Location: Horticultural Crops Research
2013 Annual Report
Ground covers and refugia confer a number of benefits on vineyards, including the attraction and retention of beneficial insects. A study demonstrated the value of some species of non-endemic annual flowering plants as ground covers to attract and retain various beneficial insects in south central Washington vineyards, with no adverse effects on vine growth. However, germination and survival of the cover crops was generally poor, due to the characteristically dry climate of south central Washington. A recent study in Michigan compared the attractiveness of selected perennial native plants and exotic annual plants to beneficial insects and found many native plants to be just as attractive, or more attractive than the exotics. The use of native perennial plants for ground covers and refugia has several benefits, including better adaptation to the local environment, aiding local biodiversity, and avoidance of annual establishment. In addition, native perennials may provide overwintering sites for beneficial arthropods. To restore native habitat refugia to Washington vineyards to enhance IPM and biological control, plant species with optimal attraction to predators and parasitoids of grape pests need to be selected.
No information is available on the attractiveness of native flowering perennial plants to beneficial insects in south central Washington.
One hundred and six species of flowering perennial plants were evaluated for beneficial insect attraction. The vast majority of these are native and all plants were growing wild in natural shrub-steppe landscapes in the Yakima Valley and nearby areas. Studies were primarily conducted at 5-6 sites near Yakima, Prosser and the Tri-Cities during April-November. The number and identity of beneficial insects attracted to different plant species was assessed using clear sticky traps (12 x 4 inches) placed either on the flowering plant or immediately adjacent to the plant. Control traps, placed on bare ground, rocks or dry non-flowering vegetation were also positioned near target plants. All groups play a role in regulating grapevine insect and mite pests in eastern Washington vineyards. For each assessment a single trap was used to assess attraction to each of three separated (at least 5 meters) individual plants. Traps were left in the field for 1-3 weeks, retrieved, taken to the laboratory, stored and examined later for beneficial insects under the microscope. Most plants were evaluated at multiple sites. Insects were identified to species or family, counted and recorded. All data were converted to means per trap per trapping period.
More than 1000 traps were deployed on 103 species of flowering perennial plants. Of these, 73 species were evaluated on at least 3 occasions. Sagebrush (Artemesia tridentata) somewhat surprisingly, was ranked the number 1 species but this was due to its attraction to large numbers of parasitic wasps which accounted for > 90% of the beneficial insects attracted. Similarly, the number 2 species, Gray Rabbitbrush (Ericameria nauseosus) was also strongly attractive to parasitic wasps (> 90% of attracted insects). The third species, Oregon sunshine (Eriophyllum lanatum) was also biased towards one group, but this time it was beneficial flies (> 80%). Slender Hawksbeard (Crepis atribarba) was also heavily biased towards flies (> 80%) but the remaining species in the top ten were more balanced in their attraction to a wider variety of beneficial insects. Western clematis (Clematis ligusticifolia), Northern buckwheat (Eriogonum compositum), Showy milkweed (Asclepias speciosa) and Snow buckwheat (Eriogonum niveum) attracted large numbers of beneficial insects from all groups. Parasitic wasps and beneficial flies still made up the majority of insects attracted to these four species, although Clematis attracted large numbers of predatory bugs and Northern buckwheat was the best plant for attracting ladybeetles. Milkweed was the best plant for attracting bees.
When all groups of beneficial insects are combined the mean number collected per trap in ranged from a low of 8 (Big-headed clover) to a high of 505 (Sagebrush) for the 73 plant species for which there are data for at least three trapping periods. The top ten species ranged from 150-505. The top 20 species had means > 75. About half of the 73 species trapped means of less than 50 beneficial insects. However, some of these may have value in attracting specific beneficial insects (e.g. Stinging nettle attractive to predatory bugs).
To date, results from 10 of the ~ 100 plant species evaluated have been analyzed. Snow buckwheat, Northern buckwheat, Gray Rabbitbrush, Milkweed, Western clematis, and Oregon Sunshine all produced results similar to those obtained earlier. Yarrow (Achillea millefolium) ranked # 9 in early collections (mean of 170 beneficial insects/trap) improved considerably in later collections with 432/trap (80% parasitic wasps). Completion of species attraction analysis is expected in late 2013.
Evaluation of the pest and beneficial insect fauna associated with habitat-enhanced (NHR) and habitat-reduced (control) vineyards.
Ten commercial vineyards are cooperators in this multi-season study. A pair of vineyards was identified and selected in each of the Columbia Gorge, Columbia Basin, Walla Walla and Quincy-Mattawa viticultural areas. In addition, NHR vineyard was monitored in the Columbia Basin and Walla Walla areas. Each area had one or two ‘native habitat-enhanced’ (VH) and a ‘native habitat-reduced’ (C) vineyard. Habitat-enhanced vineyards are situated close to natural areas with current management practices designed to maximize colonization of native plants in and/or around vineyards. Habitat-reduced vineyards are situated away from natural areas and colonization of native plants has not been encouraged and usually actively discouraged. Monitoring of pest and beneficial insect and mite populations commenced in all vineyards in May, continuing at two-weekly intervals until September. On each visit leaf samples were taken from grapevines and sticky yellow traps were placed in the vineyard. Leaves were examined in the laboratory for pests and beneficial insects and mites as were sticky traps. Additional sticky traps were placed in native habitats present adjacent to the habitat-enhanced vineyards.
Inventories of flowering plants and butterflies were obtained for each vineyard site during fortnightly visits. As expected, the habitat-enhanced vineyard sites had greater numbers of flowering plant species than habitat-reduced sites. Similarly, most habitat-enhanced vineyards appeared to support greater numbers of butterflies, both in abundance of individuals and species diversity.
Beneficial insect abundance as determined by sticky trapping was significantly greater at habitat-enhanced than habitat-reduced vineyard sites. This trend was evident in all major beneficial insect groups when examined separately including the important grape leafhopper parasitoids, Anagrus spp. Examination and analysis of beneficial insect abundance and diversity in habitat areas around the habitat-enhanced vineyards, indicated that some beneficial insect groups dispersed more effectively to the vineyard than others. For example, parasitic wasp abundance was substantially greater in surrounding habitat than in 2 ‘enhanced’ vineyards at Red Mountain. In contrast beneficial beetles and bugs in the Columbia gorge were more abundant in the habitat-enhanced vineyard than in surrounding habitat. Grape pest levels were generally low in all vineyards but there was a clear trend for greater incidence of mites, leafhoppers, mealybugs and scale insects in habitat-reduced vineyards compared to habitat-enhanced vineyards. The numbers of beneficial mites (predators of rust and spider mites) on leaves did not differ greatly between habitat-reduced and enhanced vineyards suggesting beneficial insects respond better to habitat improvement.
These data support the hypothesis that adjacent native habitats supporting a diverse community of native plants can be an important source of some groups of predators, parasitoids and pollinators, instrumental in providing effective and sustainable ecosystem services (e.g biological control of grape pests) in vineyards. In addition to providing direct and tangible benefits to viticulture, vineyard habitat restoration also has the potential to help conserve threatened flora and fauna including threatened native bees and butterflies. While butterflies were more abundant and diverse in habitat-enhanced vineyards, populations were generally small. Providing specific plants needed by specific butterfly species for development of immature stages has the potential to make vineyards suitable habitats for a number of eastern Washington butterflies.