Virginia creeper leafhopper (Erythroneura ziczac)
Western grape leafhopper (Erythroneura elegantula)
Pest description and crop damage Adult western grape leafhoppers (WGLH) and Virginia creeper leafhoppers (VCLH) are about 0.12 inch long and are pale yellow with reddish and dark brown markings. VCLH can be distinguished from WGLH by red spots on the back behind the eyes. The short life cycle of both leafhopper species enables them to increase populations rapidly.
The eggs of both species are bean-shaped, 0.03 inch long, and laid mostly on the undersides of leaves, just under the epidermis. The eggs of WGLH are laid singly, but eggs of VCLH more often are laid in rows of two to nine. Newly hatched nymphs of both species are white. After 1 day, red spots appear on the back of VCLH nymphs.
Leafhopper adults and nymphs pierce leaf cells and suck out the contents. Each feeding puncture leaves a white spot. As injury increases, photosynthetic activity declines; heavily damaged leaves turn yellow and brown and fall off the vine in severe cases.
Biology and life history Grape leafhoppers overwinter as non-breeding adults in plant debris and leaf litter in protected locations. Adults emerge from overwintering sites in March and feed on annual weeds on the vineyard floor. They move on to grape foliage after budburst, and females begin laying eggs usually in late April. Egg-laying continues for about 6 weeks.
The first generation of nymphs feeds primarily on basal leaves from May to June and produces new generation adults in July. The second generation of nymphs appears later in the month (feeding on younger leaves, including leaves toward the shoot tip and leaves on laterals) and produces the second adult generation in the latter half of August and September. These adults form the overwintering population.
Sampling and thresholds The relationship between leafhopper populations and economic damage to wine and juice grapes is not well understood in the Pacific Northwest, but it is clear that vines can tolerate large populations before suffering economic loss. This is particularly true for spring populations of overwintered adults and first generation nymphs, which confine their feeding activity to the basal six to eight leaves.
The second generation of nymphs moves onto outer canopy leaves. Their numbers should be assessed using leaf counts. An average of more than 20 nymphs per leaf on outer canopy leaves, with no evidence of egg parasitism, is likely to require treatment.
Several generalist insect and mite predators prey on leafhopper adults and nymphs of all stages. Among the most abundant are lacewings, predatory bugs, predatory beetles, and spiders. The most important natural enemies of grape leafhoppers are microscopic parasitic wasps, particularly several different species of Anagrus. Anagrus wasps parasitize leafhopper eggs and can cause up to 100% mortality in August to September. Anagrus wasps cannot overwinter in vineyards, as they require a leafhopper host that overwinters as an egg. Thus, they take some time to recolonize vineyards during spring to summer, particularly when insecticides are being used.
The presence or absence of Anagrus wasps should be assessed before making management decisions. Anagrus is detected easily by observing the eggs leafhoppers: parasitized eggs turn brick-red before the adult wasps emerge. Always regard the presence of Anagrus during the first generation of eggs as a significant mortality factor. Buprofezin (Applaud) is the only insecticide compatible with Anagrus and is recommended.
Increased vine vigor and dense canopies tend to promote leafhopper populations. Maximum vineyard productivity is obtained from moderate vigor vines with less canopy density, which are only moderately attractive to leafhoppers.
Disking or tilling soil to remove weeds and vineyard debris in late winter to early spring can reduce populations of overwintered leafhoppers. If maintaining a vegetative cover in the alleyway (grass, weeds, or cover crop), consider mowing early in the season to reduce adult populations. Waiting until after budbreak to mow or till can result in adults moving to the vine foliage.
Management-chemical control: HOME USE
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- horticultural oils (rates vary with product)-Ensure good coverage of leaf surfaces. Some formulations OMRI-listed for organic use.
- insecticidal soap-Some formulations OMRI-listed for organic use.
- kaolin-Applied as a spray to foliage, stems and fruit it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
- malathion-Spray when nymphs are on undersides of leaves.
- pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- acetamiprid (Assail 30SG) at 0.047 to 0.1 lb ai/a. PHI 3 days. Do not exceed two applications per season (0.2 lb ai/a), and allow at least 14 days between applications. Group 4A insecticide.
- abamectin (Agri-Mek 0.15 EC) at 0.009 to 0.019lb ai/a. Apply with a nonionic surfactant (NIS) for contact knockdown only. PHI 28 days. Do not exceed two sequential applications or 0.038 lb ai/a per season. Group 6 insecticide; restricted use.
- bifenthrin (Brigade and other brands) at 0.05 to 0.10 lb ai/a. Do not apply more than 0.10 lb ai/a per season. PHI 30 days. Group 3A insecticide. Restricted use pesticide.
- buprofezin (Applaud) at 0.40 to 0.53 lb ai/a. PHI 7 days. Use 50 to 200 gal/a water. Do not exceed 1.05 lb ai/a per season. Allow at least 14 days between applications. Group 16 insecticide.
- Chromobacterium subtsugae strain PRAA4 (Grandevo) at 2 to 3 lb product per acre. PHI 0 days. OMRI-listed for organic use.
- fenoproprathin (Danitol 2.4EC) at 0.1 to 0.2 lb ai/a. Do not apply more than 0.8 lb ai/a per season, and do not apply more than two times per season for resistance management. PHI 21 days. Group 3A insecticide. Restricted use pesticide.
- 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. Do not exceed 0.1 lb ai/a per year. Allow 14 days between applications. Group 4A insecticide.
- insecticidal soap (M-Pede and other brands) at 2% solution; Consult label for rates. PHI 0 days. Do not mix with sulfur. Some formulations are OMRI-listed for organic use.
- kaolin clay (Surround WP) at 25 to 50 lb product per acre. The preferred rate is 25 lb of product in 50 gal water/a. Suppression only; supplemental controls may be needed for complete control. Apply at least two to three applications at 7- to 14-day intervals. OMRI-listed for organic use.
- stylet oil at 1 to 2 gal of product per 100 gal water/a. Do not apply sulfur within 10 days of applying oil. Do not apply when temperatures are above 90°F (potential tissue burning) or below 50°F (reduced efficacy). Some formulations are OMRI-listed for organic use.
- thiamethoxam + chlorantraniliprole (Voliam Flexi) at 0.155 fl oz of product/a. PHI 14 days. Allow 14 days between applications. Do not apply more than two applications per season (maximum of 0.109 lb ai/a of thiamethoxam or 0.2 lb ai/a of chlorantraniliprole per season). Groups 4A and 28 insecticides.