In addition to the widespread Virginia creeper leafhopper (VCLH) (Erythroneura ziczac), the western grape leafhopper (WGLH) (E. elegantula) — which was first found in B.C. in 2007 infesting grapes on the east side of the Okanagan Valley from the north end of Penticton south to the U.S. border — has now spread throughout much of the Okanagan Valley and into parts of the Similkameen Valley.
Sharpshooters — including the poplar sharpshooter (Neokolla heiroglyphica) and the willow (purple) sharpshooter (N. confluens) — occasionally infest the shoots of grapevines in sufficient numbers to warrant control.
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.
Adults of both species are similar in appearance, nearly 0.5 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.
Nymphs of both species can be identified feeding on the undersides of fully expanded leaves that show signs of feeding damage (stippling).
Immature WGLH (nymphs) are distinguished by their pale white colour, eyes appearing red due to lack of pigmentation and the presence of 1-3 pairs of pale indistinct yellow spots on the thoracic segments of larger nymphs. Under magnification, a double row of longer spine-like hairs are visible on the upper side of the abdomen.
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.
The dark coloured adults appear oversized in relation to the other leafhoppers found on grapes in B.C., and they have more pronounced triangular shaped heads. The large nymphs appear a uniform brown colour.
The biology and life cycles of the two species are similar: there are two generations each year, with occasionally a partial third.
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 2-6 for VCLH and singly for WGLH. Nymphs of this first generation emerge from mid-June to the end of July. There are five nymphal stages.
Winged adults that appear in July and August lay eggs that produce the second generation nymphs 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 fruit 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.
Leafhoppers are often distributed unevenly in vineyards, and monitoring will help determine which areas require treatment.
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 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 are repelled by some materials. Therefore, sprays should be targeted against the wingless immature stages.
Infestations of sharpshooters are generally restricted to vines growing in close proximity to the preferred host plants after which these species are named. There are no chemicals registered for the control of sharpshooters in B.C., but sprays applied for the control of leafhoppers should also help control these species.
Experience has shown that WGLH numbers are generally lower in organic vineyards.
Special considerations are required when managing leafhoppers in organic vineyards. Soaps and oils are not as effective as conventional insecticides, and because B.C. currently lacks certain effective organic spray materials widely used elsewhere, control of leafhoppers in organic vineyards here is currently very difficult, requiring usually several complimentary practices. As such, it is best to take preventative actions and to consider the action threshold to be extremely low.
Depending on the location of the vineyard, monitoring of first generation nymphs should begin in early to mid-June. Monitor populations by counting the numbers of nymphs on the lower surfaces of 5-10 leaves in at least five 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 first generation nymphs.
The threshold of approximately 20-25 nymphs per leaf established for the second generation in late summer can also be used as an approximate threshold for early summer sprays. A higher threshold can be used for first generation nymphs if healthy populations of predators are present and a high rate of parasitism is likely.
Control of first 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 and oil sprays are much more effective when targeted against first generation nymphs when most 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.
Second generation nymphs should be monitored beginning in late July or early August in a manner similar to that outlined above. Greater attention should be paid to vines in the centre of the field as infestations will have spread from field edges and hot spots to a larger area of the vineyard.
Nymph counts should be collected at least weekly as the time for spraying approaches. For wine grapes, an approximate threshold of 20-25 nymphs per 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 5-10 leaves from at least five areas and calculate the average number of nymphs per leaf. For second 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 adequately 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 vigor and numbers of beneficial insects.
Unnecessary sprays reduce numbers of beneficial insects and spiders and can result in a rapid resurgence in pest numbers and outbreaks of thrips, mites, mealybugs and soft scale.
Damaging populations in conventional vineyards generally result from repeated sprays of insecticides that do not control this species but damage numbers of its most important natural enemy: the egg parasitoid Anagrus erythroneurae. (See the biological control section below for more details.)
Natural enemies should be preserved by applying the lowest effective rate only to areas where the pest has exceeded the threshold level. 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.
Neonicotinoids and other broad-spectrum insecticides are toxic to predacious thrips and beneficial insects and have been shown to cause increases in spider mites and other secondary pests. AssailTM is also repellent to adult leafhoppers and will cause them to move to unsprayed portions of the vineyard. Sprays should, therefore, be targeted against small nymphs.
Research at the Summerland Research and Development Centre has shown that certain strobilurin fungicides and some organosilicone surfactants are also repellent to adult and immature leafhoppers. Their use might eliminate the need for an insecticide spray, but this increased movement of adult leafhoppers within and between vineyards requires greater vigilance.
The WGLH is more tolerant of insecticides, and it is important to determine relative numbers of the two species in your vineyard. Malathion, for example, is an option when the leafhopper population is almost entirely VCLH, but its use can result in increased numbers of the resistant WGLH.
Some insecticides registered for leafhopper control are ineffective against WGLH, and it is important to determine if this species is present in your vineyard. Malathion is ineffective against the WGLH that is resistant to this and other insecticides. The VCLH has not developed resistance to insecticides.
For more information about chemical control, see the Pesticides page.
Predators — such as birds, spiders and several species of hemipteran bugs — and parasitic wasps attack leafhopper eggs, nymphs or adults.
Although occasionally contaminating table grapes, earwigs consume large numbers of leafhopper eggs, leaving behind small, shallow scraped areas on the undersides of leaves.
A small egg parasitoid, Anagrus daanei, helps control VCLH in some vineyards where parasitism rates can approach nearly 100% late in the season.
A different parasitoid, A. erythroneurae, parasitizes eggs of the WGLH and is largely responsible for the biological 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 parasitoid utilizes eggs of a leafhopper on a wide range of mints, including catnip and catmint.
Most vineyards have good numbers of A. erythroneurae, and outbreaks of WGLH are largely associated with sprays of insecticides that do not control this leafhopper but are toxic to the parasitoid. Excessive rates or unnecessary insecticide sprays 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 superior quality wine grapes.
The use of yellow sticky tape applied below the cordon in spring, just before bud break, can be an economical way to manage leafhoppers in some vineyards. Although costly, this method helps preserve beneficial insects relative to insecticide sprays. 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 study conducted by researchers at the Summerland Research and Development Centre, beginning in 2001, demonstrated that the removal of basal leaves during the second and third weeks of June, when most eggs of the first generation had been laid, effectively reduced numbers of leafhoppers by about 70%. As an added benefit, early season removal of leaves from the fruiting zone also reduces the amount of bunch rot. No significant differences were noted in fruit quality other than a slight reduction in yield and berry size.
This practice might not be suitable for stressed vines or on sites with intense heat and light that might lead to sunburn. However, sunburn is less likely to occur following early removal of leaves (June) as compared to late removal (August).
Exposure to light and air causes developing berries to produce thicker skins and more wax, and the subsequent growth of lateral shoots will provide some shading. This practice is labour intensive, but many growers routinely remove leaves from the fruiting zone later in the season in order to improve fruit quality. Mechanized removal of leaves offers an approach, perhaps a little less effective, that might be more cost effective over time.
