South Georgia Crop News

Crop News Covering Crisp, Turner, Worth, and Wilcox Counties

Cowpea Curculio

The following information regarding cowpea curculio was provided by Dr. Stormy Sparks, Dr. David Riley, and Jenna Kicklighter.

 

Background on the pest

The cowpea curculio, Chalcodermus aeneus, occurs throughout the Southeastern United States. While this pest will feed on and injure multiple legumes, its preferred host is cowpeas. We occasionally get reports of it in snap beans, but this is relatively rare and frequently limited along the field edge. Adults are small black weevils with deeply pitted elytra and a coarsely punctate thorax. Adults overwinter in protected habitats around fields and enter cowpea fields starting around April. Reproduction occurs in the pods of cowpeas. As with most weevils, females eat holes into the pods and seeds and then turn around and place eggs within these holes. After oviposition, the hole is filled resulting in a wart-like raised area on the surface of the pod. Feeding holes are not filled and remain as open punctures into the pod. Once an egg is placed into a pod, the eggs hatch and all larval development (4 instars) is completed within the pod. The 4th instar larvae eats its way out of the pod, drops to the ground, and burrows 1 to 3 inches down before forming a pupal cell where it pupates and eventually emerges as an adult. The entire life cycle from egg to adult requires 30 to 40 days. Curculio adults can be difficult to find in fields and will play dead when picked up. If you enter a field and readily see curculio adults, you have a very heavy infestation. Curculios are reported to rarely fly (although I question this), thus, rotation away from infested areas is recommended (definitely avoid sequential plantings in the same area).

Management of Cowpea Curculio

As with most weevils, curculio management is challenging under the best situations. Because most of the life cycle is completed in a protected environment (inside of pods) the only stage readily available for control with insecticides is the adult. Effective control requires that you kill the adults before they oviposit. This generally requires a preventive spray program with a highly effective insecticide. Historically this has been accomplished with sprays started at pin-stage (or basically first bloom) and repeated for four applications on a 4 to 5 day schedule. Organophosphate and similar products were used until resistance reduced their efficacy. Pyrethroids (Brigade, Karate, and many others) replaced these products over a decade ago and provided excellent control until recently (first field failures occurred about 3 years ago). Recent efficacy trials conducted at UGA and grower experience have confirmed the greatly reduced performance of the pyrethroid insecticides and have not been able to identify any labeled alternative product with satisfactory efficacy. Even experimental insecticides have offered little promise. Current in-field recommendations include pyrethroid plus lannate (or a labeled synergist) tank mixes; however, under even moderate pest pressure experience suggests that no labeled insecticides will provide adequate control. We continue to look for efficacious insecticides and work toward obtaining labels, but this does not look promising for the short term.

We are evaluating alternative approaches, such as post-harvest treatments to reduce overwintering populations, but these are experimental approaches and their potential efficacy is unknown. A trap has also been developed, but its purpose is to monitor periods of adult activity. It is not a control method.