Ministry of Agriculture
Grape Insect and Mite Pests
(Virginia creeper leafhopper, Erythroneura ziczac Walsh)
(Western grape leafhopper, E. elegantula Osborn)
- Life Cycle and Damage
- Monitoring and Spray Thresholds
- Biological Control
- Cultural and Physical Control
- Chemical Control
Prepared by D. Thomas Lowery, Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland.
Leafhopper photographs courtesy of M. Gardener, Agriculture and Agri-Food Canada.
In addition to the widespread Virginia creeper leafhopper (VCLH), the western grape leafhopper (WGLH) occurs on the east side of the Okanagan Valley from the north end of Penticton south to the U.S. border. The WGLH is more tolerant to insecticides and it is important to determine if it is present in your vineyard. Leafhoppers are often distributed unevenly in vineyards and monitoring will help determine which areas require treatment. Unnecessary sprays reduce numbers of beneficial insects and spiders, resulting in a rapid resurgence in pest numbers and outbreaks of thrips, mites, and mealybugs. Experience has shown that WGLH numbers are low in organic vineyards; damaging populations in conventional vineyards generally result from repeated sprays of insecticides that do not control this species but damage numbers of the egg parasite, Anagrus erythroneurae. Successful control of leafhoppers relies on proper monitoring of numbers throughout the vineyard and the judicious use of insecticides in order to preserve beneficial insects and spiders.
|Western grape leafhopper adult||Virginia creeper leafhopper adult|
|Western grape leafhopper nymph||Virginia creeper leafhopper nymphs|
|Leafhopper feeding damage to leaves||Virginia creeper leafhopper eggs|
Adults of both species are similar in appearance, nearly ½ cm in length with reddish-brown markings on a pale white or yellowish background. Adult WGLH can be distinguished by their pale eyes and irregular reddish-orange markings on a whitish background. VCLH have reddish-brown eyes and a more regular reddish-brown zigzag pattern on the wings. The background body colour is pale yellow to light brownish-yellow, producing an overall darker appearance. Adult leafhoppers are best identified on yellow sticky cards placed in outer vineyard rows during late April and May that can be inspected with the aid of a hand lens or magnifying glass.
Immature stages (nymphs) of WGLH are distinguished by their pale white colour, lack of pigmentation in the eyes, and the presence of one to three pairs of pale indistinct yellow spots on the thoracic segments of larger nymphs. VCLH nymphs have reddish-brown eyes and a pale yellowish body colour. Larger VCLH nymphs develop a pair of dark reddish-brown spots on the first body segment behind the head and a pair of reddish-orange spots on the other two thoracic segments. Nymphs can be identified feeding on the undersides of fully expanded leaves that show signs of feeding damage (stippling).
The biology and life cycles of the two species are similar. There are two generations each year. Adults of both species spend the winter in leaf litter or under plant debris in the vineyard or in nearby vegetation. Adults emerge on warm spring days to feed on a wide variety of plants, moving to grape, Virginia creeper and Boston ivy when the first leaves appear. The overwintered females deposit eggs in the leaf tissue on the undersides of fully expanded leaves during May and June. The small, flattened opaque eggs are deposited side by side, usually in small groups of around two to six for the VCLH and singly for the WGLH. Nymphs of this 1st generation hatch mainly from mid June to the end of July. There are five nymphal stages. Winged adults that appear during July and August lay eggs that develop throughout the fall into overwintering adults. The WGLH develops more slowly than the VCLH and nymphs will occur later into the year. Both adults and nymphs feed by piercing individual leaf cells and sucking out the contents. Light infestations cause leaves to appear stippled due to the death of individual cells. Heavier feeding results in brown, dried leaves that fall prematurely. Some studies have shown that light infestations can actually improve the quality of grapes on vines that are overly vigorous, but excessive feeding reduces the photosynthetic activity of the vines, resulting in delayed maturity, yield losses, and reduced fruit quality. Large infestations deplete carbohydrate stores and weaken the vines. Light coloured varieties can become spotted and unsightly with excrement, which is a particular concern for table grapes. Adult leafhoppers are also an annoyance to pickers during harvest. Neither species is known to transmit viruses or other plant diseases.
Overwintered adults usually congregate in higher numbers on the edges of vineyards or in sheltered locations and these areas should receive particular attention in the spring. Leafhoppers also prefer vigorous vines and those that leaf out earliest. Monitoring numbers of adults captured in spring on yellow sticky cards can help determine relative infestation levels, but because some eggs fail to develop and predation rates are variable, these numbers do not correlate well with subsequent nymph counts. It is helpful to note where large numbers of adults occur early in the season, as these areas should be observed more closely later on.
Adults are more tolerant of insecticides and sprays should be targeted against the wingless immature stages. Depending on the location of the vineyard, monitoring of 1st generation nymphs should begin in early to mid June. Monitor populations by counting numbers of nymphs on the lower surfaces of 5-10 leaves in at least 5 locations per block or variety. Select older bottom leaves up to just above the fruiting zone. In order to prevent damage to any vines, sampling should focus on more heavily infested areas. Sample from the north and east sides of rows where more nymphs will be found and focus on the leaf zone showing signs of feeding damage. Infestation levels are based on the average number of nymphs per leaf.
