5 Crop Protection 5.3 Insect & Mite Pests of Grape Revised February, 2015 D. Thomas Lowery, AAFC-PARC, Summerland Biological Control of Insects and (Graphics by Robyn DeYoung) Mites Insect and mite pests of grapes are attacked by Fewer insect and mite pests attack grapes grown many species of beneficial organisms, including in British Columbia compared with many other bacterial and viral diseases, spiders, insect major grape producing regions, which allows for predators, predacious mites, and vertebrates a ‘softer’ approach to pest management that such as toads and birds. Maintaining and preserves beneficial insects and predacious enhancing numbers of these natural ene- mites that help regulate secondary pests such as mies of grape pests forms the cornerstone of spider mites and grape mealybug. Adoption of a successful IPM program. Healthy popula- integrated pest management (IPM) practic- tions of predators and parasites prevent es that minimize the use of chemical sprays outbreaks of secondary pests and reduce the can also help reduce production costs, numbers of sprays required for the control of reduce human exposure to insecticides, and primary pests such as leafhoppers and climbing preserve the local environment. Insect and Mite cutworm. Pests of Grape in British Columbia (Lowery et al., 2014), a companion publication contains colour Beneficial organisms can be preserved or photographs of many of the pests outlined in enhanced in several ways. The negative impact this chapter of the production guide. In the of pesticides can be minimized by spraying only following descriptions of grapevine pests, when and where required. Monitoring of pest numbers and letters indicated in parentheses numbers will often indicate that only a small refer to the pages and plates of the correspond- portion of a vineyard requires chemical treat- ing photo guide. Additional sources for ment. Selecting the most appropriate spray information on insect and mite pests of grapes material will help reduce damage to non-target are listed at the end of this section. organisms. Compared with broad-spectrum insecticides that are often more toxic to benefi- Integrated Pest Management cial insects than the pests they are intended to control, insecticides that are less damaging to IPM utilizes a number of principles and practic- beneficial insects and predacious mites (e.g. es to manage pest populations, including AltacorTM) should be chosen whenever possible. biological, cultural, and physical control meth- Malathion is considered to be less damaging to ods. Insecticides remain an essential beneficial insects and mites than other insecti- component of an IPM program, but they are cides in the same class (organophosphates), and applied as a last resort only when monitor- carbaryl (Sevin XLRTM) can be used at a low ing has shown that pest numbers are likely rate when the target is the susceptible Virginia to exceed the economic threshold. When creeper leafhopper rather than the more re- insecticides are required, their selectivity, persis- sistant western grape leafhopper. Other tence, and effects on non-target organisms materials, such as the microbial insecticide Dipel should be considered. Some have minimal (B.t.), are highly selective and require that the effects on beneficial insects and predacious pest consumes the treated plant part, reducing mites, while others cause significant reductions toxicity to most non-target species. As listed in in natural enemy populations. A brief descrip- the BCMAL fact sheet ‘Pest Control Products tion and a few examples of the various Recommended for Use on Grapes in British Columbia’, components of a grape IPM program are (http://www.agf.gov.bc.ca/cropprot/grapeipm outlined below. For additional information, /grape_pesticides.pdf), all of the Class 4 (neon- refer to the Integrated Pest Management section icotinoid) insecticides (AssailTM, ClutchTM, (5.1) of this guide. CloserTM) combined should not be applied more than twice per season to avoid mite outbreaks. Best Practices Guide for Grapes for British Columbia Growers 5.3-1 5 Crop Protection These materials are listed as toxic to bees. The water and nutrients. Recent research in Califor- Class 3 pyrethroids (PounceTM, AmbushTM, nia has shown that deficit irrigation from berry RipcordTM) and natural pyrethrins (PyganicTM) set to veraison reduced leafhopper numbers by are toxic to most beneficial insects, but they more than 60%. The modest reduction in yield, persist in the environment for only a short time. around 15%, was more than offset by a signifi- cant improvement in wine quality. In addition, Thoughtful choice of management practices can berries were smaller and exposed to more light also help preserve beneficial insects. Mowing and air and pruning costs were slightly lower. less often and mowing only alternate rows at The presence of broadleaf weeds in and be- one time are simple and cost effective ways to tween vine rows is associated with lower levels increase populations