Vine mealybug (VMB) likes living in Kern County, Calif., vineyards better than it does in many other areas of the state. It sticks around longer in the growing season in the southern San Joaquin Valley county than elsewhere.
For example, when the Flame Seedless table grape season is winding down in late summer, vine mealybugs retreat into the soil to infest another season. At the same time, they are marching up from the soil to crawl on cordons, infesting late-season Crimson Seedless table grapes and rendering them unmarketable.
Vine mealybugs act different in Kern County than they do just one county away in Fresno County, according to David Haviland, University of California IPM advisor for the county.
They pose a longer season challenge to control the pest that has quickly become California grape growers’ public enemy No. 1. It can quickly ruin wine, raisin and table grapes ripe for harvest with a heavy coating of honeydew.
Haviland told an early season gathering of grape growers and pest control advisors in Selma, Calif., that it takes only about five years for vine mealybug to become permanent residents of a vineyard and almost impossible to evict.
It has become such a unique problem in Kern and Tulare county table grape vineyards that a local pest control district made up of growers is funding research to refine a control strategy specific to the region, which is a major table grape producing area. Table grapes can tolerate zero VMB honeydew.
“There are five to seven generations per season in Kern County,” says the UC advisor. “We are taking what Walt Bentley (UC IPM regional advisor) and others have done, and looking at product timing and efficacy in Kern County.”
Vine mealybug have accounted for losses as high as 300 21-pound boxes per acre at harvest in Kern. This represents a third or more of expected yields.
Compounding the problem is the use of common practice of girdling vines at veraison (color break or berry softening) to maintain carbohydrate levels in the upper part of the vine to enhance fruit color and maturation. Girdling is also used early to increase fruit set.
Vine mealybug survive on the roots below ground and move up the vine to damage fruit. Girdling drives the vine mealybug into the canopy to damage bunches with honeydew, rendering the grapes unmarketable.
The wide array of table grape varieties now grown, including many popular late-season types, makes it difficult to design an across-the-board strategy for all table grapes during a very long season that starts in early July and can extend well into November.
Haviland said at the grower/PCA meeting that different varieties and soil types have significant impact on VMB movement and control methods. This can happen to growers with different varieties in the same soil types.
The IPM advisor researched a wide array of products and strategies to keep VMB at bay. Here is what he recommends:
• Lorsban as a delayed dormant or post harvest treatment.
• Applaud use best in May.
• Movento use is flexible, but it seems to have higher efficacy earlier.
• Venom. Not sure what it fits. More field research needed.
• Clutch is best used in May. It has no pre-harvest interval.
• Lannate and Assail are both effective close to harvest.
Movento, according to Haviland, does not have a Maximum Residue Level (MRL) established if the grapes are to be exported. However, Haviland noted that Movento used post harvest does impact MRL. Movento, he says, has proven to be a “phenomenal” post harvest treatment for VMB and an alternative to Lorsban.
Many of these products are used as systemics to reach the VMB where it is normally found in the bark and on the roots.
“The thinking is soil is good and foliar not so good.” However, he said Clutch insecticide proved very effective as a foliar just as it did as a systemic product. This is good news for table grape growers relegated to flood irrigation. Most of the systemic applications are made through drip irrigation systems.