Three-Cornered Alfalfa hopper, Spissistilus festinus (Say) [Homoptera: Membracidae], is occasionally found in North Coast vineyards where its injury may be mistaken for symptoms of leafroll virus. It can be an economic pest in leguminous crops. It also feeds on fruit trees, shrubs, herbs, and grasses. Three-cornered alfalfa hopper and buffalo treehopper (S. bisonia Kopp and Yonke) are common and widespread treehopper species; however, only three-cornered alfalfa hopper inflicts characteristic damage to grapevines.
Three-cornered alfalfa hopper plant damage has only been described for alfalfa and other legumes; however, it is probably similar to what occurs on grapevines. Like grape leafhopper, it has piercing-sucking mouthparts. Its random puncturing of the blades and stems of vines does not cause significant damage. Damage to grapevines result, however, when there is a concentration of feeding punctures in a continuous line on a petiole or lateral stem that girdles these structures. Girdling is caused by late instar nymphs more than by adults. The restriction of water and nutrients to the leaf blade distal to the girdle reduces chlorophyll production. Anthocyanins become the dominant pigment, causing reddish leaves like those caused by leafroll virus.
Three-cornered alfalfa hoppers are a minor pest in California's North Coast vineyards. Treatment of vines, cover crops in row middles, or weedy areas surrounding vineyards is not necessary.
