Leafhoppers

Several species of leafhoppers may occur on cotton. The southern garden leafhopper is most common in desert valleys, and the potato leafhopper is most common in the San Joaquin Valley. Only these two species cause economic damage. The potato leafhopper generally appears in cotton fields near potato fields in the Arvin-Edison area of Kern County and near the Sierra Nevada foothills in northern Kern, Tulare, and Fresno counties. Outbreaks of the southern garden leafhopper are most common near sugarbeet fields in the Imperial Valley.

Both species are identical in appearance; they can only be distinguished by examining their reproductive organs. Adults are pale green, wedge shaped, 0.12 inch (3 mm) long, with inconspicuous white spots on the head and pronotum. Adults fly or jump when disturbed. Nymphs (immatures) also have green wedge-shaped bodies and run rapidly forward, backward, or from side to side when disturbed. Their unique movement plus their bright color and shape distinguishes them from lygus bug nymphs and other slower moving insects like aphids.

Adults and nymphs suck sap from veins on the undersides of mature leaves, mostly on the lower half of the plant. The midrib veins become roughened. Affected leaves may become distorted, leathery, and develop yellow or red blotches. Though rare, severe infestation may cause plants to shed squares and small bolls. Larger bolls may turn soft and spongy, and fail to mature. Other species cause leaf stippling.

Natural enemies usually keep leafhoppers from building up large populations in cotton. However, if large numbers migrate to cotton from other hosts, treatment may be needed if extensive symptoms appear.

There is no treatment threshold for leafhoppers. Before applying an insecticide, check for swollen, lumpy main veins on a sample of injured leaves to make sure the field symptoms are actually caused by leafhoppers.