Emergence of Virginia creeper leafhopper (VCLH) and Western grape leafhopper (WGLH) nymphs continues to increase in both counties (Fig. 1). Egg deposition has mostly ceased, although there is still some activity in the Red Hills area of Lake County (graphs not shown). Nymph emergence is further along in Mendocino County, where we are seeing 50-68% of eggs already emerged (Fig. 2B). In Lake County, 3-50% of leafhopper eggs have emerged (Fig. 2A).

Nymph emergence will continue to increase in the coming weeks, so now is the time to be monitoring nymph populations in your vineyard. Leafhopper nymph identification guidelines are available here (video) and here (text version).

Due to the lack of biological control, effective early-season control of VCLH is critical. Based on monitoring, if control measures are needed, the optimum application period would be when the majority of the population is still in the younger nymphal stages before they molt into adults. This is especially important if you plan to spray with an oil. Depending on population levels at your site, a follow-up application may be required to impact nymphs that emerge after the spray. Consult your PCA for materials, rates and timing.

Last Friday June 2 we released another batch of Anagrus daanei in a Lake County vineyard located in the Big Valley area. We will pause the parasitoid release program for a few weeks since egg deposition is no longer taking place. We will resume the releases once the current nymphs begin to molt into adults and we start to see fresh eggs on the grape leaves.