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Why Isn't My Insecticide Seed Treatment Controlling Black Cutworm?

Why Isn't My Insecticide Seed Treatment Controlling Black Cutworm?
It's all a matter of strength of insecticide vs. number of larvae.

You've been shrugging off all these reports about black cutworm moth catches and the possibility of black cutworms affecting your fields. You ordered your seed coated with one of the seed insecticides. So you figure you're in the clear.

Not so fast. Purdue University entomologists Christian Krupke and John Obermeyer are warning farmers that just because they planted corn treated with a seed-coated insecticide doesn't mean they don't have to scout and pay attention for black cutworm outbreaks.

This is a year of record moth catches. Depending upon weather conditions, that could mean significant egg laying, especially in fields that were covered with vegetation until right before planting. If the pressure is severe, meaning the number of black cutworm larvae are very high, the seed-coated insecticide may not be up to the task of providing total control. The entomologists suggest you can expect suppression, but not a total wipe-out of the insects. Whether suppression is enough to prevent plant cutting to the degree that you should apply a foliar insecticide is what field scouting is all about.

The other question to ask is which product was your seed treated with, and at what rate? Most of the insecticides come in three rates, such as 250, 500 and 1250. The 1250 rate is usually applied if you're after rootworm control. However, even at that rate, research results over the past several years in Illinois and Indiana have shown that rootworm control under heavy pressure won't come close to matching traditional methods of control, such as spoil-applied insecticides for rootworms. And it won't match control by corn with the Bt trait for rootworms, either.

If your seed was treated with one of the lower two rates, then it's even less likely that you could expect total control of black cutworms, unless the infestation in a given field turns out to be very light.

The same may be true of corn with the Bt trait that is supposed to handle black cutworm, they add. Depending upon the trait, it may provide more suppression than actual control if black cutworm pressure is very heavy. Check with your seedsman to see what you can expect.

The entomologists prefer scouting field by field to make sure that black cutworm does not reach economic threshold levels worthy of an additional foliar application of insecticide.

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