Final Report for LNE90-020
This study evaluates methods to convert commercial vineyards of juice and wine grapes to organic culture, develops new, non-pesticidal methods to control vineyard weeds, pest and diseases and documents the economic impact of altered production practices. Following the three year conversion interval required for certification, certifiable organic grapes were produced successfully in 1993 and 1994. The study has demonstrated that insects and disease were adequately controlled in vineyards of American and disease resistant French-American varieties in the humid climate of the east. It has been further shown that replacing synthetic fertilizers with a combination of natural manures and legume cover crops can satisfy the nutritional requirements of the grapevine. However in dry years, yields of organically managed vines have been lower than yields of conventionally managed vines. For Concord and Seyval, mean 5 year yield was reduced for organically managed vines. There was no yield difference for the third variety, Elvira. Indications are that the primary limitation in the organic vineyards has been water availability. A combination of improved floor management technology and irrigation offers the hope to moderate these limitations. Related research promises to further reduce the dependence on pesticides by identifying and utilizing biological control agents to suppress weed growth, fungal disease and insect populations.
The project site is at Taylor Wines in Dresden, New York approximately fifty miles south of Lake Ontario in Central New York's Finger Lake Region. The vineyards are about two miles from the western shore of Seneca Lake at an elevation of approximately 250 feet. Soils at the site are classified as Lima Silt Loam which are moderately drained, medium texture high lime soils approximately 12-20 inches deep. The average growing season of the area is 200 days. Average yearly rainfall is 32 inches with an average 20.3 inches during the growing season. The study areas are divided into three 10-acre blocks (one for each cultivar - Concord, Seyval, Elvira). One half of each block is conventionally managed and the other half is managed organically.
1. Determine the impact of vineyard conversion on vine nutrition, soil fertility and moisture, vine vigor, capacity and yield.
2. Determine the impact of vineyard conversion on disease incidence and severity.
3. Compare the efficacy of survival of beneficial biological control fungi under conventional and organic management programs.
4. Determine the contribution of dormant eradicant treatments to seasonal disease control under conventional and organic management programs.
5. Demonstrate the efficacy of a non-pesticidal insect pheromone for control of grape berry moth; determine the long-term effects of eliminating conventional insecticides from vineyards; and develop risk assessment methods for management of grape leafhopper.
6. Determine the impact of vineyard conversion on fruit and wine quality.
7. Determine the impact of vineyard conversion on production costs and profitability.
8. Relay results of the study to growers using current Cooperative Extension methods.
A. Findings and Accomplishments: (By Objective)
Soil and Nutrients
After some initial nitrogen deficiency problems in the organic blocks in the first year, conventionally and organically managed vines were similar nutritionally. The chicken manure pellet fertilizer source provided a controllable and reasonably easy to handle source of nitrogen fertilizer. White clover as a row middle cover crop enhanced nitrogen uptake where established in the organic blocks. The chicken manure pellets also contained magnesium and calcium, which was advantageous in some blocks and problematic in others. Organically managed blocks were typically higher in soil phosphorus, magnesium, calcium and pH than conventionally managed blocks. Copper fungicides resulted in residues on soil petioles, but no meaningful buildup occurred in the soil.
Present floor management options open to organic grape growers are cultivation or a continuous cover. Our experience showed that, in dry years, organically managed vines suffer increased drought stress when the "natural" cover (mixed orchard grass and broad leaf weeds) which develops when Finger Lakes row middles are only mown, are used instead of the conventional glyphosate no-till approach. Legume covers appear to be at least as competitive as the natural covers. Tests with alternate cover crops have generally not verified reported benefits from reportedly low competition covers such as bluegrass, but inclusion of rye grass appears to offer real benefit. Decaying rye grass debris inhibits weed seed germination and reduces vine competition during critical periods. The result has been enhanced vine growth, yield and quality. These approaches need to be more broadly applied; the potential for allelotrophic suppression of in-the-row weeds should be evaluated.
