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Extension > Agriculture > Crops > Soybean Production > Pest management > Treatment thresholds for soybean insects and mites

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Treatment thresholds for soybean insects and mites

Robert Koch, Extension Entomologist

The goal of this publication is to provide a summary of treatment thresholds to assist growers and agricultural professionals with pest management decision making. For information on pest identification and biology see the integrated pest management guide. When using insecticides, always read and follow label directions.

Pests Injury Threshold
Insects that attack seedlings
Cutworms Girdle or cut through young stems Treat if 20% of plants are cut, stand has gaps of 1 foot or more, and cutworms are present.
Potato leafhopper Remove plant sap and inject toxic saliva From emergence to two trifoliate leaves (V2), treat if populations exceed 1 leafhopper per plant or if seedling plants with dying leaves are present.
Insects and mites that attack vegetative and reproductive stage plants
Soybean aphid Remove plant sap Maintain scouting through R6.5 (pods and leaves begin to yellow), regardless of calendar date. Through R5 (seeds developing, but pod cavity not filled), use economic threshold of 250 aphids/plant (>80% of plants infested and populations increasing). Yield loss is possible into early R6 (pod cavity filled by seed). Though an economic threshold has not been developed for R6, large populations in early R6 may require treatment if plants are experiencing other stresses.
Bean leaf beetle

Japanese beetle

Foliage caterpillarsa

Grasshoppers
Defoliate soybean leaves Treat if defoliation from any combination of these or other defoliating insects reaches 30% in pre-bloom growth stages (V1 to R1) or 20% from bloom (R1) to pod fill (R6) growth stages.

A count threshold can also be used for grasshoppers. Treat if the number of adult grasshoppers reaches 20 per yd2 in field margins or 8-14 per yd2 within the field; or, treat when the number of nymphs reaches 25-35 per yd2 in field margins or 15-25 per yd2 within the field.
Twospotted spider mite Destroy leaf cells Treat if small colonies of mites and minor stippling can be seen in the middle canopy. Typically, there will be heavy mite populations and damage (stippling) present in lower canopy at this time. There may be an occasional plant with stippling in the upper canopy.
The presence of mite colonies and damage in the upper canopy require prompt treatment.
Insects that attack pods
Bean leaf beetle

Grasshoppers
Damage pods and seeds Treat if pod injury from any combination of these insects reaches 10%. Treat aggressively if populations are large and pod clipping is occurring.
Stink bugs Damage seeds Treat if the number of stink bugs (adults and nymphs greater than 1/4 inch) reaches 5 per 25 sweeps for soybean grown for seed or 10 bugs per 25 sweeps for soybean grown for grain.
aFoliage caterpillars include: cabbage looper, green cloverworm, saltmarsh caterpillar, thistle caterpillar, webworm, woolly bear caterpillar, and yellowstriped armyworm


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