Early-season soybean pests often arrive before growers expect them.
Bean leaf beetle populations often peak just as seedlings emerge. Around the same time, soybean aphids, having migrated off alternative hosts, arrive looking for a new home.
Because of this early dual threat, timely scouting and management decisions are critical to protecting crops.
Early scouting and soybean aphid control
Seed treatments can help protect against early-season pests, but that protection often declines before soybean aphids begin colonizing fields, making soybean aphid scouting the most reliable way to determine when intervention is needed.
Monitor fields regularly and apply insecticide only when populations reach the soybean aphid economic threshold of 250 aphids per plant on roughly 80% of plants, with populations increasing. This provides a five- to seven-day window for treatment before populations reach levels that can cause economic damage.¹
This helps you avoid unnecessary applications while still protecting yield when populations necessitate it.
What do soybean aphids look like?
Soybean aphids are small, yellow-green insects that cluster on stems and the undersides of leaves.
Soybean aphids often establish colonies on the newest leaves and terminal buds, so these areas should be checked first. You may also notice indirect indicators of aphid activity. Lady beetles are aphid predators, and their presence can signal nearby aphid colonies. Ants may also indicate infestations, since they feed on the honeydew soybean aphids excrete and often protect aphid colonies from predators.
Sticky leaves, honeydew or shed aphid skins can also signal growing populations.
Insecticides for soybean aphids
When the economic threshold for soybean aphid is reached, timely control measures are needed to prevent yield loss.
Be aware that some foliar insecticides can kill not only aphids but also beneficial predators that suppress aphid populations. This disruption of natural enemies may lead to aphid resurgence later in the season or outbreaks of secondary pests.²
Using selective insecticides can help maintain beneficial insects while still providing effective soybean aphid control. Regional pest forecasting maps can also help growers anticipate outbreaks and better time soybean aphid insecticide applications.
Early scouting and bean leaf beetle control
Economic injury from bean leaf beetle feeding early in the season is relatively uncommon because soybeans can tolerate moderate defoliation. However, treatment may be warranted when leaf feeding reaches about 15% defoliation during reproductive stages and beetles are still actively feeding in the field.³
Scouting early is key to proactively gauging your crop’s level of infestation.
Scouting and identifying bean leaf beetle damage
Bean leaf beetles are typically yellow with black markings, but different morphs can be gray, brown, red and orange too. The most common traits shared by the morphs are a black triangle behind their thorax and six black spots with a black band around their wings.
The larvae will damage roots, and adults will feed on leaves and pods. Adult damage will look like small, round holes in the leaves.
Fields that emerge first should be prioritized when scouting, as they often attract large numbers of overwintering bean leaf beetles. Early-planted soybeans are particularly vulnerable because adult beetles are already active when seedlings begin to emerge.
Growers can also track beetle activity using degree-day models that estimate emergence relative to crop development. These models sum up daily average temperatures beginning around soybean emergence and can help predict when first-generation adult beetles are likely to appear in fields.
Insecticides for bean leaf beetle control
Before flowering, bean leaf beetle insecticide treatment is typically recommended when defoliation reaches 30% and beetles are still present in the field. After flowering, the threshold decreases to 20% defoliation, as plants become more sensitive to leaf loss.⁴
Heavily infested fields can sometimes act as trap crops, concentrating beetles in a single area and allowing early intervention before populations spread.
Early-planted soybeans, fields with a history of high bean leaf beetle pressure or those at risk for bean pod mottle virus may benefit from insecticidal seed treatments. Foliar applications of Fastac® CS at 2.8–3.8 fl oz/a can also provide effective control of bean leaf beetles.
Experts are available to help you make your early soybean pest control decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
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Endnotes
- Ohnesorg, Wayne, and Thomas Hunt. Soybean Aphid Scouting and Management. University of Nebraska–Lincoln Extension, CropWatch, 2 Aug. 2023, https://cropwatch.unl.edu/2023/soybean-aphid-scouting-and-management/
- Dominic D. Reisig. “Check Fields for Soybean Aphid.” NC State Extension Soybeans, North Carolina State University Extension, 19 Aug. 2025, https://soybeans.ces.ncsu.edu/2025/08/check-fields-for-soybean-aphid/
- Krupke, Christian, and John Obermeyer. “Bean Leaf Beetle Leaf and Pod Feeding: Some High Beetle Numbers and Damage.” Pest & Crop Newsletter, Purdue University Extension, 3 Sept. 2021, https://extension.entm.purdue.edu/newsletters/pestandcrop/article/bean-leaf-beetle-leaf-and-pod-feeding-some-high-beetle-numbers-and-damage/
- Koch, Robert, and Bruce Potter. “Bean Leaf Beetles in Soybean: Biology and Early Season Management.” Minnesota Crop News, University of Minnesota Extension, 16 June 2022, blog-crop-news.extension.umn.edu/2022/06/bean-leaf-beetles-in-soybean-biology.html.
