Insects and Mites

Grapes grown in B.C. are attacked by few insect and mite pests relative to those in many other major production areas. Economic losses from a small number of key pests can be considerable, however, requiring that producers implement timely and appropriate control measures.

Although many growers in B.C. utilize conventional spray programs, the small number of economically important insect pests of grapes in this region more readily allows for adoption of sustainable and organic approaches to pest management that includes preservation of beneficial insects and predacious mites that help regulate secondary pests such as spider mites and thrips.

Adoption of sustainable and integrated pest management (IPM) practices that minimize the use of chemical sprays reduces production costs and human exposure to insecticides and helps preserve the local environment.

IPM uses a number of principles and integrated practices for the management of pests, including biological, cultural, physical and chemical controls.

Insecticides remain an essential component applied as a last resort only when monitoring has shown that pest numbers are likely to exceed the economic threshold, i.e. when the derived economic benefits exceed the costs of control. When insecticides are required, their selectivity, persistence and effects on non-target organisms should be considered. Some have minimal effects on beneficial insects and predacious mites while others cause significant reductions in natural enemy populations.

Biological Control

Insect and mite pests of grapes are attacked by many species of beneficial organisms, including bacterial and viral diseases, spiders, insect predators and parasitoids, predatory mites and vertebrates such as toads and birds.

Maintaining and enhancing numbers of these natural enemies of grape pests forms the cornerstone of a successful IPM program. Healthy populations of predators and parasitoids prevent outbreaks of secondary pests and also reduce the numbers of sprays required for the control of primary pests such as leafhoppers.

Beneficial organisms can be preserved or enhanced in several ways.

Be mindful of pesticides

The negative impact of pesticides can be minimized by spraying only when and where required. Monitoring of pest numbers will often indicate that only a small portion of a vineyard requires treatment, and selection of the most appropriate spray material will help reduce damage to non-target organisms. Broad-spectrum insecticides are often more toxic to beneficial insects than the pests they are intended to control. Insecticides that are less damaging to beneficial insects and predacious mites should be chosen whenever possible.

Malathion is considered to be less damaging to beneficial insects and mites than other insecticides in the same class (organophosphates), but although it is an option for managing Virginia creeper leafhopper (Erythroneura ziczac), it will not control the western grape leafhopper (E. elegantula) that is resistant to this and other insecticides. Other materials, such as the microbial insecticide DipelTM (B.t.), are quite selective and require that the pest consumes the treated plant part, reducing toxicity to most non-target species.

For more information about chemical control, see the Pesticides page.

Retain a diversity of plants

Thoughtful choice of management practices can also help preserve beneficial insects. Mowing less often and mowing only alternate rows at one time are simple and cost-effective ways to increase populations of most natural enemies. Adults of many beneficial species feed on nectar of flowering plants that also serve as hosts for alternate prey species.

As a general rule, increased plant diversity is associated with greater numbers of beneficial insects. A diversity of plants can be provided in the vineyard in mixed ground covers or in hedgerows and uncultivated areas within or adjacent to the vineyard.

Cultural and Physical Control

Vine vigour and resisitance

For most crops, varieties can be selected that are partially or wholly resistant to one or more pests and diseases. Except for rootstocks that are resistant to grape phylloxera or nematodes, this is generally not a viable option for wine grapes. Some hybrid grape varieties having dense hairs on the leaf underside are less sus-ceptible to leafhoppers, but most desirable wine grape varieties possess little resistance to foliar feeding pests.

Vine vigour does, however, influence insect and mite numbers.

Leafhoppers and grape mealybug, for example, will reach significantly higher numbers on overly vigorous vines as they prefer the darker, sheltered environment and elevated humidity that excessive vine growth provides. Insects developing on these plants survive better and grow faster due to better nutrition, softer tissues and changes in concentrations of secondary plant compounds.

