Greenhouse Evaluation of Two Different Formulations of Azadirachtin on Egg Mortality of Virginia Creeper Leafhopper, 2016 Open Access

The Virginia creeper leafhopper (VCLH) is an important pest of grape in North America. VCLH feeding on the mesophyll of grape leaves leads to leaf stippling which can reduce vine productivity and ultimately impact fruit yield and quality. Large populations of VCLH adults in the fall can also be a nuisance to workers manually harvesting grapes. Azadirachtin is a recommended product for use against VCLH nymphs. Early season applications (May–Jun) are best since VCLH generations and life-stages are still relatively distinct. Spray timing can become more problematic later in the growing season (Jul-Sept) when overlapping VCLH generations lead to the simultaneous presence of eggs, nymphs and adults in the vineyard. If late season chemical controls are required, then chemical controls that are effective against multiple life stages of VCLH may be more effective. This study was designed to test the impact of two different formulations of azadirachtin (DeBug Turbo and DeBug Trés) on egg mortality of VCLH.

This trial was conducted at the UC Berkeley Oxford Tract greenhouse facilities from 6 Jul to 1 Aug 2016. An RCB design was used with six replicates of five different spray treatments (Table 1). The experimental area consisted of a large greenhouse bench that was divided into six blocks. Each block consisted of five potted grape vines that were each randomly assigned to one of the five possible spray treatments. All spray treatment rates (Table 1) are per acre at a finished spray volume of 60 gpa. Spray treatments were applied to individual potted grape vines using a 48-fl oz hand-held pressure sprayer. On 6 Jul, 30 potted grape vines with six fully expanded, mature leaves were each inoculated with approximately 70 adult VCLH (2 vials with 37.2 ±1.9 adults each, 1:0.7 F:M) that were collected from a vineyard in Mendocino County. After 72 h of oviposition, the adults were removed from the potted vines with a D-Vac type insect vacuum. Leaves were also visually inspected to ensure no adult VCLH remained on any of the vines. Potted vines were then sprayed with their respective treatments until the leaf surface was thoroughly wetted without excessive run-off. Vines were held in cages in a greenhouse (73.9 ±0.1 °F, 55.5 ±0.2% RH) for 23 days to allow for VCLH egg development and nymph emergence. Leaves were then removed and egg mortality was evaluated using a dissecting microscope.

Treatment effect on proportion egg mortality was assessed with logistic regression using a generalized linear mixed model with binomial distribution. Means were separated with post hoc Tukey contrasts contingent on significant c² (P < 0.05) value. All of the formulations evaluated were effective at increasing egg mortality relative to the water check (Table 1). DeBug Turbo generally achieved greater egg mortality than DeBug Trés and the highest egg mortality was observed where the highest concentration of DeBug Turbo was used.

This research was supported by industry gifts of pesticides and research funding.

Author notes