Threecornered Alfalfa Hopper

The threecornered alfalfa hopper adult is a green, robust, wedge-shaped insect with clear wings. The body is about 0.25 inch (6.4 mm) long, is higher and wider at the head and tapers towards the end. This insect gets its name from the hardened triangular (three-cornered) area over the thoracic area as seen from above. It has piercing-sucking mouthparts. Nymphs are grayish white and soft bodied, with a line of saw-toothed spines on their backs. Adults are mobile whereas nymphs cannot fly and are confined to the lower portions of the plant.

Adults feed on numerous plants and have been recently shown to transmit red blotch in grape vineyards. In alfalfa, threecornered alfalfa hoppers can be found year-round. In the low desert, there are two population peaks for adults: one in late July to early August and a larger second peak in September to early October. In the San Joaquin Valley, threecornered alfalfa hoppers numbers usually peak in late September and October. They are starting to become more numerous in the Sacramento Valley, usually late August to early September. There are three to four generations per year in Southern California.

Adults and nymphs of the alfalfa hopper usually feed at the base of the alfalfa plant near the crown by inserting their mouthparts into stems and sucking out juices. Injury is also caused when adult female hoppers insert their eggs into stems. Feeding and egg laying can girdle stems, causing the portion of the plant above the girdle to turn red, purple or yellow.

Monitor for adults using a sweep net and by visually watching for stems that show the characteristic reddish discoloring and girdling at the base of the plant. Nymphs are difficult to find because they are at the base of the plant and cannot fly. Occasionally damage is severe enough from the hoppers to justify control measures, especially if other pests, such as armyworm are also injuring the crop. However, this insect does not inject toxins, unlike the Empoasca, so they are not as damaging as some leafhopper pests.

Biological control of threecornered alfalfa hopper is generally limited to the first three nymphal instars, which remain inactive lower on the alfalfa plants. Predators include assassin and nabid bugs. Adult hoppers typically escape predation due to their activity and heavy sclerotization (hardening of the exoskeleton), which nymphs lack.

Overwintering threecornered alfalfa hopper adults and newly hatched nymphs can be found in weedy margins (e.g. vetch) of alfalfa fields in the early spring. Manage these areas to reduce threecornered alfalfa hopper populations that can later migrate into alfalfa fields. Early harvest will also help manage this pest.

No specific threshold numbers have been developed for threecornered alfalfa hoppers. However, in the Sacramento Valley area, an average of four leafhopper adults per sweep over 15 days did not cause economic losses to alfalfa hay; but, in the south valley, 10 to 12 hopper adults per sweep significantly reduced both alfalfa yield and quality. These numbers give a range of hopper counts for possible injury to the alfalfa crop and should be combined with observations of damage to determine whether to treat with insecticides listed below. Early spring alfalfa stubble insecticide applications after the first cutting are a viable option to manage threecornered alfalfa hoppers long term in outbreak years.