Alabama Peanuts: Weather and Insects – Major Shifts in Pest Activity, Abundance

Velvetbean caterpillar moth on peanuts. Photo: Alabama Cooperative Extension

This report is based on continuous insect monitoring information (May to August) using sticky wing pheromone traps. In this article we have also compared insect counts from 2016 (a drought year) and 2017 (a wet year) to provide some interesting trends to readers.

Current pest activity in peanuts:  In recent weeks, caterpillar populations in peanuts have shown a dramatic shift among different pest species. In early August, we reported unusually high cabbage looper and soybean looper activity along with armyworms in the majority of fields scouted (blog post on Aug 11, 2017).

However, this week we observed a dramatic increase in the number of velvetbean caterpillar (VBC, in picture) moths flying inside the peanut foliage. VBC is a highly migratory pest that builds up suddenly and rapidly in peanut fields.

In the large research plots at Headland, VBC moth numbers have suddenly reached 1 moth per foot of row (average); at this population level, moths were flying with every step taken in the peanut plots. This high moth activity will eventually result in an outbreak of VBC caterpillars that will graze the peanut foliage in coming days.

Together with loopers and armyworms, we expect VBC to raise the caterpillar numbers to over 4 per foot of row that may trigger some insecticide applications. Therefore, we recommend commercial peanut producers to immediately scout their peanut fields and note the caterpillar numbers/species diversity before initiating insecticide treatments. Insecticide efficacy depends on the pest species, so pest identification is critical.

Please refer to the earlier blog post regarding caterpillar treatment recommendations and use a combination of chemicals to prevent spider mite outbreaks.

comparison chart 9-2-17.jpg

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Comparison of 2016 and 2017 production years:  In the table alongside we have compared pheromone trap catches across the two years. It is clear that many moth species like the dry weather; the difference in armyworm, looper, and lesser cornstalk borer numbers show the strongest trends.

Data comparison also indicates that in a wet year like 2017, peak insect activity can shift 2 to 3 weeks into the growing season due to a variety of factors. Fluctuating temperatures and high natural enemy numbers could be some of the factors that delayed moth/caterpillar activity this year.

The good thing is that peanut plants grow fast and compensate for insect feeding in wet years, although early onset of diseases can be devastating to the crop. The whole point is that every production year is different and IPM plans have to suit the weather fluctuations.

For more help with IPM plan for peanut insect pests, please call an agronomic crops regional extension agent, the authors, or go online for downloading the 2017 Peanut IPM Guide.

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