Sharpshooter Always a Concern

by Val Whitmyre, Master Gardener

At a recent Master Gardener meeting, Napa County agriculture commissioner Dave Whitmer was the featured speaker. He delivered a sobering, but optimistic, message.

Whitmer spoke of how the early Indians had talked together about preserving the beauty and health of their land for seven generations out. They couldn’t have imagined the need for certified organic vegetables or guaranteed free-range chicken. They had no notion of pollution, either, just the contentment of cooking the evening meal under the stars.

As Whitmer spoke, my mind fast forwarded to the present and images of polluted waterways, paved-over farms, chemical pesticides and herbicides and supermarkets full of produce from Chile.

In the early 1990s, I remember seeing ripped-out vineyards where, only a week before, had been a seemingly healthy expanse of green foliage. This devastation, caused by a miniscule root-louse, phylloxera, had infected several vineyards, prompting drastic action to prevent further infection.

There is no turning back to simpler times. Napa Valley has developed into a tourist destination because of our wines, and we have consequently become a mono-crop valley. So we have had to develop solutions to guard against other diseases and pests. We must be vigilant in monitoring and inspecting to keep predators out of our county.

Nature always has another challenge for us. One worry for our grape growers is the glassy-winged sharpshooter, a big, ugly leafhopper. As large as a dime, it has the unpleasant habit of sucking fluid from plant stems and excreting a white liquid so drippy that some liken it to rain.

The sharpshooter’s sucking may not even harm the plant seriously, but as the insect moves from one plant to the next, it spreads the bacteria that cause Pierce’s disease. As these bacteria multiply, they clog the plant’s water-conducting tissue, which can compromise or kill a grapevine. The sharpshooter flies fast and far and could quickly infect a whole vineyard or even a whole county.

This pest lays its eggs on the underside of leaves. Its hosts include grapevines, crape myrtle, sumac, oleander, almonds, oaks, hydrangeas and stone fruit. It particularly likes young grape leaves. Symptoms of Pierce’s disease include leaf wilt, leaf burn or browning, drying or premature leaf drop.

We can help control this devastating insect by regularly inspecting our trees and vines. We can remove suspect plants from our property. To keep the pest out of our county, buy from local nurseries. Buying plants online isn’t buying locally, nor is shopping in adjacent counties.

 Look for a certificate of compliance at your local nursery, which indicates that the nursery is inspecting incoming plants. If you think you have spotted this sharpshooter, call 866-BUG-SPOT or visit bugspot.org to learn how to report the sighting.

The European grapevine moth is a relative newcomer here. By the time it was first spotted in Napa Valley in September 2009, it had severely damaged an entire vineyard. Since then, surrounding counties have reported sightings, too. Experts say the pest came here from Europe via Chile, possibly on fruit or vineyard equipment. It assumes the color of whatever it eats, so it is difficult to spot. It lays its eggs in grapevine flowers and leaf buds. For control, growers are relying on sticky pheromone traps to lure male moths and prevent them from mating. Some are removing host plants, such as crape myrtle, photinia, pittosporum and oleander. The moths also feed on olives, blackberries, cherries, nectarines and pomegranates.

If you have a grapevine and don’t use the grapes, remove all the flowers and developing fruit. Put them in your yard-waste bin and close the lid.

“We are doing all we can, working with our state and federal partners, to implement a plan to combat this pest in Napa County,” says commissioner Whitmer.  He likes to quote T. S.  Eliot: “It is not necessarily those lands which are the most fertile or most favored in climate that seem to me the happiest, but those in which a long stroke of adaptation between man and his environment has brought out the best qualities of both.”

Garden Tour: Save Sunday, May 15, for “Down the Garden Path,” the Napa County Master Gardeners’ garden tour. The tour will showcase seven unique upvalley gardens owned and maintained by local Master Gardeners. For tickets and more information, visit   http://cenapa.ucdavis.edu.

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