At the other extreme, chlorotic vines with low vigour are less able to tolerate insect feeding damage and are more susceptible to attack by wood boring beetles.

Fortunately, the optimum balance in vine growth that results in the highest quality wines is also best for minimizing the growth of pest populations. Management of vine vigour is an important consideration in the establishment of a new vineyard.

After vines are established, growth is controlled by pruning, cropping, selecting and managing appropriate ground cover plants, and providing water and nutrients. Some of these practices can be manipulated to help manage grape pests.

Recent research in California, for example, has shown that moderate deficit irrigation from berry-set to veraison reduced leafhopper numbers by more than 60%. The modest reduction in yield, around 15%, was more than offset by a significant improvement in wine quality. In addition, berries were smaller and exposed to more light and air and pruning costs were slightly lower.

The presence of broadleaf weeds in and between vine rows is associated with lower levels of cutworm damage. Having shepherd’s purse and other winter annual broadleaf weeds in the vine row until after buds have broken can provide effective control of cutworm. Removal of these alternate sources of food forces cutworm larvae to feed more on the buds of grapes.

Perennial grasses in the vine rows should be managed over the summer as they compete with the vines and with these beneficial plants.

Pruning

Pruning can be altered to help reduce damage from cutworm larvae. Slightly more buds can be left on vines to compensate for damage, but this will require the removal of more unwanted shoots later in the season.

Some growers delay suckering and shoot thinning to divert some leafhopper feeding and egg-laying to these unwanted plant parts. Thinning of the canopy by shoot removal, shoot positioning and removal of basal leaves improves air flow and light penetration, which is important for the management of diseases as well as insects.

Leafhoppers and erineum or blister mite infest the first leaves that emerge in spring, and these lower leaves can be removed in June to reduce numbers of these pests.

A study conducted in commercial B.C. vineyards showed that removal of basal leaves in June rather than August reduced numbers of leafhoppers and the incidence of bunch rot. Vine growth and berry size were reduced only slightly and there was little effect on ripening or quality of fruit.

Early season leaf removal might not be suitable for stressed vines or vines on sandy sites with intense heat and light where fruit can become sunburned. As for late season removal, partial removal of leaves from only the shaded sides of the vines might be more suitable in these areas.

Physical controls

For some vineyards, the use of yellow sticky tape applied below the cordon in spring can be an effective way to manage leafhoppers. Although costly to implement and remove, this physical control method can often reduce or eliminate the need for additional insecticides later in the season. In comparison to sprays of broad-spectrum insecticides, this method helps preserve beneficial insects.

Use of yellow sticky tape is most practical in vineyards where damaging numbers of leafhoppers occur in small, isolated areas or on a few outer rows of the vineyard.

Some other physical controls include the use of barriers to prevent cutworm larvae from reaching the buds, collection of cutworm larvae from vines at night and removal of infested shoots or leaves.

Monitoring and Chemical Control

Insecticides should only be applied when monitoring indicates that sprays are warranted. The mere presence of a pest does not indicate that a spray is required.

Established grapevines can tolerate moderate amounts of leaf damage and small numbers of pests may have little or no effect on vine growth and yields. Even when pests have reached damaging levels, sprays should be withheld until the economic benefit of treating the crop exceeds the cost of controlling the pest, taking into account the possible disruption of beneficial insects.

In other words, sprays should only be applied when pest populations reach the economic injury level where control of the pest provides an economic return to the grower. Sprays should be applied at the appropriate time and life stage of the pest.

Monitoring of grape pests and determining thresholds is currently based mostly on visual inspections. Yellow sticky cards can be useful indicators of general population trends and pest developmental stages.

Care should be taken to conduct a thorough inspection that takes into account the variable nature of the crop and the uneven distribution of most grape pests. Particular attention should be given to field edges and to areas that have experienced damage previously.

