BIG VALLEY – The Lake County Department of Agriculture is reporting the detection of a serious grape pest, the Vine Mealybug (VMB), in the Big Valley area.
In late December 2006, the California Department of Food and Agriculture diagnostic laboratory sent confirmation to the county's Agriculture Department that six male VMBs had been caught in special traps baited with a chemical attractant specific for mealybug males.
The Lake County Agriculture Department has been running a VMB trapping program in vineyards throughout the county since 2004, and this is the only location where VMB has been found, first in 2004 and now in 2006.
Following the notification of the 2006 find, as in 2004, the grower took the immediate action of applying an insecticide to knock down any population of the mealybug that might be above ground level.
Other areas of the state that are infested with VMB report that this strategy appears to control small, pioneer populations of this insect, affording many years of reduced risk of possible spread.
The find of only six males at the very end of the 2006 trapping season is typical of an incipient infestation, possibly limited in size. It is necessary to locate the affected vines and send females for diagnostic analysis to definitively confirm the presence of an infestation.
To date, no female VMBs have been found in Lake County. The VMB goes below ground during the dormant season and will not re-emerge until early summer.
The Department of Agriculture plans on doing field surveys this year to see if female VMB is present in the vineyard in question.
The Vine Mealybug represents a serious pest of vineyards wherever it has become established. It is very difficult to eradicate once it gains a foothold in a vineyard, as a certain percentage of the population is always below ground.
The VMB reproduces rapidly and produces copious amounts of "honeydew," a sticky, sugar-laden substance that promotes mold and bacterial growth and encourages ants to protect the mealybugs, as they collect some of this substance for food. The mold and bacteria will damage fruit clusters to the point of non-marketability.
As with any mealybug, they feed on the vascular portions of the vine, so they also sap the vigor of the vine over time and can cause a significant reduction in vine health and production.
Recent data also indicates that the VMB can vector a serious grape disease called Fan Leaf Virus, which adds more incentive for growers to detect this pest and guard against its introduction.
Early detection of this pest is critical to reducing its spread and possibly eradicating it at the find site. To that end, the Lake County Department of Agriculture launched a two-pronged detection effort for this pest starting in 2004.
First, the department runs roughly 100 VMB traps countywide in all the major grape growing regions, with traps spread out at University of California recommended trap densities.
The second, and equally important, aspect of the detection program, is the VMB traps that individual growers put in their vineyards. The Department of Agriculture supplies the traps and pheromone free of charge as well as the expertise to scan the old traps for possible VMB.
This grower participation represents a critical link in early detection of this pest, which is well established in Napa and Sonoma counties.
VMB trapping should be a regular part of every vineyard's pest management program, as this pest is "knocking at our door" and will be costly and require more pesticide applications for any vineyard which becomes infested.
If you have any questions or would like more information about the Vine Mealybug, you can visit the web page of the Lake County UCCE office at celake.ucdavis.edu and click on the "Viticulture and Enology" icon, or you can call the Lake County Department of Agriculture at 263-0217.
Chuck Morse is Lake County's deputy agriculture commissioner.
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