Bean leaf beetle is among the top five most-damaging invertebrate soybean pests, costing growers nearly 3.1 million bushels in 2023.¹
This pest is especially damaging early in the season and can cause severe damage to both soybean leaves and pods. Additionally, bean leaf beetles transmit bean pod mottle virus (BPMV), a disease that in its own right can cause yield losses as high as 52%.²
Early identification and management of bean leaf beetles in soybeans is critical to prevent this pest from opening a whole can of worries for your soybean crop.
We’ve put together a brief guide to help you understand bean leaf beetle life cycle, identify signs of infestation and know which control methods can help minimize damage.
Bean leaf beetle life cycle
Overwintering adult beetles emerge in early April and mate, typically using alfalfa or other legumes as their host. Bean leaf beetles move into soybeans as soon as plants have emerged, and their populations usually peak around soybean emergence.
As mature bean leaf beetles infest soybeans, they reproduce by laying eggs at the base of the plants. The subsequent larvae feed on soybean roots. The first generation of adult beetles emerges within three weeks and generally starts feeding on soybean around July.
Bean pod mottle virus transmission is generally most damaging to soybeans when it occurs during soybean vegetative growth stages.
Bean leaf beetle populations operate in boom and bust cycles. As you’d expect, the pest population increases dramatically during boom phases when the beetles can feed on abundant crops. Cold winters, which bring a lack of food and harsh environmental conditions, are considered the bust phase and are thought to keep beetle populations in check.
Every spring, ICM News publishes a prediction for overwintering mortality.
Symptoms of bean leaf beetle damage
Most bean leaf beetle damage is caused by adult beetles feeding on soybean leaves (but larval stage bean leaf beetles can damage soybean roots, too). High populations of adult bean leaf beetles can destroy small cotyledons and completely defoliate the first true leaves, killing young seedlings. Excessive defoliation can reduce the yields of soybean plants.³
Adult beetle damage on leaves consists of large, round holes, 3 to 4 mm in diameter, created from beetles feeding on the undersides of leaf surfaces.
Adults beetles feed on the outer surface of bean pods during pod set. Pod clipping may result in a complete loss⁴ and also cause enough damage to provide an entry point for virus and disease.
Scouting for bean leaf beetles in soybeans
Scout for bean leaf beetles in soybeans anywhere from seedling emergence until R7.
When scouting, you can estimate the level of infestation by:
- Using a visual count on very small soybeans
- Sweeping a net or ground cloth to sample larger plants. In this method, take a 20-sweep sample in five areas of the field and count the number of bean leaf beetles per sweep to determine if pests are actively feeding in your soybean field.⁵
How to get rid of bean leaf beetle
Learn the different control strategies available for early-planted soybeans.
Cultural practices
Removing crop residue and using tillage to control weeds that could harbor bean leaf beetles can help reduce infestations.
Chemical control
There are chemical control options available to combat bean leaf beetles in soybeans.
To determine whether treating the infestation chemically is economically feasible, you need to calculate your bean leaf beetle infestation.
This can be done by randomly selecting five sampling sites across the field and walking down 15 to 20 feet of row at each site, counting beetles and plants, and noting whether the growing point has been damaged or killed without disturbing the plant.
A general rule of thumb provided by University of Minnesota Extension suggests the following thresholds for chemical treatment.
- For vegetative plants (before flowering), treat if beetles are present and defoliation reaches 30%.
- For reproductive plants (flowering to pod-fill stage), treat if beetles are present and defoliation reaches 20%.
- If pod injury reaches 10% due to bean leaf beetles or other pod-feeding insects, treatment is necessary and aggressive treatment is recommended if populations are large and pod clipping is occurring.⁶
Always ensure you speak with experts who have area-specific information. Bean leaf beetles in soybeans can be managed, and your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative can help you develop a game plan.
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Endnotes
- Sisson, Adam, et al. “Soybean Invertebrate Loss Estimates from the United States — 2023.” Crop Protection Network, 7 Aug. 2024, cropprotectionnetwork.org/publications/soybean-invertebrate-loss-estimates-from-the-united-states-2023. Accessed 8 Jan. 2025.
- Garcia Rodriguez, Raymond, and Lindsey Thiessen. “Bean Pod Mottle Virus.” NC State Extension Publications, 2 Sept. 2020, content.ces.ncsu.edu/bean-pod-mottle-virus. Accessed 8 Jan. 2025.
- Van Wychen Bennett, K., et al. “Bean Leaf Beetle.” VegEdge, University of Minnesota, vegedge.umn.edu/insect-pest-profiles/bean-leaf-beetle. Accessed 8 Jan. 2025.
- Van Wychen Bennett. “Bean Leaf Beetle.”
- Krupke, Christian, and John Obermeyer. “Bean Leaf Beetle Pod Feeding On Late Maturing Soybean.” Pest & Crop Newsletter, Purdue University, 3 Sept. 2020, extension.entm.purdue.edu/newsletters/pestandcrop/article/bean-leaf-beetle-pod-feeding-on-late-maturing-soybean/. Accessed 8 Jan. 2025.
- Koch, Robert, and Suzanne Wold-Burkness. “Bean Leaf Beetles.” Extension at the University of Minnesota, 2024, extension.umn.edu/soybean-pest-management/bean-leaf-beetles. Accessed 8 Jan. 2025.
