By Houston Wilson
Egg deposition by both Virginia creeper leafhopper (VCLH) and western grape leafhopper (WGLH) continues to take place in both counties (Fig. 1). VCLH egg deposition is starting to level off in Mendocino County (Fig. 1B) and the VCLH nymphs are beginning to emerge there (Fig. 2B). No nymphs of either species have been observed yet in Lake County. Note that in Fig. 2 "Early Instar" are early stage nymphs (1st - 2nd instar) that we can not yet differentiate between VCLH and WGLH.
Nymph emergence will continue to increase in the coming weeks, so now is the time to start thinking about 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 the emergence of 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 May 19 we released another batch of Anagrus daanei in a Lake County vineyard located in the Big Valley area.