Soybean
Bean Leaf Beetle
Cerotoma trifurcata
Insect
In a Nutshell
- Feeding damage on roots, root nodules, foliage and developing pods.
- Small holes scattered over the leaves.
- Scarred appearance of pods.
- Reduces yields and seed quality.
- Dark yellow to red colored beetles, with rectangular marks on their wings.
Soybean
Symptoms
Larvae and adults feed on roots, root nodules, cotyledons, leaves (often the underside) and pods. The rupture of root and vascular tissues might reduce nitrogen fixation. Damage on leaf blades appear as small, almost round holes scattered over the leaf. Pods fed upon have a scarred appearance. Yields and seed quality are reduced due to feeding damage on pods. Damaged pods hold an entry for microorganisms like fungi and bacteria. If Cerotoma trifurcata occurs early in the season, it might lead to seedling injury, defoliation and seed discoloration.
Recommendations
Organic Control
At the moment, no effective biological control of the pest is known.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. If the damage is bound to cause significant yield decrease, consider applying chemicals. Insecticides of the group of pyrethroid, lambda-cyhalothrin or dimethoate can help to reduce population of the pest.
What caused it?
The adults are about 6 mm long and dark yellow to red in color. Their wings can be covered with characteristic rectangular marks and they have a black triangle in the neck region. Adult females lays eggs in the upper two inches of soil near the plant stems. One female lays 125 to 250 eggs during her life. The eggs hatch in four to 14 days depending on soil temperature. The larvae are white colored with a dark brown or black head. Adults overwinter in various habitats around soybean fields. The bean leaf beetle serves as a vector for several types of viruses.
Preventive Measures
- Plant later to reduce damage.
- Count insects and assess plant damage early in the season.
- Row covers can provide a physical barrier to these insects.
- Plow deep and avoid planting other legumes nearby.
- Perform large crop rotation.
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