Whole-farm Impact of Converting Conventionally Managed Eastern Vineyards to Organic Management Practices

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.

Floor Management
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

Powdery Mildew
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.

Black Rot
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.

Downy Mildew
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.