How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Aphis craccivora
(Reviewed 11/06, updated 4/08)
In this Guideline:
Cowpea aphid has been a long time resident of alfalfa in California as well as other states. In the Central Valley, populations are highest from February to April; numbers peak from October to January in the desert; and in the San Joaquin Valley, populations can reach treatable levels in August and September. Cowpea aphids are a sporadic pest in the Intermountain Region and require treatment in some years – mostly in spring, but damage can occur at other times during the growing season.
Cowpea aphid injects a powerful toxin into the plant while feeding and, when populations are large, this can stunt or kill plants. While feeding, this aphid produces a considerable amount of honeydew upon which sooty mold grows. The black sooty mold reduces photosynthesis and may make leaves unpalatable to livestock. The honeydew also makes the alfalfa sticky, which causes problems with harvest.
There are no known varieties of alfalfa that are resistant to cowpea aphid and economic thresholds have not been developed specifically for this pest. Treatments may be necessary if large populations are present. Border harvesting or strip cutting can be important for preserving natural enemies.
Biological Control (View photos of
Use border-strip cutting during harvest to help maintain populations of parasites and predators within the field. For more details, see BORDER-STRIP HARVESTING.
Organically Acceptable Methods
The use of biological and cultural controls are acceptable on organically certified crops. Organically certified insecticides such as azadirachtin (Neemix), neem oil (Trilogy), and pyrethrin (PyGanic) are registered for use on alfalfa to control aphids. Studies conducted in California, however, have shown that at best they provide some suppression of populations but do not control them.
Monitoring and Treatment Decisions
Aphid infestations in a field are typically patchy, especially an early infestation. Stems on alfalfa plants in infested areas are often completely covered with aphids whereas plants in other areas of the field may appear aphid-free. Because of the spotty distribution of cowpea aphid infestations, spot treatments may be feasible, especially if the infestation is on the field border.
On dormant alfalfa, pay close attention to plants as they begin breaking dormancy. If shoots fail to grow normally and cowpea aphid is present, consider control measures.
Start to monitor fields in February for cowpea aphid and continue to monitor this aphid through fall at which time monitoring can be combined with that of blue alfalfa and pea aphid as described in APHID MONITORING. (During summer months, monitoring of cowpea aphid can be combined with that of spotted alfalfa aphids.)
Record counts on a monitoring form.
No guidelines or economic threshold levels have been established for cowpea aphid in alfalfa. Until economic thresholds are developed for the cowpea aphid, use the following thresholds, which were developed for the blue alfalfa aphid:
UC IPM Pest Management Guidelines:
Insects and Mites