Alfalfa weevils aren’t the only insect pest being found in alfalfa fields this spring. Reports of aphids, particularly cowpea aphids and pea aphids, have been made around the state. This article will discuss identifying the common aphid species found in Iowa as well as scouting and management recommendations for aphids in alfalfa.
Aphids are common insects to see in field crops, especially in alfalfa. In Iowa, there are at least four aphid species that can persist on alfalfa. A recent report of pea aphids near Clarion, IA from field agronomist Angie Rieck-Hinz prompted me to write this article. Learning to distinguish aphids in alfalfa takes a little practice, but is worth knowing for making sound treatment decisions.
Soybean aphid
This is the only species in Iowa that will colonize soybean. Scout weekly from plant emergence until seed set. Aphids prefer to feed on the undersides of leaves and will establish on the newest leaves. If a large colony develops, they will feed on stems. Initial infestations are patchy and located near field edges, but winged aphids can quickly disperse within and between fields. Commercial fields that have reached uniform infestation should be closely monitored in August.