Yield and Quality
Because row by row yield records had been recorded in 1989, we were able to show that there had been no significant yield differences between the experimental areas in the year previous to the initiation of the project for any of the three cultivars. Yields were not always affected by culture method during each year, but in general, yields of organic grapes were lower than yields of conventional grapes in years following a period of drought stress. An exception was Elvira. For Elvira overall yield did not differ significantly between the two systems, and in the two years when yield did differ, organic vine yield was higher than conventional yield in one year and lower in the other. Overall yields of organically grown Concords was about 20% lower than conventionally grown Concord and organic Seyval yield was reduced by about 30%.
There are two primary reasons for the difference. Even though we attempted to match blocks, it was apparent that the soil of the organically grown Seyval was inferior to the conventional soil. The primary difference was the extent of erosion in the organic section which meant that some areas had shallow soils with less water holding capacity and a greater requirement for potassium addition. We saw no similar difference in the Concord soils, but in general, the soil in the Concord blocks had higher pH. Because nutritional management is more complicated for Concord grapevines growing in a higher soil pH, and because organic management tended to increase soil pH and Magnesium content, the organic vines may have suffered in the short range. It would be very interesting to observe these vineyards during the next five year period when the benefits of five years of soil building by the organic management would be expected to increase the yield. A similar pattern of five years inferior yield followed by 5 to 10 years of equal or better yield of organically managed soils has been observed with annual crops.
The primary reason for the reduced yield of organic grapes was increased competition from weeds and cover crops. Until less competitive organically acceptable weed control measures are identified, growers must expect lower yield potential from organically managed vineyards.
Yields of organically grown grapes were lower than for conventional grape production. However, the reduced yields appeared to be primarily due to less efficient vineyard floor management options. These were more competitive with the grapevine, more expensive and, in many cases, less sustainable than best current grower practice. Research with cover crops and with new weed management is identifying new techniques which promise to reduce the level of vine competition without the need to resort to chemical solutions of weed control. It is possible that irrigation might be a substitute for more precise weed management. Quality did not appear to be directly related to method of cultivation, but when yield potential was affected, indirect crop load mechanisms, did affect grape and product quality.
Disease incidence and severity
Organic management practices appear to provide effective control of powdery mildew on foliage and fruit of Seyval. These practices consist of routine and frequent applications of sulfur (i.e., at 10 day intervals from early shoot growth to veraison). Copper fungicides used in the organic management treatments have provided acceptable control of powdery mildew on the moderately resistant cultivars Concord and Elvira. Organic management practices (use of copper and sulfur fungicides) may therefore provide acceptable control of powdery mildew on the above cultivars. However, copper fungicides will not provide reliable control of powdery mildew on mildew-susceptible cultivars, nor can the more effective mildewcide (sulfur) be used on sulfur-sensitive cultivars such as Concord. Organic management of powdery mildew depends upon the proper selection of cultivars with respect to available fungicides and varietal sensitivity to powdery mildew and these fungicides.
The absence of black rot in repeated disease assessments throughout the course of the study, and the absence of untreated controls as a component of the study confounds the interpretation of the results. Intensive control of black rot in the years preceding the study may have reduced initial inoculum to trace levels, allowing the fungicides used under the organic management practices, which have little efficacy against black rot, to contain the disease. The failure of black rot to develop in unsprayed Concord vineyards after years of intensive control is a well documented phenomenon. After 5 years of organic management, it is encouraging that black rot has not increased to damaging levels. However, we can not predict if the results obtained at our research sites can be extended to other vineyards that may have higher background levels of the pathogen. Alternate-year disease control, an idea suggested by our results in this project, is the subject of continued research.
Copper fungicides are the only option available under organic management practices for control of downy mildew, thus effective control of downy mildew is limited to copper-tolerant or disease resistant cultivars. Copper fungicides are highly effective, however, and the prospects for control of downy mildew with these materials are quite good. Our results over the five years of this study indicate that downy mildew can be controlled adequately under current organic management practices.