The use of double sided clear tape applied around shoots or the vine cordon can be used to assist with timing of sprays for the control of the young motile stages of grape mealybug and soft scale insects. Maintaining yearly spray records and mapping of pest damage severity can be a useful tool.

Grapevines should be monitored for pests throughout the year:

• It is easier to spot scale infestations during pruning or early in spring before leaves are present. Grapes need to be visually inspected frequently in spring when unopened buds are susceptible to cutworm and rootworm damage.
• When the first leaves have fully expanded, watch for early infestations of erineum mite and note the presence of leafhopper adults that begin laying eggs at this time.
• Thrips damage table grapes from 75% bloom to fruit set, and if scale or mealybug were noted earlier, sprays can be timed based on the presence of crawlers.
• The need to spray for first generation leafhoppers should be based on monitoring for small nymphs from mid-June to mid-July, while second generation nymphs will reach their peak usually after the first week of August.
• In summer, the presence of soft scale and mealybug is often betrayed by the presence of honeydew and attendant ants.
• Throughout summer, monitor for thrips, spider mites and grape leaf rust mite.
• For table grapes, watch for mealybug infesting clusters in mid-summer and for snailcase bagworm and earwigs closer to harvest.

For more information about chemical control, see the Pesticides page.

Types of Insect and Mite Pests

Major

The major insect and mite pests of grapes in B.C. are cutworm larvae that attack buds in spring, leafhoppers that feed on leaves throughout the summer, wasps that eat ripe fruit and annoy or sting workers, and mealybug and soft scale that transmit grapevine viruses. Grape phylloxera is an important pest of grapes worldwide, but it occurs at damaging levels in only a few scattered locations in the southern interior of B.C. and was discovered more recently on Vancouver Island.

Other than wasps and phylloxera, these pests are largely absent from the Lower Mainland and Vancouver Island.

In addition to the major pests listed above, producers of table grapes need to worry about spotted wing drosophila, earwigs and scarring of fruit by thrips. Earwigs do not cause direct damage to grapes but are considered a contaminant by many vendors of table grapes.

Proper management of these primary pests is the most important consideration in an IPM program.

Grape pests and the damage they cause needs to be recognized so that populations can be monitored at the appropriate time of the season to determine if insecticide applications are warranted. Avoiding unnecessary sprays will help prevent outbreaks of secondary pests that are normally regulated by an assortment of predators and parasitoids.

Secondary and minor

Several insect and mite pests of grapes occur infrequently or only cause significant amounts of damage after chemical sprays have reduced predator and parasitoid populations that normally regulate their numbers.

The best way to manage these pests, then, is to properly manage populations of primary pests in order to preserve and enhance numbers of beneficial insects and predacious mites.

Miscellaneous

In addition to the major and secondary grape pests described above, a number of insects attack grapes in B.C. only very rarely and are generally not of economic importance.

Prevention of New Grape Pests

Provincial entomologists, Agriculture and Agri-Food Canada researchers and Canadian Food Inspection Agency regulators and inspectors contribute to the prevention of the arrival of new invasive pests of grapevines into B.C.

Importation of host plant material from areas known to harbour these pests is regulated, and plants are inspected upon arrival or at the source nursery. Information is provided to industry members and the general public through talks, identification fact sheets and brochures.

It is inevitable that new, economically important pests of grapevines will arrive in our region from elsewhere. Growers can help prevent the establishment of new alien pests by knowing the species currently found in B.C. and reporting new pests and unfamiliar damage to grapevines.

The list of potential grape pests that might arrive in B.C. from elsewhere is very long. This best practices guide includes a few economically important ones and sources for additional information.

Other Resources

Environmental conditions, the grape pest complex and registered pesticides differ for B.C. as compared to other grape-producing regions.

• Agriculture: Pest Management Guidelines, Grape on the University of California Statewide Integrated Pest Management Program website
• 2019 pest management guide for wine grapes in Oregon on the Oregon State University's Scholars Archive website

Explore All Insects and Mites