Description

Aphids found on Arkansas field corn are minute (<1/8 in. long) blueish-green insects (Photo 5-14). Clear membranous wings may be present but wingless forms are more common. Aphids occur in colonies which contain different size nymphs and adults. As the newly born nymphs increase in size, molting occurs and the white exoskeleton is left on the leaf surface.

Distribution, damage and impact

Aphid species that attack field corn occur throughout the state and are often found in the whorl of the plant during mid to late summer. Late planted corn is generally more susceptible to damage from aphid feeding. Aphids feed by inserting their stylet or beak into the plant tissue and removing plant sap. Large amounts of sap are removed and the partially digested contents are excreted onto the plant surface in the form of a clear sticky honeydew. A dark grey mold may later form on the honeydew. The level of injury in Arkansas field corn appears to be minimal and generally does not require management. Aphids also transmit viral diseases but aphid control is not effective in viral disease management.

Life History

Aphids are capable of overwintering on alternate host plants in Arkansas. Also, winged aphids are carried into the state on winds coming from more southern areas each spring. Adults colonize grassy hosts and field corn seedlings and reproduce asexually through the summer. Development of nymphs is rapid and many generations occur each season. As temperatures peak during mid to late summer, reproduction rate declines. Thus early planted corn that matures in August generally is less susceptible to aphid population increase. Later planted corn, however, may experience large aphid populations in early fall. Also, foliar insecticides applied for corn borer management in mid to late summer may reduce beneficial insect population and result in aphid population increase.

Management

Early planted corn rarely harbors large aphid populations. In late planted corn, aphid populations may be very high, but when this population buildup occurs on maturing corn, aphid management will likely have little economic benefit. Excessive aphid populations on actively growing corn my be managed with foliar insecticides but the benefits may be very limited. Numerous beneficial organisms affect aphids including naturally occurring insect pathogens, parasites and predators and insecticide use may reduce their effectiveness. Some corn hybrids possess some level of resistance to the aphid.

Insecticide recommendations for aphids on field corn

See Table 5-2 for insecticide recommendations current at time of publishing. Current updated recommendations can be found in the Cooperative Extension Service publication MP-144 and on the world wide web at WWW.cdms.net/manuf/default.asp. Always follow instructions on pesticide labels.