Description

Aphids found on Arkansas grain sorghum are minute (<1/8 in. long) blueish-green insects (Photo 1). 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 grain sorghum occur throughout the state. Among the aphids found on grain sorghum in Arkansas, the greenbug is generally the most damaging. 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 gray mold may later form on the honeydew. The level of injury in Arkansas grain sorghum is often low and beneficial organisms may provide sufficient control. 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 grain sorghum seedlings and reproduce asexually through the summer. Development of nymphs is rapid and many generations occur each season. Foliar insecticides applied for control of other insects may reduce beneficial insect populations and result in an aphid population increase.

Management

Excessive aphid populations on actively growing grain sorghum may 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 grain sorghum hybrids possess some level of resistance to the aphid.

Insecticide recommendations for aphids on grain sorghum

See Table 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.