Few pests of peanut are as dreaded or as difficult to control as the two spotted spider mite. Spider mites generally start to show up in peanut fields in late July, and if conditions are favorable they can severely injure or even kill plants. Hot and dry are the main ingredients in the recipe for spider mite infestations. Applications of broad spectrum insecticides like pyrethroids and organophosphates can flare mite populations and make a difficult situation much worse.
Growers are urged to check fields for signs of mite infestations. We typically see mites appear around field edges especially near dirt roads and field paths. Mowing vegetation along roadsides and field margins can result in migration of mites into peanut fields.
Mite populations can quickly explode this time of year, and waiting a week to see what is going to happen with mites can be a mistake. When we do treat a field for spider mites, water volumes of 20 gallons or more per acre and high spray pressure will improve coverage and control. Comite is still the only true miticide registered for use in peanut, and applications are not cheap. Because Comite does not have good activity on mite eggs, two applications are often needed to get infestations under control especially if large numbers of eggs are present when the first treatment is made. I have never seen any miticide control mite populations effectively once the foliage had turned brown or black and mites were massed under webbing in the terminals of the plants.
At this point in the season, I would be aggressive with mite management decisions in fields that still have good yield potential. Rainfall events can reduce mite numbers, but mites are not going to disappear after one or two afternoon thunderstorms. Growers should also use caution when spraying routine fungicides or other chemicals in peanut fields as mites can be moved very easily from field to field on tractors and other spray equipment.