- Research Note -
SUSTAINABLE VITICULTURE PRACTICES IN THE SAN JOAQUIN VALLEY OF CALIFORNIA
by
Mark A. Mayse, R. Keith Striegler, William A. O'Keefe,
Vidal A. Perez-Munoz, Fidel R. Garciaand Mbah S. Njokom
CATI Publication #951201
© Copyright December 1995, all rights reserved
ABSTRACT
Interest in developing more sustainable viticulture practices is increasing among growers, consumers, and policymakers. A three-year study (1990-92) was conducted in western Fresno County to investigate the effects of cover crops, nitrogen fertilization, and leaf removal not only on yield and quality parameters, but also on population patterns of arthropod pests and their natural enemies. Viticultural data collected included yield, cluster weight, clusters per vine, berry weight, berries per cluster, percentage bunch rot, pruning weight, soluble solids, pH, titratable acidity, and a series of nutrient levels (NO3-N, K, P, Zn, Mn, Na, Mg, B). Integrated pest management data collected included leaf sampling for leafhoppers and their egg parasitoids and canopy shakecloth sampling for spiders, as well as sweepnet and pitfall trap sampling for herbivores and natural enemies on vineyard floor vegetation. Results confirm that grape growers have effective alternative practices which should be helpful in developing more sustainable viticulture systems.
LITERATURE REVIEW
Cultural practices in vineyards are currently undergoing significant changes. This is due to the growing realization by consumers, growers, and policy makers that conventional viticultural practices may be non-sustainable and contribute to environmental degradation. Some problems which have been associated with conventional viticulture are 1) pest resistance to pesticides and potential residues on grapes; 2) soil compaction; 3) poor water infiltration; 4) soil erosion; 5) low organic matter in the soil; 6) excessive water use; and 7) excessive nitrogen fertilization and nitrate leaching. The severity of these problems may be reduced with use of sustainable viticulture practices such as between vine row cover crops, optimal fertilization and leaf removal (Beall et al. 1991, Barnett 1986, Roy 1991, Garcia 1993, Gubler et al. 1987, Stapleton et al. 1990, Lanini et al. 1988, Ludvigsen 1987, O'Keefe 1993, Perez-Munoz 1993, Pool et al 1990).
Biodiversity and Cover Crops
Monoculture cropping systems are characterized by a lack of stability due to their inherent ecological simplicity (Tedders 1983). Weed-free vineyards may suffer greater insect pest problems according to many European practitioners of integrated pest management (IPM) (Robinson 1987). Selected resident vegetation types, or "weeds," with their nectar, pollen, shelter and moisture have been recognized for their attraction of beneficial arthropods in agroecosystems (Altieri 1981, Bugg et al. 1987). Clear patterns were found for increased presence of spider and parasitic wasp (Anagrus) populations on vines adjacent to cover crops in vineyard ecosystems in the Central Valley (O'Keefe 1993, Garcia 1993). Yet Zalom and Hanna (1992) found that leafhopper population densities and seasonal patterns varied between test vineyards, both of which had cover crops. A faunistic survey of both vineyards and orchards suggested lower insect pest populations and higher beneficial arthropod populations with cover crops when compared to clean cultivation (Altieri and Schmidt 1985).
Biodiversity and Cover Crops
Monoculture cropping systems are characterized by a lack of stability due to their inherent ecological simplicity (Tedders 1983). Weed-free vineyards may suffer greater insect pest problems according to many European practitioners of integrated pest management (IPM) (Robinson 1987). Selected resident vegetation types, or "weeds," with their nectar, pollen, shelter and moisture have been recognized for their attraction of beneficial arthropods in agroecosystems (Altieri 1981, Bugg et al. 1987). Clear patterns were found for increased presence of spider and parasitic wasp (Anagrus) populations on vines adjacent to cover crops in vineyard ecosystems in the Central Valley (O'Keefe 1993, Garcia 1993). Yet Zalom and Hanna (1992) found that leafhopper population densities and seasonal patterns varied between test vineyards, both of which had cover crops. A faunistic survey of both vineyards and orchards suggested lower insect pest populations and higher beneficial arthropod populations with cover crops when compared to clean cultivation (Altieri and Schmidt 1985).
