Pest description and crop damage This scale overwinters on grape canes as an immature brownish to black scale of about 0.06 to 0.14 inches long and has a flat and oval outline. Scales attain a maximum length of about 0.25 inches during spring. The conspicuous, cottony egg sac of the mature form is two to three times the length of the scale body. The insect feeds on foliage, reduces the vigor of the plant, and causes twig dieback. Feeding scales produce honeydew, which becomes a food source for ants and a substrate for sooty mold. Scout for noticeable presence of ants, as this may be the first sign that the scale is present on a vine.
Biology and life history Each female lays about 3,000 eggs. The egg sac remains for some time after the female has died and crawlers have dispersed to the undersides of leaves. Scales reach maturity in June, and crawlers appear in July and August. This pest has not been common in Oregon vineyards. Caution is to be taken with scale insects as they may vector certain grapevine viruses, such as grapevine leafroll virus.
Although biological controls of cottony maple scale have not been studied, scale insects generally are preyed upon heavily by parasitic wasps.
Since much of the vine is removed at pruning, it may be unnecessary to apply control measures unless the scale is infesting the main trunk or cordons.
Management-chemical control: HOME USE
- horticultural oils-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- buprofezin (Applaud) at 0.53 lb ai/a. PHI 7 days. Do not exceed 1.06 lb ai/a per season. Allow at least 14 days between applications. Apply by ground using 50 to 200 gal/a water, depending on the size of the grape plants. Use of a higher volume of water will ensure better coverage, especially under adverse conditions, such as hot, dry weather and/or a dense canopy. Do not exceed two applications per season. Although cottony grape scale insect is not specifically listed on the label for grapes, it is an effective and legal use. Group 16 insecticide.
- horticultural oil (several brands)-Consult label for rate. Apply oil at a spray volume of 200 to 300 gal/a. Apply in late March or early April while vines are still dormant; do not apply oil after budbreak. Some formulations are OMRI-listed for organic use.
- imidacloprid (Admire Pro and other brands)
- Soil application at 0.25 to 0.5 lb ai/a. PHI 30 days. Apply in one or two drip irrigations between budbreak and pea size stage of berry development. Consult label for restrictions. Do not apply more than 0.5 lb ai/a per year. Group 4A insecticide.
- Foliar application at 0.036 to 0.05 lb ai/a. PHI 0 days. Although scale insect is not listed under foliar applications for grape, it is a legal use and should be helpful in controlling scale crawlers. Do not exceed 0.1 lb ai/a per year. Allow 14 days between applications. Group 4A insecticide.