Spider mites have been reported on a number of crops including vegetables and cotton since this spring, and as conditions continue to be hot and dry in many locations, we are beginning to see populations jump in peanut.
The two spotted spider mite is a challenging pest to control. It thrives in hot, dry conditions where it completes development in as little as seven days at 81 F. Female mites can lay up to 100 eggs over several weeks, so it is easy to see how infestations can go from light to heavy in a very short period of time.
In the early stages of infestations mites will be found mostly on the undersides of leaves. Their position on the plant and the webbing they create make getting good contact with a miticide difficult. Once infestations progress, mites will be seen on lower and upper portions of the leaves. It is very common to see “hotspots” in peanut fields when infestations are just getting started. Mites will radiate out from these areas to infest the rest of the field. Populations often get established along field borders and especially borders adjacent to dirt roads or field paths.
Georgia growers are strongly urged to scout fields for spider mites as early detection can improve the odds of effective control. The ovicidal activity of miticides labeled for use in peanut is limited, so more than one application may be needed to clean up infestations. Propargite (e.g. Comite) is currently the only real option for mite control in peanut. I do not recommend the use of a pyrethroid for two spotted spider mite in peanut.
Fields where granular chlorpyrifos (e.g. Lorsban) was applied for lesser cornstalk borers are at elevated risk for mite infestations. The use of other broad spectrum insecticides like acephate or a pyrethroid may also flare mite populations.
Foliage feeders coming on strong
We currently have a diverse mix of foliage feeding caterpillars in GA peanut fields. Right now, the heliothines (tobacco budworm and corn earworm) are most common, but beet armyworm, fall armyworm, soybean looper, cutworms, and even some velvet bean caterpillars have been reported. Several species are commonly found in the same field. Fields where granular chlorpyrifos (e.g. Lorsban 15G) was applied should be monitored closely for foliage feeders.
Thresholds for foliage feeders remain 4 to 8 caterpillars per row foot. It seems a lot of folks start to get nervous when we get close to 4 larvae per foot. Peanut can tolerate a significant amount of defoliation with no impact on yield, but when we start to see ragged leaves, it becomes difficult to hold back. We do not want to be spraying peanuts just because everyone else is if there are only one or two larvae per foot of row.
Bloom feeding has been observed in peanut for a number of years, and current thresholds do not take this type of damage into account. Peanut produces a lot of blooms, and not all of them will result in harvestable pods even in perfect conditions. The impact of caterpillar feeding on blooms is not known. I think it is reasonable to be more aggressive in making treatment decisions when significant bloom feeding is observed.
What is “significant bloom feeding”? That is a question that will have to be answered on a case by case basis taking into account the condition of the field, number of caterpillars, maturity of the crop, and personal experience.
Fortunately we have some very good options for caterpillar control that will not completely eliminate beneficial insects.