Nitrogen Fertilizer and Grape Physiology
Excessive nitrogen fertilization often results in vigorous canopy development, lower soil pH, higher nitrogen content in must and increased incidence and severity of the bunch rot pathogen complex (Arden-Clarke and Hodges 1988, Conradie and Saayman 1989, Conradie and Saayman 1989, Perret 1986, Smart 1991). In addition, high nitrogen fertilization rates have been positively correlated with increased incidence of Phomopsis viticola infection within grape clusters (Kast 1991). Fortunately for California grape growers, Phomopsis is not considered a problem on the clusters. Excessive nitrogen fertilization reduces fruit color, delays maturity and increases both arginine and total free amino acids (Kliewer 1977). Even though nitrogen is typically applied in vineyards, grapevine requirements are relatively low when compared to other crops such as citrus and corn (Ingels 1990, McCracken 1989, Smith et al. 1986, Winkler et al. 1974).
Nitrogen Fertilizer and Insect Population Densities
Nitrogen is often the limiting nutrient in the growth of both plants and insects (Price 1984). All insects require a protein/amino acid source for growth, synthesis of tissues, and energy production (Hagen et al. 1984). Seventy-five percent of studies reviewed by Jansson et al. (1991) demonstrated increased insect herbivore fitness (i.e., ability to produce viable progeny) as plant nutrition improved. Some amino acids had phagostimulatory effects on pea aphids while others were strong deterrents. Changes in levels of other compounds including hormones and allelochemicals illicit varying responses in phytophagous insect and plant pathogen populations (Risebrow and Dixon 1987). The nutritional status of grapevines in the San Joaquin Valley has been shown to influence the density of variegated leafhopper nymphs (Erythroneura variabilis) (Mayse et al. 1991).
Leaf Removal and Grape Physiology
When leaves are removed from the base of shoots, grapevine canopy microclimate is modified (English et al. 1990, Zoecklein et al. 1992). Radiation levels and evaporation rates within the canopy increase. Consequently, the incidence and severity of grape fungal diseases is reduced by leaf removal (Bettiga et al. 1989, Chellemi et al. 1992, Gubler et al. 1987, English et al. 1990, English et al. 1989, Hunter and Visser 1988, Hunter and Visser 1990, Zoecklein et al. 1992). Composition of wine grapes improved with leaf removal under conventional production practices (Bledsoe et al. 1988, Chellemi et al. 1992, Gubler et al. 1987, Hunter et al. 1991). Advanced maturity and improved color were associated with leaf removal. In addition, leaf removal has been shown to influence vine yield (Candolfi-Vasconcelos and Koblet. 1990). The first year of leaf removal increased soluble solids with no loss in yield; while in the second year soluble solids remained the same and yield declined. The recommended time for leaf removal in California vineyards is two to three weeks post-bloom (Stapleton et al. 1990). This was the same timing used by Candolfi-Vasconcelos and Koblet (1990).
STUDY AREA AND METHODS
This study was conducted in a 10-acre section of a 75-acre flood irrigated, bilateral cordon-trained, spur-pruned, 13-year-old Chenin blanc vineyard near Mendota, California. Vineyard spacing was 7 X 12 feet (vine x row). Row direction was east-west. A T-type trellis was used which had a cordon wire with a one foot cross arm and three catch wires. The soil series was a Panoche silty clay loam. Vines in the study plots were not treated with insecticides or herbicides, but were treated with sulfur for powdery mildew control.
The entire experimental plot was fertilized with 120 lbs of nitrogen per acre (360 kg of nitrogen per hectare) as UAN-32 (32% nitrogen as urea-ammonium nitrate) in 1990. In 1991 and 1992 there were two fertilizer treatments: no nitrogen fertilization and 40 lbs N/A (120 kg N/ha) as UAN-32. Fertilizer was shanked in about two inches deep along rows during all years of this research. Extra water was applied to the research plot (2 furrows / row) when compared to the surrounding production vineyards (1 furrow / row) to maintain the cover crops (see below) in good condition.
Cover crop treatments were initially planted in December 1989 and included a legume mix (Germain's seeds: trefoil, sweet alyssum, poppy and strawberry/white clovers), a grass mix (Germain's companion mix: 80% elka perennial rye and 20% ensylva red fescue), and a cultivated control. Cover crops were replanted in October 1990 because a better stand was desired. Resident vegetation in the cultivated plots was disked two to four times during each season. The cover crop treatments were arranged in a randomized complete block design and the data were analyzed as a factorial. Analysis of variance tests were conducted with means separated by Duncan's multiple range test at the five-percent level.
Viticulture Study
This portion of the study involved three blocks, and the experimental units consisted of approximately 200 vines. Data were collected during the 1990-1992 seasons. Viticultural data (details below) were collected from 10 vines located in the middle of each plot. Three primary factors were evaluated in the viticulture study: nitrogen fertilization, cover crops and leaf removal.
