Evaluating the potential of buckwheat and cahaba vetch as nectar producing cover crops for enhancing biological control of Homalodisca vitripennis in California vineyards

• Buckwheat (BW) and vetch (V) enhanced parasitoid survival and fecundity.
• BW usually required 23–32 days from sowing to nectar-producing flowers.
• X. fastidiosa (Xf) infected and replicated in BW, V, sweet alyssum and coriander.
• H. vitripennis transmitted Xf between BW and grapevine in greenhouse and field.
• H. vitripennis successfully transmitted Xf from grapevine to V in the field.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) is a significant pest of grapevines in California due to vectoring Xylella fastidiosa Wells et al., Buckwheat (Fagopyrum esculentum Moench) and vetch (Vicia sativa L. cv. ‘cahaba white’) are potential nectar-producing cover crop plants in California vineyards that could enhance Gonatocerus ashmeadi Girault, a parasitoid of H. vitripennis. Three aspects of these 2 plant species were evaluated. (1) Effect on parasitoid fitness: In the laboratory, buckwheat and vetch enhanced survival of G. ashmeadi by 9 and 6 days, respectively, compared to water. G. ashmeadi offspring production was 81% and 142% greater when females were provided vetch or buckwheat, respectively, compared to water. Buckwheat decreased G. ashmeadi female offspring by 19% compared to water and vetch. (2) Nectar production phenology in southern California: From April through September, buckwheat required only 23–32 days from sowing to nectar-producing flowers. Vetch required an additional 14–33 days to produce extrafloral nectar during June–August. The range in length of the nectar producing period between August 2007 and November 2007 was 41–52 days and 163–164 days for buckwheat and vetch, respectively. (3) X.fastidiosa Wells et al. host testing and H. vitripennis transmission studies: Needle inoculation of cover crop plants showed that X. fastidiosa successfully infected and replicated in buckwheat, vetch, sweet alyssum [Lobularia maritima (L.) Desv.] and coriander (Coriandrum sativum L.), plants that were assessed here or elsewhere as nectar producing cover crops for use in vineyards. H. vitripennis successfully transmitted X. fastidiosa between buckwheat and grapevine in the greenhouse and field. H. vitripennis successfully transmitted X. fastidiosa from grapevine to vetch in the field, while transmission studies investigating movement from vetch to grapevine in the greenhouse were inconclusive.

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