|Corn Leaf Aphid: Rhopalosiphum maidis (Fitch)|
|Description and Biology: Great numbers of corn leaf aphids often infest the whorl and underside of leaves of sorghum. This dark bluish-green aphid is 2 mm long, oval in shape, with black legs, cornicles, and antennae. There are winged and wingless forms. Females give birth to living young without mating. A generation requires about seven days.|
|Symptoms and Damage: The corn leaf aphid most frequently is found deep in the whorl of the middle leaf of pre-boot sorghum, but also on the underside of leaves, on stems, or in panicles. Young and adult corn leaf aphids feed on plant phloem but do not inject toxin as do greenbug and yellow sugarcane aphid. The most apparent feeding damage is a yellow mottling of leaves when they unfold from the whorl. Sometimes molds grow on the honeydew corn leaf aphids produce in abundance. Honeydew on the panicle can cause harvesting problems. The aphid also transmits maize dwarf mosaic virus.|
Monitoring: When abundant, corn leaf aphids easily are seen within the whorl of sorghum plants. The whorl leaf can be pulled from the plant and unrolled to detect aphids when numbers of aphids are low. However, this insect rarely is damaging to sorghum. Consequently, sampling procedures and damage assessment information are not available. In fact, corn leaf aphids play a beneficial role. This aphid is an important host for the development of beneficial insects that are helpful in suppression of greenbug and other insect pests of sorghum. Often the aphid becomes abundant, but because it does not inject toxin as it feeds, rarely causes important damage. Also, because it prefers to live and feed in the whorl of sorghum, corn leaf aphid numbers decline rapidly after panicle exertion (emergence) from the boot. Beneficial insects that increase in abundance because of corn leaf aphids remain to feed on other insect pests.
Management: Sorghum plants generally can tolerate many corn leaf aphids without significant damage. Control of corn leaf aphids seldom is justified. Although aphids may be abundant, yield losses rarely occur. Yield losses have occurred only where corn leaf aphids cause stand loss of seedling plants, but this is rare. Occasionally, corn leaf aphids on a few plants in a field will become so abundant that panicle exertion and development are hindered. Although control of this aphid is not needed, it and other aphid pests can be controlled with organophosphates, especially systemic ones.