Winter, 1990 (v2n2)
	500 Attend Low-Input Grape Meetings The success of a December 1988 reduced input grape meeting in Visalia prompted the presentation of three similar meetings in the fall of 1989. Each program was sponsored in part by UC Cooperative Extension and the UC SAREP. The October 24 meeting at Kearney Agricultural Center in Parlier, moderated by Bob Sheesley, Fresno County Cooperative Extension director, was attended by approximately 250 people. The meeting in Stockton on November 7, co-sponsored by the UC Statewide IPM Project and the Lodi District Grape Growers, was led by Stanislaus County Farm Advisor Kathy Kelley and drew about 90 people. The November 14 Santa Rosa meeting was co-sponsored by University Extension and moderated by Jim Wolpert, viticulture extension specialist at UC Davis and was attended by 190 people. New Vineyard Considerations Most of the presentations addressed practices which can reduce chemical inputs in existing vineyards. Paul Verdegaal, San Joaquin County viticulture advisor, and Jim Wolpert, however, discussed the importance of site and variety considerations in the initial establishment of a vineyard, and how their careful consideration can lead to reduced inputs later. Verdegaal spoke at the Stockton meeting, while Wolpert spoke at the Santa Rosa meeting. They identified three site characteristics which influence pest management strategies: soil type and depth, previous crop history, and location. Grape variety choices will in most cases be determined by overall market demand and/or buyer needs. When a choice exists, however, the use of certain varieties can mitigate potential insect, disease and nutritional problems, they said. Nutrition, Vine Management "The key to vine management is to adequately fill the trellis system without creating excessive vigor," said Pete Christensen, extension viticulture specialist, at the Kearney and Stockton meetings. Christensen said the rate of nitrogen (N) applied should be adjusted to account for potential vigor. He noted that recent research has shown maximum N uptake is during late spring or summer, rather than in winter or early spring. Postharvest applications have been shown to provide high levels of stored N at dormancy, supplying the N needs of early spring growth. Split fertilizations at these times have resulted in nearly a 50% decrease in N applied per acre in the southern San Joaquin Valley due to the increased efficiency of uptake, he said. Cover crops can be used either to add N (legumes) when deficient, or to compete with vines during the summer to control excessive vine vigor, according to Christensen. For maximum N availability, the legume should be incorporated in the spring just before it blooms, he said. Excessive vigor can be controlled by allowing a cover of Blando brome grass to mature (mowing before the frost period) and reseed. This practice will tie up N, delaying and extending its availability, he said. The use of a summer grass cover will also help control vigor due to increased competition for water and nutrients, and the cover will also reduce dust problems, Christensen said. Soil, Water Management Bill Liebhardt, SAREP director, reviewed the pros and cons of manures and composts at the Santa Rosa meeting. He discussed the process of organic matter decomposition. While both manures and composts improve soil tilth and add essential nutrients, nutrients in compost are more concentrated and are biologically more stable, he said. Terry Prichard, water management extension specialist at UC Davis, discussed his research at the Santa Rosa meeting. His work in almonds showed that when a cover crop of Blando brome grass is mowed in the spring, the clippings protect the soil surface, impede moisture loss, and act as a mulch to prevent weed seed germination. A residual herbicide treatment also resulted in low water use, but increased soil compaction, he said. Non-chemical weed control was UC Davis Extension Weed Specialist Clyde Elmore's topic at the Santa Rosa meeting. He said growers face two major weed management issues: any weeds in the vine rows of young vineyards, and perennial weeds in established vineyards. Elmore said various kinds of natural and synthetic mulches look promising, although some are very expensive. He said cover crops may out compete problem weeds with proper management, noting that Elka ryegrass has been shown to suppress 96% of other weeds. Grape IPM Bill Barnett, area Integrated Pest Management (IPM) advisor at Kearney, presented an overview of IPM principles in grape production at the Kearney meeting. He stressed the importance of cultural and biological control methods, but he said that chemical pesticides, with all their drawbacks, will continue to be a tool in pest management. He talked about the need to get off the "pesticide treadmill" by timing their applications to minimize the effect on non-target organisms, and by spot-treating problem areas which have been identified through extensive monitoring. Leaf Removal At the Kearney and Stockton meetings, Jim Stapleton, area IPM advisor in Stanislaus County, presented results from studies on wine grapes which indicated that selective leaf removal vastly reduces bunch rots, especially Botrytis. Stapleton recommended evaluating the effects of leaf removal on a small portion of acreage before using this technique on an entire vineyard. Mechanical leaf removal on wine grapes may become more cost effective and replace removal by hand, he said. Jim Marois, a plant pathology associate professor at UC Davis, continued the discussion of leaf removal at the Santa Rosa meeting. Botrytis stops growing beyond a certain "evaporation potential," and