As described earlier, in 1990 the entire experimental plot was fertilized with 120 lbs nitrogen per acre (360 kg N/ha) as UAN-32. Fertilizer was applied post-harvest in 1991 and four weeks after berry set in 1992 because these periods have been shown to have the best assimilation rate in previous studies (Peacock et al. 1991, Peacock et al. 1989).
Leaves were removed two weeks post-bloom, taking them from the base of the shoot to two nodes above the apical cluster. The first season for leaf removal was 1990. Control plots had no leaf removal.
Petiole samples were collected at bloom and pre-harvest in 1990 and 1992, and at bloom time only in 1991 using standard sampling procedures (Christensen et al. 1978). Leaf petioles were dried, ground and analyzed in the laboratory using an Orion ion selective electrode for nitrate- nitrogen (NO3-N). Plasma atomic emission spectroscopy (Perkin-Elmer Plasma 400) was used for the analysis of phosphorus (P), potassium (K), sodium (Na), magnesium (Mg), manganese (Mn), zinc (Zn) and boron (B) from one g of dried and ground grape petiole tissue.
Two hundred berries were collected from the apex of basal clusters on count shoots one day before harvest. The juice from the berries was strained through cheesecloth and analyzed in the laboratory for soluble solids (Abbe refractometer, American Optical model 10450), pH (Beckman pH meter model I70) (Zoecklein et al. 1990). Potassium was analyzed in the juice in 1992 with a Perkin-Elmer atomic absorption spectrophotometer model 2380 (Zoecklein et al. 1990).
At harvest, the number of rotten clusters (summer bunch rot complex) was counted, then weighed and separated from the sound fruit for determination of percent bunch rot. Clusters were considered rotten when 50 percent or more of the cluster had rot as determined by visual inspection. Yield of sound fruit and yield components were also determined. Pruning weights were measured in December of each season.
Pest Management Study
Treatment plots were 40 vines in length down a vine row and six vine rows wide. There were six treatment combinations (cover crop and nitrogen fertilization) and four blocks for a total of 24 treatment plots. Sample rows were designated as one vineyard row north of the center row of each treatment plot.
Leafhopper nymphs were counted on the north side of vine rows once a week for the duration of their presence in the vineyard in 1990. In 1991 six leaves were randomly selected from the inner leaves for the first generation and from the outer leaves for subsequent generations. The number of leafhopper nymphs was recorded according to species [i.e., western grape leafhopper (WGLH) Erythroneura elegantula and variegated leafhopper (VLH) E. variabilis] and age class. Age classes were grouped as first (first instar), small (second and third instar) and large (fourth and fifth instar).
Four studies of leafhopper egg parasitism by the tiny mymarid wasp Anagrus were conducted in 1990 (May 4, June 28, July 27, and August 9). Twenty leaves were collected from the mid-canopy region of the sample row of each legume and cultivated treatment plot. Percent parasitism determinations among treatments were based on careful leaf examination using a dissecting microscope to evaluate leafhopper eggs for the presence of parasitoids.
Within the same general area of the experimental cover crop centers (i.e., 250 yards by 40 yards), arthropods were sampled in midrows by sweepnet and pitfall trap in 1990. This part of the project involved 24 plots: eight replications of two cover crop treatments (grass and legume mixes, species composition described earlier) and a cultivated control. Sweepnet and pitfall sampling alternated throughout the 1990 season with two weekly sweepnet samples to each weekly pitfall sample. A uniform sweeping technique was used, consisting of a three-foot arc sweep and 30 sweeps per plot. Once the sweeps were completed, the net was shaken vigorously to temporarily stun the arthropods. Samples were carefully emptied into plastic bags and labeled as to date and plot.
Two pitfall traps were installed per plot. The traps were harvested and maintained during collection and were capped when sweep sampling occurred. Each pitfall trap consisted of two nested plastic tumblers (six-inch diameter). The outer tumbler served as a soil stabilizer, while the inner tumbler was the actual trap. Each trap held three-to-five inches of antifreeze (ethylene glycol) to kill and preserve the arthropods collected. A six- inch square plywood roof with a four-inch nail in each corner (four nails per roof) covered each trap. The trap cover was pressed down to one inch above the soil and trap level to minimize the collection of insect fliers, mice and toads. When the samples were harvested, the weekly catch was poured through a small sieve (tea strainer), catching the samples, and the antifreeze was returned to the trap. The samples of both sweepnet and pitfall trap were placed in a plastic bag and labeled with the date and plot for identification and tabulation.
