Photo courtesy of the California
Department of Agriculture

By Vicky Boyd
Editor


Bordered by Sanger, Fowler, Selma, Kingsburg and Reedley, California’s Golden Triangle is blessed with rich soil that produces world-renowned fruit.


Now about 100 square miles within the triangle also fall under the European grapevine moth quarantine.


For growers, such as Keith Nilmeier, who farm within the quarantine area south of Fresno, the added restrictions mean uncertainty and additional costs.


“The ramifications are not just what it’s costing us but the loss of the foreign markets,” says Nilmeier, who has 300 acres of stone fruit, grapes and citrus south of Fresno. “When we start loosing our markets, that hurts. That’s what really hurts.”

He was referring to restrictions foreign trading partners have placed on fruit originating from the quarantined area.

Australia, New Zealand, Chile, Peru and Canada already have notified the U.S. Department of Agriculture that they will not accept fruit from the quarantine area, says Helene Wright, U.SDA state plant health director in Sacramento. Mexican officials have gone further and say they will not accept any fruit from Fresno County.







Photo by Monica Cooper,
University of California Cooperative Extension

Life stages of the pest


The cause for everyone’s concern is a rather non-descript 3/8-inch brown moth that’s native to the Mediterranean.


Known scientifically as Lobesia botrana, the European grapevine moth belongs to the tortrix family, which also includes Oriental fruit moth and light brown apple moth.


In California, grapes are the main host, says Walt Bentley, a University of California Extension entomologist based at the Kearney Agriculture Center near Parlier.


Female moths lay eggs on grape clusters or berries. In heavy infestations, such as in Napa County, females also will lay eggs on olive flowers, although that is not a preferred host, he says.

In the spring when temperatures are cooler, the eggs take seven to 11 days to hatch. During the summer, they take only three to six days.

European grapevine moth larvae are about 1/4-inch long and about half the size of a mature omnivorous leafroller.


Both also have white spots on the abdomen sections.

What differentiates the two is the European grapevine moth larvae have a small, darkish shield after the first set of legs.

For more information on how to identify the pest, including color images, visit http://www.ipm.ucdavis.edu.


Treatments easily control pest


The European grapevine moth larvae feed on the berries, rendering them unmarketable. The feeding also provides an entry way for secondary invaders, such as Botrytis, to enter. One berry may host multiple larvae.


“They’re able to survive only on the berries—they don’t live on leaves,” Bentley says.


Scientific literature also lists several other hosts for the pest, including stone fruit, pomegranates, kiwi fruit, gooseberries, blackberries and persimmons.


But Bentley emphasized that they are very poor hosts.


“That doesn’t make a difference to some of our trading partners, but it does make a difference in our ability to eradicate it,” Bentley says.


The moth most likely has three generations in the Central Valley, he says. Insects overwinter as pupae under bark or other protected places and emerge as adult moths in late April to early May. Females lay eggs from late April through May.


The second generation lays eggs during July, and the third during September.


Larvae are easily controlled with several registered products, such as Intrepid and Altacor, he says. Both of those products are ovicides, meaning they’ll kill eggs. They also act on the larvae.


In addition, they are very targeted and do not harm beneficials, so they shouldn’t disrupt biological control, Bentley says.


Carol Hafner, Fresno County agriculture commissioner, has urged all grape growers within the quarantine to treat for the pest, adding, “I’m confident we can eradicate this.”


Stephen Vasquez, a UC farm adviser in Fresno County, will alert growers when the optimum spray time is for the second- and third-generation larvae.


For a complete list of registered products, visit http://cefresno.ucdavis.edu.


Additional sprays may be needed


Terry Schneider, who describes himself as a small grower with 20 acres of Thompson seedless for crushing, says he’s still trying to figure out how the requirements will affect him. His farm is in the northern part of the quarantine.


“My problem is I don’t necessarily have to spray. But my neighbor with 100 acres doesn’t do anything. If that is going to be a host vineyard, I don’t want them in mine.”


He does his own spraying, but says he doesn’t know how much the material will cost him for the additional treatments.


Many stone fruit growers already use one of the registed products or a similar one as a mid-May spray to control peach twig borer, says Sara Savary, a pest control adviser with Crop Care Associates in Fresno. So that treatment should control any European grapevine moths present, too.


Where she sees additional sprays are with the clients she serves who grow raisins.


“They’re usually not spraying for worms until the next OLR (omnivorous leaf roller) hatch until the beginning of July,” she says. “By then, I usually know if I have a problem. My raisin guys will not be happy about another worm spray.”

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