Reducing the abundance of leafhoppers
and thrips in a northern
California organic vineyard through maintenance
of full season floral diversity with summer cover crops
Clara I. Nicholls*, Michael P. Parrella
and Miguel A. Altieri
Abstract
1 Maintenance of floral diversity throughout
the growing season in vineyards in the form
of summer cover crops of buckwheat (Fagopyrum esculentum Moench) and
sunflower (Helianthus annus Linnaeus),
had a substantial impact on the abundance
of western grape leafhoppers, Erythroneura elegantula Osborn (Homoptera:
Cicadellidae), and western flower thrips, Frankliniella occidentalis
(Pergande) (Thysanoptera: Thripidae),
and associated natural enemies.
2 During two consecutive years, vineyard
systems with flowering cover crops were characterized
by lower densities of leafhoppers and thrips, and larger populations
and more species of general predators,
including spiders.
3 Although Anagrus epos Girault (Hymenoptera:
Mymaridae), the most important leafhopper
parasitoid, achieved high numbers and inflicted noticeable mortality
of grape leafhopper eggs, no differences
in egg parasitism rates were observed between
cover cropped and monoculture systems.
4 Mowing of cover crops forced movement
of Anagrus and predators to adjacent vines
resulting in the lowering of leafhopper densities in such vines.
5 Results indicate that habitat diversification
using summer cover crops that bloom most of the growing season, supports
large numbers of predators
and parasitoids
thereby favouring enhanced biological control of leafhoppers and thrips
in vineyards.
