5 Crop Protection 5.3 Insect & Mite Pests of Grape October 2020 Edition when monitoring has shown that pest D. Thomas Lowery, AAFC-SuRDC, Summerland numbers are likely to exceed the economic (Graphics by Robyn DeYoung) threshold; i.e. when the derived economic benefits exceed the costs of control. When Grapes grown in British Columbia are attacked insecticides are required, their selectivity, persis- by few insect and mite pests relative to those in tence, and effects on non-target organisms many other major production areas. Economic should be considered. Some have minimal losses from a small number of ‘key’ pests can be effects on beneficial insects and predacious considerable, however, requiring that producers mites, while others cause significant reductions implement timely and appropriate control in natural enemy populations. A brief descrip- measures. Although many growers in BC utilize tion and a few examples of the various conventional spray programs, the small number components of a grape IPM program are of economically important insect pests of grapes outlined below. For additional information, in this region more readily allows for adoption refer to the Integrated Pest Management section of sustainable and organic approaches to pest (5.1) of this guide. management that includes preservation of beneficial insects and predacious mites that help Biological Control of Insects and regulate secondary pests such as spider mites Mites and thrips. Adoption of sustainable* and Insect and mite pests of grapes are attacked by integrated pest management (IPM) practic- many species of beneficial organisms, including es that minimize the use of chemical sprays bacterial and viral diseases, spiders, insect reduces production costs and human expo- predators and parasitoids, predatory mites, and sure to insecticides and helps preserve the vertebrates such as toads and birds. Maintain- local environment. The companion to this guide, Insect and Mite Pests of Grape in British Columbia (Low- ing and enhancing numbers of these natural ery et al., 2014), contains colour photographs of enemies of grape pests forms the corner- many of the pests outlined in this chapter. In stone of a successful IPM program. Healthy the following descriptions of grapevine pests, populations of predators and parasitoids pre- numbers and letters indicated in parentheses vent outbreaks of secondary pests and also refer to the corresponding pages and plates of reduce the numbers of sprays required for the the pest photo guide. Beneficial Insects and Mites of control of primary pests such as leafhoppers. Grape in British Columbia, (Lowery et al. 2015) Beneficial organisms can be preserved or contains photos of natural enemies of grape enhanced in several ways. The negative impact pests. Additional sources for information on of pesticides can be minimized by spraying only insect and mite pests of grapes are listed at the when and where required. Monitoring of pest end of this chapter. numbers will often indicate that only a small portion of a vineyard requires treatment, and Integrated Pest Management selection of the most appropriate spray material will help reduce damage to non-target organ- IPM uses a number of principles and integrated isms. Broad-spectrum insecticides are often practices for the management of pests, including more toxic to beneficial insects than the pests biological, cultural, physical, and chemical they are intended to control. Insecticides that controls. Insecticides remain an essential are less damaging to beneficial insects and component applied as a last resort only predacious mites (e.g. AltacorTM) should be chosen whenever possible. Malathion is consid- *For details on the BCWGC Sustainable ered to be less damaging to beneficial insects Winegrowing British Columbia program, and mites than other insecticides in the same visit www.bcwgc.org/sustainable- class (organophosphates), and although it is an winegrowing-british-columbia. option for managing Virginia creeper leafhop- Best Practices Guide for Grapes for British Columbia Growers 5.3-1 5 Crop Protection per, Erythroneura ziczac, it will not control the better nutrition, softer tissues, and changes in western grape leafhopper, E. elegantula, that is concentrations of secondary plant compounds. resistant to this and other insecticides. Other At the other extreme, chlorotic vines with low materials, such as the microbial insecticide vigor are less able to tolerate insect feeding DipelTM (B.t.), are quite selective and require damage and are more susceptible to attack by that the pest consumes the treated plant part, wood boring beetles. Fortunately, the opti- reducing toxicity to most non-target species. As mum balance in vine growth that results in listed on the BC Ministry of Agriculture website the highest quality wines is also best for ‘Pest Control Products Recommended for Use on Grapes minimizing the growth of pest populations. in British Columbia’, all of the Class 4 neonico- Management of vine vigor is an important TM TM tinoid insecticides (Admire , Assail , consideration