wind speed is the factor which most affects evaporation of moisture off grapes. The major effect of leaf removal is to keep grape clusters and the air surrounding them drier, which stops the spread of Botrytis, Marois noted. Cluster tightness is a more important factor in disease incidence than is individual berry susceptibility, he said. Further research may show that cluster manipulation may help prevent bunch rots, he said. Kenneth Hagen, a UC Berkeley entomology professor, spoke about insect predators and explained how leaf removal for control of bunch rots reduces the number of leaves which predators and parasites have to cover in search of prey, increasing their effectiveness. He said predators may play a strong role in vineyards, and should be encouraged by pollen, nectar and habitats provided by cover crops. Leafhoppers Leafhopper management was discussed at all three meetings. "The grape and variegated leafhoppers are the most important pests of grapevines in the San Joaquin Valley," according to Tulare County Farm Advisor Bill Peacock, who spoke at the Kearney meeting. He said that vine vigor is essential to reduce leafhopper populations. The parasitic wasp, Anagrus epos, is an effective natural enemy of the grape leafhopper, but only about 30% control of variegated leafhoppers can be expected, he said. Peacock emphasized that it is important to avoid using chemical insecticides unless absolutely necessary, due to mites' increased resistance to them, and to the disruptive effect insecticides have on mite predators. This requires knowing both the economic level of leafhopper populations and the amount of egg parasitism, especially during the first brood, he said. Control of these first brood nymphs is important and can be done using soaps or summer oils; leaf removal has also been shown to be effective. Bill Barnett discussed leafhopper management at the Stockton and Santa Rosa meetings. He said vineyards in the Stockton/Lodi area nearly always have Anagrus parasites due to the large number of riparian areas containing blackberry vines. Blackberries, as well as prunes and possibly almonds act as alternate hosts of the parasite during the winter. The variegated leafhopper, however, has recently moved into the northern San Joaquin Valley and is moving toward northern coastal areas. New Anagrus parasites from Mexico, Arizona and Colorado have been introduced into California in an attempt to provide increased biological control. Barnett also stressed that general predators, especially spiders, can be important in leafhopper control, and that cover crops will greatly increase the population of such predators. Mites, Mealybugs The management of mites, a pest which often flares up after insecticidal applications for leafhoppers, was addressed at the Kearney meeting by Harry Andris, Fresno County farm advisor. He said cultural considerations that help reduce mite damage include avoiding water stress to the vines, reducing dusty conditions, and providing a habitat for mite predators. Summer cover crops or a native weed cover provide such an habitat and are gaining in popularity. Don Flaherty, entomology farm advisor in Tulare County, discussed mealybug management at the Kearney meeting. Mealybugs overwinter on old wood under loose bark and readily infest bunches which later touch the cordons (woody part of grape plant). Some growers are using arbors, allowing the clusters to hang free from old wood. If spraying must be done, spot-spraying can minimize damage to parasites, he noted. Spray Oils New approaches to pest control were addressed at the Kearney meeting by Jack Dibble, entomology specialist at Kearney. He said that narrow range spray oils that are effective against certain insect and mite pests of tree and vine crops, are inexpensive and very safe. Because the mode of action is through suffocation, thorough spray coverage is important, he said. Soaps are also quite safe and show effectiveness on mites and both species of leafhoppers, Dibble said. Vacuum machines have recently received attention and some growers have reported 40-50% control of leafhoppers, he added. Nematodes Mike McKenry, extension nematologist at Kearney Agricultural Center, talked about nematode management at the Stockton and Santa Rosa meetings. He noted that many commercial nematicides may soon become unavailable, and discussed alternatives including resistant rootstocks, more frequent irrigation, manuring, cover crops, and soil amendments. Each of these may have drawbacks and some are expensive, he said. Many plant extracts are toxic to nematodes, but have also been found to be toxic to plant roots, he said. Finally, while some cover crops have been found to restrict vine growth, McKenry said the following three winter covers seem to be compatible with grapevines and do not harbor nematodes: Cahaba white vetch, barley, and Blando brome grass. The Stockton meeting also included a panel discussion with two local growers. John Tecklenburg, from Lodi, became frustrated with the excessive use of Furadan and the buildup of root knot nematodes in his farming operation. He explained how implementing IPM techniques helped him reduce mite buildup while improving his general farm management practices. Joe Cotta, whose family has been farming since 1966, noted that their operation started without a spray rig. He said they eventually joined most growers on the "pesticide treadmill." When problems arose with the use of the pesticide Metasystox-R (MSR) on grapes, they began to examine their farming techniques. They now successfully farm a portion of their vineyard with no chemical sprays. Index for Sustainable Agriculture Winter, 1990