plants are moving material up and down the stem more completely. That's important for systemic products.
"We've also got resistant waterhemp and resistant Palmer amaranth in some areas," he says. Palmer amaranth has now been identified in nearly one-fourth of all Indiana counties. Waterhemp is in at least a third of Indiana counties, and is generally spread in a different pattern across the state than Palmer amaranth.
"The last thing you want to do if you suspect you have either of these species is cut rates," Lawson insists. "These are tough weeds to control as it is."
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In fact if they get above four to six inches postemergence in soybeans, there is no way to bring them down, he says, That's why residual herbicides applied correctly are so important. Palmer amaranth is so bad in some southern states that growers resorted to handweeding, an expensive practice, to try to bringing it back under control.
Cutting rates also can speed up herbicide resistance. If weeds already need higher rates to control than in the past, it's cool and you apply a marginal rate, they're more likely to survive. Those would be the ones that could produce seeds for the future, The net result would be more resistant weeds.