of most natural enemies. of cutworm damage. In spring, when possible Adults of many beneficial species feed on nectar avoid controlling shepherd’s purse and other of flowering plants that also serve as hosts for weeds in the vine row until after buds have alternate prey species. As a general rule, in- broken, as removal of these alternate sources of creased plant diversity is associated with greater food forces cutworm larvae to feed more on the numbers of beneficial insects. A diversity of buds of grapes. plants can be provided in the vineyard in mixed ground covers, or in hedgerows and uncultivat- ed areas within or adjacent to the vineyard. Pruning Pruning can be altered to help reduce damage Cultural and Physical Controls from cutworm larvae. Slightly more buds can be Vine Vigour and Resistance left on vines to compensate for damage, but this will require the removal of more unwanted For most crops, varieties can be selected that shoots later in the season. Some growers delay are partially or wholly resistant to one or more suckering and shoot thinning to divert some pests and diseases. Except for rootstocks that leafhopper feeding and egg-laying to these are resistant to grape phylloxera or nematodes, unwanted plant parts. Thinning of the canopy this is generally not a viable option for wine by shoot removal, shoot positioning, and grapes. Most desirable wine grape varieties removal of basal leaves improves air flow and possess little resistance to foliar feeding pests. light penetration, which is important for the Vine vigour does, however, influence insect and management of diseases as well as insects. mite numbers. Leafhoppers and grape mealy- bug, for example, will reach significantly higher Leafhoppers and erineum or blister mite infest numbers on overly vigorous vines as they prefer the first leaves that emerge in spring, and these the darker, sheltered environment and elevated lower leaves can be removed in June to reduce humidity that excessive vine growth provides. numbers of these pests. A study conducted in Insects developing on these plants survive commercial British Columbia vineyards showed better and grow faster due to better nutrition, that removal of basal leaves in June rather than softer tissues, and changes in concentrations of August reduced numbers of leafhoppers and the secondary plant compounds. At the other incidence of bunch rot. Vine vigour and berry extreme, chlorotic vines with low vigour are less size were reduced only slightly and there was able to tolerate insect feeding damage and are little effect on ripening or quality of fruit. Early more susceptible to attack by hard scale insects season leaf removal might not be suitable for and wood boring beetles. Fortunately, the stressed vines or vines on sandy sites with optimum balance in vine growth that results intense heat and light where fruit can become in the highest quality wines is also best for sunburned. As for late season removal, partial minimizing the growth of pest populations. removal of leaves from only the shaded sides of the vines might be more suitable in these areas. Management of vine vigour is an important consideration in the establishment of a new Physical controls vineyard and is discussed elsewhere. After vines are established, growth is controlled by pruning, For some vineyards, the use of yellow sticky cropping, selection and management of appro- tape applied below the cordon in spring can be priate ground-cover plants, and the provision of an economical way to manage leafhoppers. 5.3-2 Best Practices Guide for Grapes for British Columbia Growers 5 Crop Protection Although costly, this physical control method that begin laying eggs at this time. Thrips preserves beneficial insects and reduces or damage table grapes from 75% bloom to fruit eliminates the need for additional insecticides set, and if scale or mealybug were noted earlier, later in the season. Use of yellow sticky tape is sprays can be timed based on the presence of most practical in vineyards where damaging crawlers. The need to spray for first generation numbers of leafhoppers occur in small, isolated leafhoppers should be based on monitoring for areas or on a few outer rows of the vineyard. small nymphs from mid June to mid July, while Other physical controls include pruning out of second generation nymphs will reach their peak canes infested with scale insects and application usually after the first week of August. In sum- of barriers to prevent climbing cutworm from mer, the presence of soft scale and mealybug is reaching developing buds. often betrayed by the presence of honeydew and attendant ants. Throughout summer, Monitoring and Chemical Controls monitor for thrips, spider mites and grape leaf Insecticides should only be applied when rust mite. For table grapes, watch for mealybug monitoring indicates that sprays are warranted. infesting clusters in mid-summer and for snail- The mere presence of a pest does not indi- case bagworm and earwigs closer to harvest.