Grapevine canopy shake sampling for spiders was conducted seven times during the 1990 season and post-harvest. A two-foot square PVC frame with a muslin cover was used for shake sampling. Five vigorous shakes were made at 30 randomly selected vineyard sampling sites. The spider samples were either tabulated immediately (with early season juvenile spiders) or captured in a plastic bag and labeled with date and vineyard site for identification and tabulation (with adult spider samples later in the season).
RESULTS AND DISCUSSION
Viticulture Study
Growth and Productivity
In 1991, grass cover crop plots had lower pruning weights compared with control and legume plots (Table 1). During 1992, grass continued to reduce pruning weight and also negatively impacted yield. In addition, there were fewer clusters on vines in grass plots than in control plots in 1992. Nitrogen fertilization did not have a significant effect on growth and productivity in 1991 or 1992 (Table 2).
Leaf removal had considerable influence on vine growth and productivity (Table 3). In agreement with prior studies (Bettiga et al. 1989, Gubler et al. 1987, Koblet 1987, Stapleton et al. 1990, Zoecklein et al. 1992), leaf removal lowered the incidence of bunch rot in each year of the study. Leaf removal also reduced pruning weight, cluster weight, and berries/cluster in 1991. Although the number of clusters per vine increased somewhat. During the 1992 season, leaf removal again had significant effects on growth and productivity: yield, pruning weight, cluster weight, and berries/cluster were all lower in leaf removal plots than in control plots. A reduction in yield resulting from leaf removal was previously reported by Candolfi-Vasconcelos and Koblet (1990).
Fruit Composition
Small but consistent treatment effects on fruit composition were detected (Table 4). Fruit composition was not affected by cover crop treatment in 1990. Titratable acidity was higher in legume covers than in the control or grass covers for two consecutive years (1991, 1992). Nitrogen fertilization had little impact on fruit composition. Soluble solids were significantly lower for fertilized plots when compared to non-fertilized plots in 1992. High levels of nitrogen in the soil have been shown to delay and reduce fruit maturation (Kliewer 1977, Winkler et al. 1974).
Leaf removal did not have a significant effect on fruit composition in 1990 (Table 4). In 1991, pH was higher in leaf removal treatments than in the control. Titratable acidity and potassium in juice were reduced by leaf removal. These results are consistent with data reported in previous studies (Wolf et al. 1986, Bledsoe et al. 1988). The reduction in titratable acidity was possibly due to the reduction in potassium content of juice.
Cover Crops and Petiole Nutrient Content
There were no significant differences in bloom petiole nutrient content among cover crops in 1990 (Table 5). In contrast, pre-harvest petioles from control and legume plots had elevated nitrogen content when compared to petioles from grass plots. The bloom nitrogen content during 1991 was significantly higher in the control then in the grass cover crop. Grass produced higher levels of manganese in petioles than did legume and control treatments. This phenomenon may be due to cover crop induced changes in soil pH (McVay 1989) or redistribution of nutrients in the soil profile by cover crops (Gelthin-Jones 1942, Warren et al. 1987).
In 1992, grass and legume cover crops reduced potassium levels at bloom compared to the control. The content of manganese in petioles was increased by the use of grass cover crop, while the magnesium content of petioles was reduced by use of legume cover crop.
Petioles collected at pre-harvest in 1992 displayed important responses to treatment. Nitrate-nitrogen levels were significantly lower for the grass treatment than for control and legume treatments. As previously noted, grass cover crop increased the manganese content of petioles. Also, legume cover crop produced significantly lower sodium than grass cover crop or cultivated control at pre harvest in 1992.
Nitrogen Fertilizer and Petiole Nutrient Content
In 1991, petiole nutrient content levels differed very little in fertilized and unfertilized plots (Table 6). Since fertilizer applications were not made until after harvest during that year, the statistically significant differences in NO3-N levels probably resulted from background differences among experimental plots. In 1992, nitrogen content increased while potassium and magnesium content decreased in bloom petioles from vines which received nitrogen fertilization. These results occurred before the 1992 fertilizer application. Pre-harvest petioles from plots with nitrogen fertilization displayed increased levels of nitrogen and decreased levels of manganese.
Leaf Removal and Petiole Nutrient Content
Leaf removal did not significantly affect bloom petiole nutrient content in 1991 (Table 7). Little effect was seen again during 1992 with the exception of boron, which was at lower levels at bloom in vines with leaf removal. Leaf removal had no effect on petiole nutrient content during the pre-harvest period.