Phomopsis cane and leaf spot and fruit rot
The fruit rot phase of this disease was significant only during the final year of the study. However, based upon the known lack of efficacy of sulfur and copper compounds against this disease, it is unlikely to be adequately controlled in severe years. The development of severe disease in Seyval in 1994, a cultivar not known for its susceptibility to fruit rot, illustrates the importance of cultural practices to control this disease under organic management. Hand pruning and Umbrella-Kniffen training is known to provide a significant reduction of Phomopsis fruit rot, and should be used for reliable control under organic management.
Biological control of fungal disease
No new work was done with spores of the fungus, Ampelomyces quisqualis, which parasitize PM fungi in 1994. Previous work showed that spores dispersed by rain from cottons strings which had been soaked in spore suspension and hung over leaf canopies reduced disease in the wet year 1992, but failed to do so in the dry year, 1993, when PM incidence was low. A problem is that A. quisqualis is sensitive to the most effective PM control agents available to organic grape growers, sulfur. Impact of the fungal isolate, G6 on downy mildew (DM) caused by Pernospora viticola was tested at Geneva using more DM sensitive varieties. G6 reduced DM incidence and severity of both leaves and fruit.
Dormant season eradication of over wintering disease inocula
Despite the demonstrated success of dormant season applications of lime sulfur to eradicate over wintering PM, it appears that cost and other considerations will prevent industry adoption of the technique. As a result alternative methods to eliminate PM are being investigated. Lab studies showed a 1 min. exposure to 90°C produced 100% mortality of PM cleistothecia. Units to apply 90° water in the field were tested and failed to transmit sufficient heat energy. A prototype utilizing live steam or hot air was built. Best results were with hot air, but indicated further development of equipment will be required.
Non-pesticidal insect control
Grape Berry Moth
Over the five years of the study (Figure 5.2), percentage of infested berries at harvest was consistently below 2 % at the edge of the conventional blocks. In the organic blocks, edge injury exceeded 2% at harvest in 1992 (Concord) and in 1990, 1991, and 1992 (Elvira). In vineyard interiors, the highest amount of injury was observed in the conventional Elvira and Seyval blocks in 1993. However the injury observed was consistently under the industry standard of 2% damaged berries. Higher injury at the edges of the organic Concord and Elvira blocks reflects, in part, the physical layout of the blocks and their proximity to wooded areas that serve as sources of infestation. Damage levels were somewhat lower in the interiors of the Elvira and Seyval blocks, which may reflect suppression of berry moth by pheromone tie application. In the interiors of the pheromone-treated blocks, damage was comparable or lower than that observed in the conventional Elvira and Seyval blocks. One to two insecticide applications were made in 3 of the 5 years (Elvira) and 2 of the 5 years (Seyval) of the project. Observed injury levels at harvest were similar, and low in both pheromone-treated and insecticide-treated areas in all five years of the project.
Grape Leafhopper -- Five Year Summary of Nymphal Densities
Seasonal maximum leafhopper densities over the life of the project are shown in Figure 5.4. Leafhopper densities in all years of the project and all blocks were always well below the intervention threshold of 5 leafhopper nymphs per leaf. Highest densities attained over five years were 2, 2.5, and 1 nymphs per leaf in Concord, Elvira, and Seyval blocks, respectively. One to two insecticide applications (Sevin 80S, 2.5 lb/acre) were made to conventional blocks in 2 (Seyval) or 3 (Elvira, Concord) of the 5 years of the project No insecticides that controlled leafhoppers were applied to any of the organic blocks in any year. Maximum leafhopper densities were roughly equivalent in conventional and organic blocks over the life of the project.
This study has shown that the two major grape pests, grape berry moth and Erythroneura leafhoppers, did not cause economically-significant injury under either conventional or organic management practices over a period of five growing seasons. No major differences in infestation levels of these two pests were seen, despite significant differences in management practices.
