Spider and Leafhopper (<I>Erythroneura</I> spp.) Response to Vineyard Ground Cover

Abstract

Ground cover is used in some vineyards to improve soil structure and help manage insect pests; previous studies have shown lower leafhopper (Erythroneura spp.) densities on vines grown with ground cover. We undertook a 2-yr study to determine why ground cover is associated with reduced leafhopper densities. Ground cover consisted of a fall-planted cover crop of purple vetch (Vicia benghalensis) and barley (Hordeum vulgare), which senesced in May and was replaced by a complex of resident vegetation comprised primarily of the grasses Echinochloa spp., Digitaria san guinalis, and Setaria spp., as well as common knotweed (Polygonum aviculare). We compared three treatments during the growing season: Cover, No Cover, and Cover/Exclusion. Cover/Exclusion was similar to Cover treatment but with barriers to impede arthropod movement between ground cover and vines. We measured leafhopper density and egg parasitism, spider density and diversity, and grapevine vigor, and found that mid-and late-season leafhopper densities were signiÞcantly lower in Cover versus No Cover. Neither leafhopper egg parasitism nor spider density on the vines or ground cover could explain these differences; however, grapevine vigor was signiÞcantly lower in Cover than No Cover, and provides the best correlation to leafhopper density. Late-season leafhopper density was highest in the Exclusion treatment but cannot be explained by changes in grapevine vigor. Individual spider species composition and density on the grapevine canopy varied signiÞcantly among treat ments: Trachelas pacificus (Chamberlin and Ivie) was higher in the Cover treatment, Hololena nedra Chamberlin and Ivie, Cheiracanthium inclusum (Hentz), and Neoscona oaxacensis (Keyserling) were lower in the Exclusion treatment, and Oxyopes spp. was higher in the Exclusion treatment. We suggest the lower densities of leafhoppers in the Cover treatment resulted from poorer host plant quality because of the competition between ground cover and grapevines. The higher late-season leafhopper densities in the Exclusion treatment may be due to changes in spider species composition, and subsequently, differences in rates of predation on leafhopper nymphs.

Influence of grapevine cultivars on the leafhopper Empoasca vitis and its egg parasitoids

“…Also, the infestation of grape leafhoppers (Erythroneura spp.) in North America was positively correlated with the vigour of the grapevines (Daane et al 1995;Costello and Daane 2003).…”

Ground-Dwelling Spider Fauna (Araneae) of Two Vineyards in Southern Quebec

“…Similarly, Pekár (1999) observed lower spider abundance under conventional spraying practices than under integrated pest management (IPM), and Brown et al (2003) documented higher spider diversity when apple trees were left unsprayed. Cultural practices such as tillage, ground cover, and intercropping also inßuence spider diversity and abundance by modifying the availability of habitat and food Carter 1999, Costello andDaane 2003).…”

Biological and cultural controls … Nonpesticide alternatives can suppress crop pests

“…Still, the beneficial role of cover crops with respect to natural enemies is not clear. It is likely that cover crops have a dual role, changing both the susceptibility of the vines to pests and the ability of the vineyard to support natural enemies, leading to a combined impact on pest densities (Costello and Daane 2003).…”