Cover Crop and Fertilizer Interactions
An examination of the interaction between cover crop and nitrogen fertilizer in 1992 revealed some interesting results. Nitrate-nitrogen levels in petioles at pre harvest were substantially higher than at bloom, even for non-fertilized treatments (Table 8). This suggests that the nitrogen found in the petioles of non-fertilized vines came from stored reserves (including from 1990 fertilization), irrigation water and/or soil mineralization.
These data also show that no competition existed for nitrogen from the cover crops in the non-fertilized treatments, and suggests that the reduction in growth (pruning weights) and yield from vines with grass cover crops without fertilization was possibly due to allelopathy. The grass cover crop competed with the vine for nitrogen only if the nitrogen was available; in other words, when the vines were fertilized. Nitrogen fertilizer has been known to compensate for reduced nitrogen availability due to ryegrass competition (Tan and Crabtree 1990).
A reduction in vine growth and yield due to cover crop competition for water was not measured in this study. A measurement of vine water relations could have described this competition for water. Atkinson and Thomas (1985) showed that water consumption was greater when cover crops were planted within fruit orchards.
Pest Management Study
Leafhopper Population Dynamics and Parasitism
In 1990, peak nymph densities occurred in the first generation (Figure 1). Cover crop treatments were not significantly different. The cultivated treatment showed the numerically highest density, while the legume and grass covers had nearly identical and numerically lower nymph densities.
The numerically lower leafhopper nymph densities in the two cover crop treatments may have related to increased densities of generalist predators found in these covers from the sweepnet study. Some of these predators included spiders found in the canopy by Njokom (1991), along with other natural enemies such as minute pirate bug (Orius) and damsel bugs (Nabis). Parasitism by Anagrus was not a major population suppressing factor until late season (Table 9).
The 1991 nymph densities were numerically reduced for the first generation (Figure 2) when compared to that of 1990 (Figure 1). The second generation nymph densities of 1990 and 1991 were very similar.
Similarities in these population histories may reflect the similarity of needs exhibited by two species occupying the same identical niche, or they also could be a reflection of the overall impact abiotic factors have on leafhopper populations in the Central San Joaquin Valley.
By August, parasitism levels had increased in both treatments, but a larger relative increase was seen in the cultivated treatment. The earlier appearance of higher parasitism levels corresponds to findings that cover crops promote increases in densities of beneficial organisms (Bugg and Wilson 1989; Roltsch et al. in press; Zalom and Hanna 1992). The narrowing differences between the two treatments could be the result of dispersal of increasing Anagrus populations from the legume plots to adjacent plots. Similar results in between-plot dispersal of other arthropods were documented in the sweepnet data.
Sweepnet Samples (1990)
Results of the study investigating legume vs. cover crops for arthropods sampled by sweepnet are summarized in Table 10. Among the beneficial arthropods, damsel bugs (Hemiptera: Nabidae) in the genus Nabis were most abundant in the legume mix. These predators reached peak levels of one per sweep throughout July and most of August. Minute pirate bugs (Hemiptera: Anthocoridae) in the genus Orius were nearly 10 times more abundant in both types of cover crop than in low resident vegetation plots. Orius peaked during July at over 1.2 bugs per sweep. Crab spiders (Araneae: Thomisidae) showed treatment patterns similar to Nabis, with greatest abundance in the legume mix, followed by grass cover plots. These spiders peaked at 0.3 per sweep from early July through August.
Among important herbivorous insects sampled by sweepnet in 1990 (Table 10), leafhoppers (Homoptera: Cicadellidae) were by far most abundant in the grass cover, followed by the legume mix. It should be clearly noted that the key grape pest leafhoppers of Figures 1 and 2 in the genus Erythroneura were extremely uncommon in the cover crop sweep samples. However, the grass-loving leafhoppers sampled by sweepnet peaked throughout July and most of August at over 12 per sweep.
Another herbivorous insect, the false chinch bug, Nysius raphanus, which can occasionally cause vineyard problems through intense foliage feeding, was the most abundant in the legume mix with substantial numbers also detected in grass cover plots (Table 10). Nysius showed a sharp peak of two per sweep in early June, with much lower numbers collected throughout July.
Pitfall Samples (1990)
Pitfall trap sampling results from the 1990 study are summarized in Table 11. Among the beneficial arthropods, micryphantid spiders were more abundant in both the legume mix and the grass covers than in the "no cover" plots. These spiders peaked in mid-June at three per plot, gradually decreasing over the rest of the season.