In the conventional blocks, insecticide treatments that suppress both grape berry moth and leafhoppers were applied in two to three of the five growing seasons. In the organic blocks, materials applied for insect management (pheromone ties or Bacillus thurengiensis), are active only against grape berry moth, and have no effect on leafhoppers. ISOMATE-GBM specifically targets only grape berry moth; Bacillus thurengiensis (Dipel) is a selective material that controls only lepidoptera. In contrast, carbaryl is a broad-spectrum material that surppresses grape berry moth, leafhoppers, grape rootworm adults, and a wide variety of other beneficial arthropods present in vineyards.
Use of these more selective materials did not result in economic infestations of leafhopper in the organic blocks. Although leafhoppers were present in all blocks, they did not reach economically-significant population densities, despite the lack of treatments applied to organic blocks and the conventional blocks (in 2 of the five years, no insecticides were applied to conventional blocks). Several factors may have contributed to the low observed densities of leafhoppers in these blocks. First, the 15 acres managed 'organically' were a small proportion of the acreage of grapes present at the farm. Insecticide sprays on a majority of the blocks including, adjacent blocks may have contributed to low infestation levels on the entire farm. A second factor is varietal differences in susceptibility to leafhopper oviposition. (Martinson & Dennehy, in review). A complex of four different Erythroneura species are present in NY vineyards, and each species prefers for oviposition a different spectrum of grape varieties. Our observations in these and other blocks have suggested that some varieties, such as 'Seyval' and possibly 'Elvira', are not subject to heavy oviposition by leafhoppers, for unknown reasons. Concord grapes, are preferred for oviposition by E. comes; however the dominant leafhopper species present at Dresden, E. bistrata , does not oviposit heavily in 'Concord'.
Finally, a major factor that tends to limit leafhopper population growth is a minute endemic wasp , Anagrus epos, that parasitizes leafhopper eggs. The impact of this parasitoid is well documented in California, but had not been characterized previously in Eastern vineyards and with native American or hybrid grape varieties. Through this project, we were able to characterize the basic biology of A. epos under climatic and viticultural conditions present in the northeast. We found that A. epos overwinters in a variety of woody trees and shrubs commonly found in woodlots adjacent to vineyards.
Emergence of A. epos and movement into vineyards occurs around the onset of oviposition by grape leafhoppers. The parasite then passes through four to five generations in the vineyard, and reproduces much faster than leafhoppers. Our studies at Dresden and other vineyards suggest that the rate of parasitism increases from <10% of first-brood eggs to 85-90% of second-brood eggs, effectively stopping population growth by mid-season. Data generated by this project will be useful in devising management strategies for conservation and enhancement of biological control by this parasitoid.
An infestation of grape rootworm Fidia viticida, appeared in the Concord blocks in 1993 and continued to be present in 1994. It may have been a contributing factor to yield declines observed in both the organic and conventional Concord blocks in 1994. Because the larval stage is a root-feeding insect, infestations of grape rootworm can severely impact vineyard productivity. In conventional vineyards, insecticide sprays targeted at adults in late June, when they are feeding on grape foliage, are effective in preventing oviposition and subsequent larval infestations. No alternatives for controlling this insect organically are currently available, to our knowledge. Infestations of grape rootworm may therefore be a limiting factor for organic grape production at certain sites.
Fruit , juice and wine quality
Comparison of the juices and wines from the years 1990 to 1994 showed no general difference in the quality (composition) based on the different farming practices. Where small differences in delayed or earlier maturity and in some wine flavor characteristics were apparent the difference was explained by management practices which are not necessarily a consequence of the farming method. For example when a advanced maturity was apparent in the grapes from one treatment this was due to an imbalance in the crop size to the vine size.
During this five-year transition, the organically farmed vines did show some imbalance in vegetative growth and nutrient status which can be expected to be equilibrated after the transition period. Such imbalance can lead to small crops which will be ripened earlier or it can lead to insufficient vine size which is not able to ripen even the smaller crop. On the other hand the larger vine size on the conventionally farmed block can tempt the grower to leave a larger crop which the vines can ripen only more slowly and perhaps not to the same degree.
