- Author: Houston Wilson
Nymphs of Virginia creeper leafhopper (VCLH) and Western grape leafhopper (WGLH) are present and continue to emerge at monitoring sites in Mendocino and Lake Counties (Fig. 1). Peak nymph emergence appears to have past, although we are still seeing some fresh, early instar nymphs.
Nymph emergence in Mendocino County is further along than in Lake County. In Mendocino Co. 57-100% of eggs show signs of emergence whereas in Lake Co. 35-75% of eggs show signs of emergence (Fig. 2).
Sprays were applied for leafhoppers at the Hopland, Ukiah/Talmage, Big Valley 2 and Red Hills 2 sites. Black arrows in Fig. 1 indicate approximate spray date. You'll notice a decline in nymph densities following the sprays at most sites.
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.
We are pausing 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 again.