Potato leafhopper control in winegrapes
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Potato leafhoppers (Empoasca fabae) can cause significant injury to winegrape vineyards, causing leaf cupping, reduced shoot growth and leaf yellowing. These symptoms are most evident in sensitive cultivars, which react to the saliva and cell disruption caused during feeding. The most sensitive cultivars are white vinifera (such as Pinot Gris and Chardonnay), although some hybrids (e.g. Cayuga White) are also quite sensitive to this insect. The injury can delay the establishment of young vineyards and can compromise the vine’s ability to grow a large canopy that is needed to ripen fruit.
Potato leafhoppers arrive in Michigan on southerly winds each spring, although their timing and abundance vary greatly between years. A small number of leafhoppers can cause a sensitive response in vines, resulting in a low threshold for this insect in vineyards of sensitive varieties. Research at MSU by Marcel Lenz and Stan Howell on potted Pinot gris grapevines has shown that as few as one potato leafhopper nymph per leaf is sufficient to cause the typical symptoms and measurable reductions in vine growth. However, these studies also suggest that vines can recover from damage if the insects are controlled. We are currently working with MSU’s Paolo Sabbatini to examine the response of vines with varying levels of resistance and different crop loads.
These insects also prefer to feed on the youngest tissues of grape shoots, so they tend to move to newly-expanded foliage. This creates a challenge for vineyard managers in the spring because if a foliar spray has been applied, the rapid shoot growth at this time can mean that new (unprotected) leaves are present within days of an insecticide spray. Often this leads to repeated application of insecticides to maintain protection of the vines, particularly in years when potato leafhopper populations are high or when storm fronts bring repeated infestations to Michigan.
Scouting for leafhoppers
In vineyards sensitive to this pest, early detection is the key to maintaining protection against injury. Weekly scouting should be done through the spring, with more frequent spot checks immediately after rain storms from the south. Potato leafhoppers live on the undersides of leaves and on stems, and move sideways when disturbed. They are bright green and about one-eighth of an inch long. Shaking the foliage of a vine can be used to see if any adult potato leafhoppers are present (they will fly off the vine), but this will not help in detecting the nymphs, which cannot fly. Adult potato leafhoppers arrive first and lay eggs in the leaves, and the eggs hatch into nymphs in early-mid June. Both nymphs and adults can cause vines to exhibit leaf injury, cupping, and shoot stunting, so it is important to count both stages.
Cultural control of potato leafhoppers
Host plant resistance is the main approach that can minimize pest pressure from potato leafhoppers. Vineyards of juice grapes or thick-leaves hybrid varieties tend to have minimal concerns with this insect.
Chemical control of potato leafhoppers
Foliar applications. Application of an effective insecticide to the foliage can quickly stop potato leafhoppers from feeding on the vines. Grape growers currently have a number of effective broad-spectrum insecticide options available, including Sevin, Lannate, Brigade, Sevin, Danitol, Capture, Baythroid and Imidan, which will provide a week or more of protection on the treated foliage. Although they are all active on leafhoppers, the performance of all of these insecticides is reduced by leafhoppers moving to untreated parts of the vine that have grown since the spray was applied. This means that another application may be needed to control potato leafhoppers that move into the vineyard after the earlier spray. To address this problem, growers now have a number of systemic neonicotinoid insecticides that have valuable properties for potato leafhopper control. These provide long residual control because they are absorbed into the foliage after spraying, move within the plant to improve the chance of controlling the leafhoppers, and this makes them much less sensitive to being washed off. Members of this class of insecticides now registered for use in vineyards include Provado, Assail, Actara, Clutch, and the recently-registered Scorpion.
Soil-applied applications. Systemic insecticides provide unique tools for growers because once the insecticide is in the vine; it should provide a long duration of protection against insects feeding on the leaves, stems and shoots of grapevines. This group includes rose chafers, Japanese beetles, leafhoppers, scale and mealybugs. Once the insecticide is absorbed by the roots, it moves in the transpiration stream to the foliage. Insects feeding on the vines would then receive a dose of the insecticide, causing either repellency or death. Potential benefits of this approach to insect control include: longer duration of residual control against foliar pests, protection of insecticide from wash-off, control of multiple pest types with one application, minimal worker exposure to pesticide residues and reduced toxicity to natural enemies.
To get the insecticide into the plant, the soluble insecticide is typically delivered through a drip irrigation system. This is preferable to banding under vines followed by irrigation or rain, as the product moves to the root system more effectively. Our recent research supported this, as we saw high activity only on vines trained to drip, but not in vineyards where the applications were made to the weed-free strip before a rain. There are currently a number of soil-applied insecticides labeled for use in vineyards for systemic control of insect pests, including Venom, Admire Pro and Platinum.
Organic options. Although we have not conducted replicated trials, organic growers have reported activity of 1 percent Stylet Oil against potato leafhoppers. This product can cause temporary inhibition of photosynthesis, so it should be used with caution. Another organic option expected to provide control for a few days is the pyrethrum insecticide Pyganic. Neem containing insecticides such as Azadirect and Neemix are also registered for organic producers.