In some cases differences in juice and wine quality were due to insufficient control of fungal disease and resulting secondary yeast and bacterial infection of the fruit. It appears that in most years these infections can be managed by both growing systems. If in some years this can not be done, a more stringent selection of non-infected fruit in the vineyard or in the winery is necessary to obtain good juice and wine quality. This can add significant costs. It would not allow machine harvest and it would add extra cost with the extra time needed to sort the fruit.
One trend that was apparent in several years was that the sole reliance on copper and sulfur to control fungal pathogens in the organic growing system did lead to significantly higher residual contents of copper in the juice and in the wine. Although in almost all cases the residual copper content in the finished wines after clarification below the legal limit of 0.4 mg/L, in a few individual lots it did exceed this limit. There is no legal limit for copper residue in juice. It is important to watch increased copper residues in juice and wine due to increased reliance on copper as fungicide. No effect on the fermentations was noticed from the increased sulfur applications on the organically grown grapes.
Information gained during this project has been disseminated through cooperative extension and journal publications, symposiums, public and academic lectures, vineyard tours, cooperative extension presentations, and an annual field day for viticulturists. A comprehensive listing of activities and specific publications are listed in Objective 8 - Extension Components - of the accompanying Annual Report. See Attachment I for copies of publications for 1994. In March 1995 a Symposium with published proceedings is planned to share the information gathered during this five-year period. Presentations will include speakers from Germany, Japan, California and New York. A copy of the Symposium brochure with agenda is included.
Impacts of Results/Outcomes
When this project was initiated, perception of growers, researchers and extension agents was that commercial organic production of grape in non-desert climates was not feasible. This project has attempted to apply a combination of traditional and innovative organically acceptable production techniques to commercial vineyards in New York state to establish the commercial feasibility of the system. The result has been the identification of elements which work well, application and refinement of new approaches and the identification of factors which tend to limit complete adoption of an organic production system. Highlights of elements which can be or are being adopted by growers include:
1. Reduction in reliance on insecticides to suppress insect feeding injury We have shown that a combination of pheromone disruption and insect scouting can eliminate the need for scheduled prophylactic use of insecticides in New York vineyards. Pheromones have successfully controlled the primary insect pest, grape berry moth, and scouting has allowed identification of specific pest problems which emerge when prophylactic sprays are eliminated. To date. less than one spray of an organically acceptable insecticide has been required per year. The feared increase in populations of grape leaf hopper has been avoided by encouraging the predatory wasp, Anagrus epos which parasites leaf hopper eggs and appears to maintain leaf hopper populations below the economic threshold levels. Studies on A. epos biology continue. Previously Cornell recommendations were for a minimum of three insecticide sprays per year which is equivalent to 180 tons of carbaryl applied to the state's vineyards. These sprays are essentially eliminated under our management program.
2. Conservation of soil resources and reduction in reliance on herbicides Grapes are a hillside crop which do not tolerate excessive competition from other plants. Traditional deep cultivation and clean covers resulted in so much erosion that grape culture became unprofitable in some production regions. Our goal has been to design sustainable vineyard floor management systems which do not require cultivation and which minimize the need for synthetic herbicides. Presently about 1 ton of the restricted use herbicide, paraquat, is applied to New York vineyards each year. Propane weed burning offers the potential to eliminate the need for this herbicide to control weeds and grapevine suckers. Cover crop systems which utilize natural weed control agents offer the potential to eliminate herbicide use for 20,000 acres of New York vineyards (2/3 of the vineyard area in New York is the between-the-row area suitable for cover crops).
3. Use of bio-control agents or dormant season control strategies to reduce the need for fungicides. We have shown that dormant season control of powdery mildew can essentially eliminate the need for fungicide application to control powdery mildew on moderately resistant varieties (about 90% of the state's 35,000 acres). Use of bio-control agents or dormant eradicants for black rot offer the potential to further reduce the need for chemical fungicides.
