Individual study: Relative impact of spider predation and cover crop on population dynamics of Erythroneura variabilis in a raisin grape vineyard
Hanna R., Zalom F.G. & Roltsch W.J. (2003) Relative impact of spider predation and cover crop on population dynamics of Erythroneura variabilis in a raisin grape vineyard. Entomologia Experimentalis et Applicata, 107, 177-191
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Pest regulation: Plant or maintain ground cover in orchards or vineyards
A replicated, randomized, controlled study in 1991–1992 in an irrigated vineyard in the San Joaquin Valley, California, USA, found more spiders in plots with cover crops, compared to bare soil, between the vine rows. Pest regulation: Similar percentages of Erythroneura variabilis leafhopper eggs were parasitized in plots with or without cover crops between the vine rows (5–90%). Pest numbers: Similar numbers of leafhoppers were found in plots with or without cover crops between the vine rows (2.9 vs 2.4 nymphs/leaf; 19 vs 18 adults/trap, 9–45 vs 9–31 eggs/leaf). Natural enemy numbers: More spiders were found in plots with cover crops, compared to bare soil, between the vine rows (9 vs 6 spiders/sample), but there was no difference in spider species composition (data not reported). Methods: Cover crops (1.5 m width) were grown between the vine rows (3.7 m width) in three plots, and bare soil was maintained through cultivation between the vine rows in three control plots (two vine rows/plot, 110 m length). The cover crops (Avena sativa oats, Vicia sativa common vetch, and V. benghalensis purple vetch) were seeded in November 1991, mown to 20 cm height in April 1992, tilled in July 1992, and cultivated thereafter. Leafhoppers were sampled every 14–18 days in May–September 1992 (nymphs on 24 grape leaves/plot, adults on three yellow sticky traps/plot, eggs and egg parasitism on five grape leaves/plot). Spiders were sampled every month by shaking the vine canopy for 10 seconds into funnels (0.58 m2 funnels, two samples/plot).