How to Manage Pests
UC Pest Management Guidelines
The adults are relatively small beetles, 0.13 to 0.2 inch (3.5 to 5 mm) in length, somewhat teardrop or triangular in shape, and dull-colored with white, reddish, or black markings. The eggs may be glued to the bean or the pod (cowpea weevil), glued to green pods (broad bean weevil), or laid loosely among beans or through cracks in the pods (bean weevil). The larval and pupal stages are spent inside the bean. The cowpea weevil is perhaps the most common of the weevils in California. Infestations can begin in the field. Adults move to bean fields from trash beans left in sacks, harvesters, planters, or feed areas. The cowpea weevil readily attacks dried beans; thus this weevil can be a serious storage pest.
Bean weevil infestations can also start in the field and may also originate from trash beans. As with the cowpea weevil, bean weevil will attack dried beans and can be a serious pest in stored beans. Broad bean weevil infestations also start in the field, but this pest is not a storage problem.
The larval stage of the weevil pests of dry beans tunnel and develop within the beans. They may consume nearly the entire bean contents. Pupation occurs in the beans and adults emerge through a round hole in the seed coat. Damage is a combination of the feeding and contamination.
Sanitation offers the most practical means of control. Because field infestations originate from beans, eliminate potential sources of weevils in production areas. Potential sources of weevils include broken sacks of seed beans left over from planting; seed beans left in planting hoppers; cull beans used in animal feed programs in a production area; small collections of beans remaining on or in a harvester following harvest; and small piles of beans remaining in or around the field after harvest or in a warehouse area.
Monitoring and Treatment Decisions
Field survey methods have not been developed, and insecticide applications during the production season have not provided effective control. Fumigation of beans at the warehouse site is imperative when infested beans are being brought in from the field. Fumigants are registered for this use. Fumigation of cull beans that are known to be infested may be desirable before releasing the culls for animal feed within a production area.
UC IPM Pest Management Guidelines:
UC ANR Publication 3446
L. D. Godfrey, Entomology, UC Davis
R. F. Long, UC Cooperative Extension, Yolo County