Which Pest to Expect? Some pests like it hot. Some like it cool. Understanding how the environment influences insects will help you anticipate problems this season. Here are four common insects to consider. – DARRELL SMITH

1. Bean Leaf Beetles

Photo: John Obermeyer, Purdue Extension Entomology

Bean leaf beetles show up early and throughout the season, too, depending on the geography and weather. Scott Stewart, University of Tennessee IPM Extension specialist, says he likes to treat beetles based on defoliation levels rather than sheer numbers. He uses a threshold of 20% to 25% defoliation from R1 to R6, relaxes this threshold to 30% to 35% defoliation for the next seven to 10 days after reaching R6 and does not treat after this point. “With this insect, it is important to judge defoliation averaged throughout the canopy because their feeding is concentrated only in the upper one-third,” Stewart writes in the UTcrops News Blog.

2. Spider Mites

Photo: John Obermeyer, Purdue Extension Entomology

Spider mites like hot, dry weather. “Development speeds up with temperatures above 90°F, and reproduction slows down at cooler temperatures,” says Farm Journal Associate Field Agronomist Missy Bauer. “It’s common to identify heavy spider mite pressure in fields that were densely populated with chickweed in the spring. Weeds provide a food source for mites early in the season.”

3. Japanese Beetles

Photo: John Obermeyer, Purdue Extension Entomology

Japanese beetle adults like warm, sunny days. Watch for them when the temperature gets above 70°F but especially if it hits 85°F to 95°F. If the relative humidity reaches 60% or higher, then they do less flying and more feeding in localized areas.

4. Soybean Aphids

Photo: John Obermeyer, Purdue Extension Entomology

Soybean aphids can overwinter almost anywhere in the U.S. Summer temperatures determine whether aphids will become a problem for soybean growers. Temperatures above 90°F will help keep populations from building up to damaging levels.

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Darrell Smith


John Obermeyer, Purdue Extension Entomology

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