Soybean
Broad nosed Weevils
Myllocerus sp.
Insect
In a Nutshell
- Notched leaf margins.
- Stunted plant growth.
- Light grey with dark patterns on wing covers and head of adult weevils.
Soybean
Symptoms
First visible symptoms of an infestation by the grey weevil are notched leaf margins. Adult weevils prefer to feed on the margins of new plants and proceed inward. Severely infected leaves can be completely defoliated. Healthy plants will recover from the feeding damage, but young seedlings will die at the time of flowering. Severe infestation might restrict plant growth. Affected plants can be easily pulled out.
Recommendations
Organic Control
Drench your soil with Bacillus thuringiensis ssp tenebrionis (Btt) @ 2.5 mg/lit. The bacteria can also be used in the root tip method. You dip the roots of your plant in the Btt dilution and air dry them before replanting in the soil. The mortality of the larvae is dependent on the maintenance of humidity and temperature. Apply neem cake @ 500 kg/ha at the time of the last plowing.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments, if available. Chemical treatment has only limited success for managing grey weevil as their eggs, larvae, and pupae are located in the soil. Adult weevils are also difficult to handle because of their ability to fly, hide and feign death. Problems arise with the development of resistance. You can spray quinalphos or chlorpyrifos at 20 days after sowing.
What caused it?
Symptoms are caused by both adults and grubs of the grey weevil, Myllocerus sp. Adult weevils are small and light grey in colour, with darker patterns on their wing covers and head. Females lay 360 eggs on average in the soil over a period of 24 days. After hatching, the larvae burrow into the soil where they feed on plant roots. The grubs then reproduce in the soil. Adult weevils will survive in winter, hidden under debris. Myllocerus sp. has a wide range of host plants from ornamental, vegetable to fruit species.
Preventive Measures
- Use the available resistant varieties.
- Monitor and detect the crops when new leaves start to grow for precaution.
- Frequent hoeing may disturb them and kill the grubs.
- Some sources have reported that planting pigeon pea as a trap crop would be effective.
- Adult weevils can be removed by shaking the tree/branches and putting them in a container of soapy water.
- Remove affected plants/branches and destroy them.
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