NPIPM:Calomycterus setarius (soybean)
Authors: Buyung Hadi, Jeffrey Bradshaw and Ken Ostlie
The imported longhorned weevil, Calomycterus setarius, is native to Japan. The weevil was first reported in the United States in New York in 1929. Since then it has spread west as far as Iowa and Nebraska.
Identification
The adult imported longhorned weevil is small, about 1.5 inch (4 mm) long, motley gray in color, with the body covered in short stiff hair. The weevil antennae appear elbowed.
Life Cycle and Seasonal History
The imported longhorned weevil is parthenogenic. It only produces females and a female weevil can lay eggs without mating.
Eggs are laid in the soil and hatch in 8-12 days. The ensuing larvae feed on the roots of native aster, clover, alfalfa, goldenrod and several species of grasses. The larvae pupate in the soil in early June. Adult weevils emerge from the soil in mid-June and start to feed on plant foliage. Imported longhorned weevil is flightless, but it is able to walk a considerable distance. Adult weevils feed on foliage of over 100 plant species, including many ornamentals, grain, forage and vegetable crops. The adults lay eggs around September. The weevil only produce one generation per year.
Plant Injury and Damage
The imported longhorned weevil is a rare pest on soybean. However,the emergence of adult weevils in June may coincide with seedling soybean availability in the field. Large population of weevils feeding on seedling soybean may alarm the growers. In the field, a weevil is estimated to consume 0.03 inch2 (0.21 cm2) of foliage per day. The weevils usually start with plants in the border rows and advance inward when the plants in the outer rows are completely defoliated. Because the weevils are flightless, the movement into soybean field is relatively slow. Most of the plants away from the edges grow faster than the rate of defoliation due to the weevils feeding activity, thus the damage is typically isolated on few outer rows. Even plants in the edges that are completely defoliated can compensate by growing more foliage since the feeding usually happen in the vegetative phase of the soybean growth. Nevertheless the delay in canopy development may result in lush weed growth around the affected plants. Both the delay in canopy development and high weed pressure may still result in decreased yield on plants in the outer rows.
Management Approaches
Scouting and Threshold
Mid-June through early July, a period where the adult weevils are emerging from the soil, is a critical period to scout for imported longhorned weevil since it coincides with the vegetative phase of soybean. Scout parts of the field that borders weedy areas.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com