4. Reduced need for chemical fertilizers and need for alternate disposal of manures produced by New York farms. Typically grape farms receive 100 lbs of N/acre/year. Currently, many dairy farms in New York state have a problem disposing of all the animal waste they produce in a year. We have shown that animal manures can supply the nitrogen needed in by the state's vineyards.
The results of this five-year study suggest that grapes can be successfully grown using organic management practices, although at a higher cost than is necessary for conventional management systems. Growing costs were from 69 to 91 percent higher, depending upon variety. Yield per acre for the organic system compared to the conventional system over the five years was 22 percent lower for the Concord variety, five percent lower for the Elvira variety, and 35 percent lower for the Seyval Blanc variety. The incidence of higher costs and lower returns meant that returns to management (a measure of profitability) were significantly lower for the organic management practices for all three varieties. The most favorable economic results were obtained for the organic management practices employed with the Elvira vineyard, which showed a small positive profit on average.
The results point out the importance of herbicides in growing grapes using conventional management practices. Conversely, the results indicate the difficulty of viticulture without herbicides, resulting in a high cost of labor and machinery for the eight machine operations and the hand hoeing that is necessary for weed control in organic grape production. Negative results are exacerbated by the lower yields obtained from the additional competition from weeds and possibly from soil compaction as well.
Growers who are considering growing grapes organically should carefully consider the potential costs and returns. Receipts and expenses for a typical growing season were presented to aid interested growers in planning organic production.
A key to economic success with organic production will be whether or not a premium can be realized for organic wine. A survey of growers and vintners conducted five years ago suggested that a price premium was not being realized at that time. However, some vintners in selected markets may be able to sell for a premium over conventional wine. Vintners who are selling wine direct to consumers where the market area is characterized by a relatively high proportion of higher educated and higher income consumers would have the best opportunity to realize a price premium for organic wine.
Changes in Practice
Separate elements of the overall program have been adopted to a greater or lesser extent. Use of the risk assessment protocols to decide about the need for insecticidal control of grape berry moth is widely adopted. Pheromone ties are used extensively, although subsidies from the manufacturer is an important element of acceptance. Other elements of this project have been adopted by extension agents and highlighted in their own programs. Important demonstration plots utilizing elements of these programs have been established in the major grape production regions of the state as educational tools to encourage implementation.
New recommendations which are ready to be implemented include the replacement of chemical fertilizers with manures, and use of propane weed burners as a substitute for paraquat. In more limited circumstances we would alter our present floor management recommendations to reflect understanding gained from this study. In general, farmers should stop routine applications of insecticides and use of certain highly toxic herbicides, and attempt to locate sources of manure to satisfy the grapevine's need for additional nitrogen.
Number of growers/producers in attendance at:
_190 Field Days
_ 45 Vineyard Tours
Areas needing additional study
Currently being investigated are the hypotheses that steam or hot air can be used to eradicate overwintering disease in vineyards, that allelopathic agents produced by decaying rye will sufficiently suppress weed growth to eliminate the need for summer herbicide application and that a natural fungal isolate may suppress or control the development of downy mildew in vineyards.
It is apparent that the primary reason for lower yields in organic vineyards is water relations during dry seasons. Current floor management research indicates that new strategies may partially reduce the excessive competition from non-grape plants growing in organic vineyards, but two alternative methods to improve vine water relations should be added to the study. These are the use of rootstocks to increase the competitiveness of grapevines in relation to alternate floor covers and the use of supplemental irrigation to satisfy both the needs of the vines and floor cover plants required for sustainable production. Additional work is needed to improve the weed burner and demonstrate the extent to which it can replace cultivation or chemical weed control, and the extent to which it can also reduce overwintering disease.
Detailed knowledge of the biology of Anagrus wasps and refined economic thresholds for grape leafhoppers will be required to eliminate the present perceived need by industry for chemical control of the insect. Strategies to manage grape rootworm will have to be developed if a non-chemical control of this potentially devastating insect is to be identified. Continued study of methods to eliminate overwintering fungi growing on grapevines is needed, and further information on biology and use of bio-control agents to control grape fungal disease is required.