Farm Progress

Some work in the vineyard before bud break can reduce populations of leafhoppers.

Tim Hearden, Western Farm Press

September 12, 2018

3 Min Read
The Western grape leafhopper is one of several species of leafhoppers that are common pests in California vineyards.University of California Regents

Some attention to detail in the winter and spring can help grape growers avoid having to use chemical treatments for leafhoppers, according to the University of California Statewide Integrated Pest Management Program.

Although leafhoppers infest most vineyards in the state, they may not require chemical treatment because vines can tolerate fairly high populations without harm, and their natural enemies may be able to contain them, the university notes.

But leafhopper populations in the coastal regions and Central Valley may occasionally reach damaging levels and require treatment. To avoid this, growers can take several measures, such as removing basal leaves or lateral shoots during and just after berry set, as they would for Botrytis bunch rot management. This can reduce leafhopper populations during the growing season by 30 percent to 50 percent.

ABOUT LEAFHOPPERS

There are actually several types of leafhoppers that infest grapes grown for wine, raisin, and fresh, the UC IPM explains in pest management guidelines on its website.

The variegated leafhopper is the most common pest of grapes from southern California north to San Joaquin County, and is also found in Napa County. The grape leafhopper resides in inland valleys north of the Tehachapi Mountains, and the Virginia creeper leafhopper has been occasionally detected in Northern California.

Leafhoppers overwinter as adults and are found in the spring in basal grape leaves and weeds. Nymphs and adults remove the contents of leaf cells, leaving behind empty cells that appear as pale yellow spots or stippling.

If densities are really high, loss of leaf efficiency and leaf drop can result in fruit sunburn and may delay fruit ripening, especially in young vines. Moreover, the accumulation of small droplets of excrement on berries and growth of sooty mold cause berry spotting that is a concern in table grapes, the scientists say. Adult leafhoppers are also a nuisance to pickers during harvest when populations are high.

MANAGING LEAFHOPPERS

Many natural enemies help to control leafhopper populations, the researchers note. Egg parasites, Anagrus erythroneurae and A. daanel, may be more abundant in vineyards that are adjacent to prune, plum, and almond orchards, and near riparian areas where other leafhoppers reside.

Unfortunately, these parasites are not as effective at controlling variegated leafhopper eggs as they are on those of the grape leafhopper, the scientists say. The eggs of Virginia creeper leafhopper are parasitized by two enemies, A. tretiakovae and A. daanel, in Washington state and British Columbia, and researchers are studying whether they’re having an effect on the pests in California.

General predators of leafhoppers include spiders, green lacewings, minute pirate bugs, lady beetles, black hunter thrips, and predaceous mites. Many growers have experimented with releases of lacewings for leafhoppers.

Among cultural controls, removing basal leaves or lateral shoots during berry set and the two-week period just afterward, before adult leafhoppers emerge, can achieve significant reductions in leafhopper populations. In fact, this coupled with Anagrus activity may preclude the need for insecticide treatments, according to UC IPM.

Growers should time leaf removal to coincide with first-generation nymphal development up to and including the fifth instar, or stage of the insects between molts, but just before adults are present. Preventing overly vigorous vine growth can also suppress leafhoppers, but growers in warmer areas are cautioned not to remove so many leaves that it leads to sunburned fruit.

If the vineyard is accessible before budbreak, removing weeds in vineyards and surrounding areas before vines start to grow in the spring will also reduce adult leafhopper populations.

Population thresholds for determining if chemical treatment is necessary vary according to the pests’ generation and species; whether grapes are being grown for table, wine, or raisin use; canopy size; region; and degree of parasitization.

For detailed advice, consult the UC IPM’s management guidelines at https://bit.ly/2CycT0M

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