Occasional and Non-Economic Small Grains Pests
Schizaphis graminum Rondani
Appearance and Life History
Greenbug is a small, light green aphid, about 1/16 inch (1.6 mm) long when full grown. It has a narrow, dark green stripe down the center of its back. Its cornicles (the two small tube-like projections from its posterior end) and legs are the same color as the body. However, the tips of the cornicles and feet are black.
Greenbug may be winged or wingless. The winged form is slightly larger. Also, the winged greenbug has a brownish-yellow head and black lobes on the back of its thorax (the area immediately behind the head). Often, greenbug is confused with the very similar appearing corn leaf aphid. Corn leaf aphid is blue-green and has a black head, legs, feet, and cornicles.
The reproductive potential of greenbug is very high. Unlike most insects, but typical of aphids, this aphid gives birth to live young. The young develop into reproducing adults in about 7 to 15 days.
Greenbug uses its piercing-sucking mouthparts to suck plant juices. It also injects toxins into the plant while feeding. The toxins cause the death of plant tissue, and where injected, a red spot develops. As feeding increases, the red areas increase in size, and eventually, infested leaves may turn brown and occasionally die.
If greenbug is found in significant numbers in a small grain field, in 2 locations within 5 areas of the field carefully examine the underside of the leaves on one linear foot (30 cm) of stems and count and record the number of greenbug found. Calculate the average number of live adults and nymphs per linear foot (30 cm) of stems. Note the number of parasitized greenbug (gray to brown and balloon-shaped) and any beneficial insects, such as lady beetle adults and larvae and lacewing larvae on plants. Also determine the stage of plant development and the extent of greenbug damage.
Appearance and Life History
Several species of thrips may be found in small grains. Typically the nymphs are light colored and the adults, with feather-like wings, are darker. These slender insects are about 1/16 inch (1.6 mm) long.
Both winged adults and immatures feed by penetrating leaf cells and sucking out the contents. Minute, longitudinal, whitish scars become so numerous that entire leaves look grayish and desiccated. Most feeding occurs behind leaf sheaths or on the underside of lower leaves. Damage is usually noticed only under extended hot, dry weather conditions when plants are moisture stressed. Gusty winds during these periods will further desiccate plant tissue and compound thrips injury.
Thoroughly examine discolored plants for thrips and their damage. Estimate the extent of damage in the field.
Small Grains Insect Control Recommendations: E-series 220-W (PDF)
No management guidelines have been established for thrips in small grains. Vigorous growing plants with adequate soil moisture can tolerate thrips damage. If dry conditions are expected to continue, plants are grayish and wilting, and thrips are present, then a treatment may be justified.
If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.