Established grapevines are tolerant of leafhopper damage during the first half of the season when growth is rapid. Because of this, there are no established thresholds for 1st generation nymphs. The threshold of approximately 20-25 nymphs per leaf established for the 2nd generation in late summer can also be used as an approximate threshold for early summer sprays. A higher threshold can be used for 1st generation nymphs if healthy populations of predators are present and a high rate of parasitism is likely. Control of 1st generation nymphs is often more effective as there is less foliage, nymphs are confined to leaves around the fruiting zone, and sprays can be directed in a narrow band to ensure good coverage. It is recommended, therefore, to treat vineyards with a history of heavy leafhopper damage during this time. Soap sprays are much more effective when targeted against 1st generation nymphs when approximately 80% of the eggs have hatched. Egg hatch can only be determined with the aid of a low power microscope, but the presence of mostly small, young nymphs can be used as an approximate measure. Because soaps are not as effective as other insecticides, the threshold for vineyards that are managed organically should be reduced considerably, perhaps to around 5-10 nymphs per leaf.
Second generation nymphs should be monitored beginning in August in a manner similar to that outlined above. Greater attention should be paid to vines in the center of the field, however, as infestations will have spread from field edges and ‘hot spots’ to a larger area of the vineyard. Nymph counts should be collected initially every other week, and then weekly when the time for spraying approaches. For wine grapes, an approximate threshold of 20-25 nymphs/leaf on the more heavily infested leaves can be used as a rough guideline. This is an average value based on counts from several leaves as outlined above. Again, for a particular area of the vineyard, collect at least 5 leaves from 5 areas and calculate the average number of nymphs per leaf. For 2nd generation nymphs, sample leaves from the middle of the canopy above the fruiting zone and from the north or east sides of vines where numbers will be higher. Leafhoppers will be distributed unevenly in a vineyard and it is important to sample thoroughly to determine which areas require treatment. Although the above threshold provides a rough guideline, an acceptable spray threshold should be determined by individual growers based on their past experience and additional factors such as vine vigour and numbers of beneficial insects.
Birds, spiders, predators, parasites, and diseases attack leafhopper eggs, nymphs or adults. A small egg parasite, Anagrus daanei, helps control VCLH in some vineyards where parasitism rates approach 100% late in the season. A different parasite, A. erythroneurae, parasitizes eggs of the WGLH and is largely responsible for the control of this pest. A. erythroneurae overwinters in eggs of the rose leafhopper on wild and domestic roses, apple, blackberry and plum. In early spring this parasite utilizes eggs of a leafhopper found on a wide range of mints, including catnip and catmint. Most vineyards have large numbers of A. erythroneura and outbreaks of WGLH are largely associated with sprays of insecticides that do not control this leafhopper but are toxic to the parasite. Excessive rates or unnecessary sprays of insecticides will also reduce numbers of other beneficial insects and spiders.
Leafhoppers prefer excessively vigorous plants and vines should be irrigated and fertilized to maintain moderate growth best suited to the production of high quality wine grapes. The use of yellow sticky tape applied below the cordon in spring can be an economical way to manage leafhoppers in some vineyards. Although costly, this method helps preserve beneficial insects and reduces or eliminates the need for additional insecticides later in the season. The use of sticky tape is likely not cost effective for large areas but it can be a useful method where infestations are confined to small areas or to the edges of vineyards.
A recently completed study demonstrated that removal of basal leaves early in the season (mid to late June) when most eggs of the 1st generation have been laid effectively reduced numbers of leafhoppers and the incidence of bunch rots. No significant differences were noted in fruit quality other than a slight reduction in yield and berry size, but it is recommended that growers first assess the effectiveness of early leaf removal on only a few vines of each variety. Removal of leaves around the fruiting zone at any time of the season might not be suitable for stressed vines or on sites with intense heat and light that might lead to sunburn. This practice is labour intensive, but growers often remove these leaves later in the season in order to improve grape quality. Removing basal leaves too early will force leaf-hoppers to deposit their eggs higher up the vine and might inhibit bud initiation required for the following year.
Some insecticides registered for the control of leafhoppers are ineffective for the WGLH and it is important to determine if this species is present in your vineyard. If only the VCLH is present, natural enemies should be preserved by applying the lowest effective rate only to areas where the pest has exceeded the threshold level. To date, this species has not yet developed resistance to insecticides.
When monitoring of leafhopper nymphs indicates that insecticide sprays are required, apply one of the materials listed in Pest Control Products Recommended for Use on Grapes in British Columbia.
It is often sufficient to spray small areas or treat only the perimeter of the vineyard. Spraying in this fashion is more economical and helps preserve beneficial insects. Although reduced rates (640 ml/ha) of carbaryl (Sevin XLR Plus™) suggested in earlier editions of this guide to help preserve beneficial insects are likely sufficient to control VCLH, full label rates will provide only moderate control of the more resistant WGLH. Malathion is currently registered for the control of leafhoppers on grapevines but it is unlikely to be effective against the WGLH. Assail™ (acetamiprid) has been shown to be repellent to adults and will cause them to move to unsprayed portions of the vineyard. Sprays should be targeted against small nymphs. Although Assail is less damaging to some beneficial insects compared with many broad-spectrum insecticides, it is toxic to predacious thrips and can cause spider mite numbers to increase. Safer’s Insecticidal Soap applied for the control of mites and grape mealybug will reduce leafhopper numbers somewhat. Apply soap in high volume sprays and ensure that the bottom leaf surfaces are covered thoroughly. Recent research at AAFC-PARC Summerland has shown that some newer fungicides and surfactants are repellent to adult leafhoppers and their use might eliminate the need for additional sprays. Increased movement of adult leafhoppers within and between vineyards requires greater vigilance, however.