in the establishment of a new TM TM Clutch , Closer ) combined should not be vineyard and is discussed elsewhere in this applied more than twice per season to avoid guide. After vines are established, growth is mite outbreaks. These materials are listed as controlled by pruning, cropping, selection and toxic to bees. The Class 3 pyrethroids management of appropriate ground-cover TM TM TM (Pounce , Ambush , Ripcord ) and natural plants, and the provision of water and nutrients. TM pyrethrins (Pyganic ) are toxic to most benefi- Some of these practices can be manipulated to cial insects, but their activity persists for only 1- help manage grape pests. Recent research in 2 days to little more than a week. California, for example, has shown that moder- Thoughtful choice of management practices can ate deficit irrigation from berry-set to veraison also help preserve beneficial insects. Mowing reduced leafhopper numbers by more than less often and mowing only alternate rows at 60%. The modest reduction in yield, around one time are simple and cost-effective ways to 15%, was more than offset by a significant increase populations of most natural enemies. improvement in wine quality. In addition, Adults of many beneficial species feed on nectar berries were smaller and exposed to more light of flowering plants that also serve as hosts for and air and pruning costs were slightly lower. alternate prey species. As a general rule, in- The presence of broadleaf weeds in and be- creased plant diversity is associated with greater tween vine rows is associated with lower levels numbers of beneficial insects. A diversity of of cutworm damage. Having shepherd’s purse plants can be provided in the vineyard in mixed and other winter annual broadleaf weeds in the ground covers, or in hedgerows and uncultivat- vine row until after buds have broken can ed areas within or adjacent to the vineyard. provide effective control of cutworm. Removal of these alternate sources of food forces cut- Cultural and Physical Controls worm larvae to feed more on the buds of Vine Vigour and Resistance grapes. Perennial grasses in the vine rows should be managed over the summer, as they For most crops, varieties can be selected that compete with the vines and with these benefi- are partially or wholly resistant to one or more cial plants. pests and diseases. Except for rootstocks that are resistant to grape phylloxera or nematodes, Pruning this is generally not a viable option for wine grapes. Some hybrid grape varieties having Pruning can be altered to help reduce damage dense hairs on the leaf underside are less sus- from cutworm larvae. Slightly more buds can be ceptible to leafhoppers, but most desirable wine left on vines to compensate for damage, but this grape varieties possess little resistance to foliar will require the removal of more unwanted feeding pests. Vine vigor does, however, influ- shoots later in the season. Some growers delay ence insect and mite numbers. Leafhoppers and suckering and shoot thinning to divert some grape mealybug, for example, will reach signifi- leafhopper feeding and egg-laying to these cantly higher numbers on overly vigorous vines unwanted plant parts. Thinning of the canopy as they prefer the darker, sheltered environment by shoot removal, shoot positioning, and and elevated humidity that excessive vine removal of basal leaves improves air flow and growth provides. Insects developing on these light penetration, which is important for the plants survive better and grow faster due to management of diseases as well as insects. 5.3-2 Best Practices Guide for Grapes for British Columbia Growers 5 Crop Protection Leafhoppers and erineum or blister mite infest pest provides an economic return to the the first leaves that emerge in spring, and these grower. Sprays should be applied at the lower leaves can be removed in June to reduce appropriate time and life-stage of the pest. numbers of these pests. A study conducted in Monitoring of grape pests and determining commercial BC vineyards showed that removal thresholds is currently based mostly on visual of basal leaves in June rather than August inspections. Yellow sticky cards can be useful reduced numbers of leafhoppers and the inci- indicators of general population trends and pest dence of bunch rot. Vine growth and berry size developmental stages. Care should be taken to were reduced only slightly and there was little conduct a thorough inspection that takes into effect on ripening or quality of fruit. Early account the variable nature of the crop and the season leaf removal might not be suitable for uneven distribution of most grape pests. Partic- stressed vines or vines on sandy sites with ular attention should be given to field edges and intense heat and light where fruit can become to areas that have experienced damage previous- sunburned. As for late season removal, partial ly. The use of double sided clear tape applied removal of leaves from only the shaded sides of around shoots or the vine cordon can be used the vines might be more suitable in these areas.