University of California Cooperative Extension North Coast IPM Advisor Lucia Varela proved to be a bit of a prophet earlier this spring at the annual Sonoma County grape day in Santa Rosa, Calif.
In bringing North Coast grape growers up to speed on the latest exotic pest to penetrate California's borders, the light brown apple moth (LBAM), she said the pest prefers cooler climates like the North Coast.
Sure enough, California Department of Food and Agriculture inspectors trapped a male LBAM moth in Sonoma, Calif., just eight days after Varela spoke at grape day. Experts confirmed the find, a first for Sonoma County, about two weeks later.
About 300 pheromone traps are now deployed within a nine-square mile area near Sonoma.
If more moths are trapped, the area could be declared infested and face a fruit movement quarantine to prevent the LBAM from spreading.
Varela told grape growers and PCAs that the bad news is LBAM is in the state. The good news is that it is a pest similar to other leafroller pests, orange tortrix and omnivorous leaf roller (OLR) in the state. Therefore, the same parasites and pest control products that control its cousins also control the LBAM.
Unfortunately, it is an exotic pest that is found only in its native Australia and neighboring New Zealand, the United Kingdom and Hawaii.
A quarantine triggered by more finds could severely restrict movement of grapes, strawberries, apples and other fruit from Sonoma County. Already, the moth's presence has prompted Mexico and Canada to impose export regulations on California. The pest feeds on more than 2,000 plants, including more than 250 farm crops.
Agriculture officials first detected LBAM in California about a year ago. Most Bay Area counties are now under apple moth quarantines to halt its spread.
A U.S. Department of Agriculture study reported that if California becomes “generally infested,” the moth could cause $160 million to $640 million annually in crop damage.
The light brown apple moth also attacks a variety of garden plants, plus oaks, Douglas firs, and redwoods.
The federal government has earmarked $75 million this year to eradicate the pest in the state. Key to the efforts are plans for aerial spraying of infested areas with a synthetic moth pheromone designed to disrupt the pest's mating.
The state is planning to spray a mating disruption pheromone product Check-Mate over Berkeley, Oakland and other East Bay communities in August to combat the spread of the moth.
Similar spraying in Monterey and Santa Cruz counties set off a flurry of complaints. Officials say the state received 640 complaints of people feeling ill after spraying occurred in Santa Cruz County last fall.
California officials insist the chemical is safe. But spraying opponents say the state has not adequately investigated health complaints from Central Coast communities where the spray was applied last fall.
Twist ties infused with pheromones that attract and confuse the male moths helped eradicate LBAM in Napa and Los Angeles counties.
Varela told Sonoma County grape day that LBAM does not survive well at high temperatures. It collapses at 100 degrees, she noted. The pest is most damaging when the mean temperature is about 56 degrees and there is moderate rainfall.
A degree-day model used for predicting LBAM development indicates that there will most likely be 2 generations a year in the Central and North Coast areas of California, and 3 or 4 generations a year in the Central Valley and Southern California regions.
It does not go into diapause in winter. It overwinters as larvae, but cold winter temperatures slow larval development.
The moth overwinters as a second to fourth instar larva feeding on herbaceous plants, on the buds of deciduous trees or shrubs, on mummified fruit, and other plant material.
Larvae may survive for up to 2 months in the winter without feeding.
These pheromone traps deployed at the rate of one per five acres are recommended to detect and monitor LBAM populations with at least one in every field, regardless of size.
To detect LBAM eggs and larvae, Varela urged growers and PCAs to examine leaves closely. Look for the characteristic webbing on grapevine shoots, said Varela.
This webbing can be seen at the mid-rib vein on the underside of leaves and between leaves. When there is fruit on the vine, examine clusters of fruit by separating and looking between the fruit. She suggested removing infested clusters.
The leafroller pest can cause Botrytis bunch rot by feeding on berries. Look for larvae in fruit mummies.
LBAM feeds from within the sheltering nest it constructs. Foliar feeding is usually considered minor in fruit crops. On fruit crops the primary concern is fruit damage. Larvae remove the outermost layers of the fruit surface as they feed. Superficial feeding injuries to the fruit are typically caused by later immature stages.
Minor feeding damage can take the form of pinpricks or “stings” on the fruit surface. In grapes, larvae can cause extensive loss of flowers or newly set berries in the spring. Later in the season, grapes can be severely damaged by larvae feeding among the berries, allowing mold organisms, Botrytis, and bunch rot to get started. More details about the latest invasive species to find California are on the UC Statewide IPM Program Web site.