Late-Season Rootworm Control Peanut Notes No. 103 2018

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Controlling Southern Corn Rootworm Late in the Season

Rick Brandenburg

Department of Entomology and Plant Pathology

This time of year it is not uncommon for the question about the cost effectiveness of treating for rootworms to come up in peanuts. After all June was hot and dry and it did not appear like it was going to be a good year for the moisture-loving rootworms, Then the weather flipped on us in July and with cooler temperatures and plenty of rain in most places. As that trend continues, farmers began to think about whether treating for rootworms might not be a bad idea. So the rains continued and there are rootworms out there and there is some pod damage. Lorsban is our only real option and it is very water insoluble and slow to get down into the soil and get to work. It can also aggravate spiders mites in a big way.

So what should a grower do this week of August 5-11? Well we are really close to the end of the line for the Lorban providing much benefit, but there are a lot of beetles laying eggs and the forecast is for some rain to continue to fall over the next 10 days. Spider mites are not a concern right now. Lorsban will give you some decent control of caterpillars in the crop just due to the vapor action. If Lorsban is put out this week and gets some good rains on it within the next few days, it can provide some benefit and still reduce some additional rootworm damage. Should it not rain for 10 days after you put it out, then you won’t get much if any rootworm control, it will still kill some caterpillars, and if it doesn’t rain for 3 weeks, you might stir up spider mites. If your fields were planted late this year, then there is a greater likelihood you will get a benefit simple because the smaller pods usually are hit the hardest.

Something that needs to be understood is that there is already some rootworm damage out there. A farmer might treat and then not be happy when he digs as he will think the Lorsban did not work well. Could be old damage. Second item is that even with good rains, Lorsban takes awhile to get the rootworms. Certainly isn’t going to happen in 48 hours

So when is the real cutoff date? Not sure of that one, but late August is probably a real waste of money.