Pest Profile

The corn leaf aphid, Rhopalosiphum maidis, frequently infests sorghum at the whorl stage. This aphid ranges in color from dark bluish-green to pale yellow, depending on temperature, darker forms being associated with cooler conditions. Key identifying features are the dark legs and cornicles, relatively short antennae, and feeding on the upper leaf surfaces exclusively, preferring the upper parts of the plant. Greenbugs, in contrast, have pale legs and cornicles, antennae almost as long as the body, and feed exclusively on the undersides of sorghum leaves, preferring leaves on the lower parts of the plant. Initial winged migrants arrive on the wind from southerly latitudes (or earlier planted corn fields) and initiate colonies deep in the whorl where they are detectable only by pulling out the central leaf and unrolling it. Observing the activities of lady beetles is the easiest way to locate infested plants at this stage. Although large colonies may remove substantial volumes of sap, they do not cause direct plant injury. Their feeding occurs largely during the period of strong vegetative growth when plants are most able to compensate for these losses. Usually, corn leaf aphid colonies disappear before the panicle emerges fully, the majority of nymphs maturing into winged adults and dispersing in search of other plants in suitable growth stages.