By: Mark Abney
We knew they were coming, and now they are here. The calls, emails, and texts have started to roll in reporting peanut fields in Georgia infested with two spotted spider mites. Finding mite infestations early, choosing an effective miticide, and applying the miticide correctly are critically important if we hope to manage this pest. Correct application means increasing spray volume to ensure good coverage of the canopy. The extra time and water it takes to spray right the first time is a lot cheaper than a second or third trip across the field. How much water is enough? Seven gallons is NOT enough, and 20 gallons is better than 15.
Many of the mite infested fields I have seen in 2020 were treated previously with a pyrethroid insecticide. This class of chemistry is known to flare mites in peanut, and we should avoid applying these products to non-irrigated fields when conditions are favorable for mite development (i.e. hot and dry).
Bifenthrin is a pyrethroid insecticide. Even though spider mites are listed on the label, DO NOT APPLY bifenthrin to peanut fields where spider mites are present.
There are two miticides registered for use in peanut (Portal and Comite). Both products can be very effective when applied properly, but even in the best of circumstances treated fields should be monitored closely as a second application may be needed. Spider mite problems tend to occur in fields where yield and quality are already compromised by hot, dry weather. Knowing when to walk away and stop spending money on a crop is difficult. Now is a critical time for insect management in Georgia peanuts. Hot, dry weather is here, and the decisions we make over the next few weeks are going to be very important in determining how much impact insect pests will have on this year’s crop.
Lesser cornstalk borers (LCB) have been in peanut fields for weeks, but populations have increased in areas without rain. We cannot afford to miss or ignore LCB infestations in late July. This does not mean every field needs to be treated; it means we need to scout and treat if the pest is present. Reports of spider mites in cotton are common and have been for several weeks. Spider mites in cotton in June and July is almost always a precursor to spider mites in peanut in August and September. I urge growers to avoid using any pyrethroid insecticides on NON-IRRIGATED peanuts unless it is absolutely necessary. Pyrethroids can, and routinely do, flare mites in peanut. This means I would not treat three-cornered alfalfa hoppers or potato leaf hoppers on non-irrigated acres unless injury was severe.
For growers with three-cornered alfalfa hoppers and leaf hoppers in irrigated fields, I do not generally recommend a special trip across the field, but tank mixing an insecticide with next scheduled fungicide spray is a reasonable choice. Special attention will need to be given to dry corners of irrigated fields especially if they are treated with a pyrethroid. LCB and spider mite infestations can easily be missed if dry corners are not scouted carefully. What looks like drought stress from a distance may actually be insect and/or mite infestations. Regardless of scouting, harvesting dry corners separately from the irrigated portion of the field is a good idea.
A lot of attention is given to foliage feeding caterpillars in Georgia peanuts, and these pests are often sprayed before thresholds are reached. We have very good tools for managing caterpillar pests in peanut, and there is not much reason to make preventive insecticide applications as long as fields are scouted routinely. Selecting the best insecticide for the caterpillar or group of caterpillar species can save growers a lot of money. For example: velvetbean caterpillars can be controlled cheaply, while soybean loopers will be more costly to manage. Preventing economic loss from defoliation and avoiding costly insecticide applications where they are not needed should be our goal. Scouting will be the best defense against losses in 2020. While you might be tired of reading this or hearing me say it, the truth remains: The single most important thing a grower can do to prevent losses due to insects and mites is scout correctly. Once a problem is identified, make an informed decision using the best possible information.