Thrips has been the topic all week in peanuts and cotton. When I got home Wednesday, thrips were all over the inside wheel well of the truck after being in peanuts that afternoon. I talked with Dr. Abney about foliar insecticide sprays on peanuts, and while there is no definitive answer to the question of when should we pull the trigger on a foliar insecticide treatment for thrips in peanut, UGA Extension Peanut Entomologist Dr. Mark Abney just put out these thoughts to consider:
Peanuts with No At-Plant Insecticide
If you are seeing a lot of adult thrips on seedling peanut AND no at plant insecticide was used, it is time to spray. We could spend lots of time debating about the perfect timing, and in theory it would be best to wait until you see immature stages before making a treatment… In the real world in 2016, there are probably immature thrips in the field already, and waiting to treat will just increase the amount of damage you are going to see next week. If we wait until after the terminals have turned brown to spray, we have not done ourselves any favors.
Peanuts with At-Plant Insecticide
The decision to over spray a field that was treated with an at-plant insecticide is not so easy. We almost always see some adult thrips in our plots regardless of the treatment; this is especially true while the thrips flight is active (as it has been for a couple weeks). So, how do we know if those adults are going to die or survive and make more thrips? We do not know for certain, and that is why it is difficult to make a management decision.
I rated my earliest planted thrips trial on Tuesday of this week (planted 29 April). Damage ratings in the untreated plots were similar to what I have seen in previous years during moderate to heavy thrips flights. With the number of adults and immature thrips I saw on Tuesday, I would expect damage to progress rapidly over the next seven days. In the (above)picture of untreated peanut seedlings, the terminals appear green and relatively healthy. Next week’s picture will probably tell a different story.
The good news is that we are finally getting some rain. Fields treated with Thimet are showing thimet burn following rain, which is a physiological response to the chemical in the plant. I was also seeing some leaf tip burn of terminals were thrips were feeding. They of course have to feed on the leaves before dying. Dr. Abney said our at-plant insecticide fields and no insecticide fields actually look the same this week. However, in a week’s time, our no insecticide fields will look hammered – since the thrips are feeding AND reproducing down in the terminal. At-plant insecticide fields will hold out much longer with only adults feeding.