Although little is currently known about the ecological roles of the minute brown scavenger beetle (Coleoptera: Lathridiidae; probably in the genus Corticaria) in California vineyards, lathridiids are generally regarded as fungal feeders. These tiny beetles were clearly most abundant in the legume mix plots (Table 11), reaching 10 adults per trap in mid-June, five per trap in July, and falling to two per trap by late August.
Important parasitoid wasps (i.e., insects that parasitize other insects) in the superfamilies Chalcidoidea and Proctotrupoidea were most abundant in the legume mix, followed by grass cover crops, with surprisingly high numbers in pitfall traps in low resident vegetation (cultivated) plots (Table 11). These relatively tiny parasitic wasps showed consistent population growth patterns in all three treatments, reaching a peak of 10 per trap in the legume mix during late July.
Another specific group of small parasitoids in the super family Proctotrupoidea, the family Scelionidae, showed no significant cover crop treatment effects (Table 11). However, these fairly common egg parasitoids were not detected until July in 1990. Scelionids peaked at more than five per pitfall trap in late July in grass plots, with abundance delayed until mid-August in legume mix and "no cover" areas.
Leafhoppers (not Erythroneura spp. commonly found in the grapevines) sampled by pitfall trapping (Table 11) were clearly most abundant in legume mix plots, followed by grass covers where numbers were still 10 times higher than in low resident vegetation areas. For each treatment, leafhopper densities were relatively consistent throughout most of the season, with up to 75 leafhoppers per trap found in legume cover plots. The fact that most leafhoppers were found in grass plots with sweepnet sampling (Table 10) probably relates to the different physical strata of the field sampled by these two rather distinct sampling methods.
Shakecloth Samples (1990)
The pattern of spider density in the grapevine canopy was generally similar to those sampled in other Central Valley vineyards during 1990. The predominant spider samples were Clubionidae Family (Trachelas spp., a foliage hunting spider) Agelenidae Family (Hololena spp., a funnel web spider) and Salticidae Family (Metaphidippus, a jumping spider) (Figure 3). Trachelas was generally the predominant spider in the grape canopy. Trachelas and Hololena density averages were higher in July and August than in September and October. Spider counts taken September 3 showed a sharp drop probably due to mechanical grape harvesting on September 2. Mechanical harvesting severely disrupts spider grape canopy habitat.
CONCLUSION
Viticulture Study
Legume and grass cover crops had differential effects on vine performance. Use of these types of cover crops in vineyards will require different management practices. Cover crop effects on petiole nutrient content, productivity and fruit composition which were observed in 1991 were even more pronounced in 1992. Grass cover crops reduced the nitrogen concentration and increased the manganese concentration in petioles during 1992. Pruning weight and yield were reduced by the grass cover crops in 1991 and 1992. Grasses have been shown to suppress vine growth, perhaps due to allelopathy (Esteve 1992). Grass competition for nitrogen could serve as a nitrogen sink to prevent this nutrient from leaching into the water table or as a suppressor of vine growth.
Nitrogen fertilization had no effect on yield and growth in this study. Furthermore, bloom nitrogen as low as 100 ppm seemed to fulfill Chenin blanc requirements for growth, productivity, and fruit maturation. Addition of nitrogen fertilizer increased petiole nitrogen (bloom and pre harvest), lowered bloom potassium and delayed fruit maturation (1992).
Leaf removal consistently reduced bunch rot, but in 1991 and 1992 leaf removal also reduced cluster weight, berry weight and pruning weight. In 1992, juice potassium and yield were lower in plots receiving leaf removal. These results underscore the need to find an optimum time for leaf removal, since the timing of this operation has important implications for vineyard productivity. Leaf removal two or three weeks post-bloom reduced growth and yield in this study.
Pest Management Study
Elevated levels of synthetic nitrogen consistently elevated nitrogen levels within the leaves. In 1991, first generation Erythroneura leafhopper nymph densities were numerically higher within the vines treated with the elevated levels of synthetic nitrogen (i.e., cultivated plots). However, leafhopper nymph densities were generally quite low throughout all study plots.
Anagrus parasitism of leafhopper eggs played a major role in reducing nymph populations, as densities appeared to be enhanced by a legume cover crop. Populations of numerous beneficial arthropods were hosted by this cover crop. As beneficial arthropod populations grew, these natural enemies may have dispersed throughout the research plots. This could relate to the increased parasitism rates in cultivated plots by the last sampling date.
The legume cover crop generally had greater numbers of beneficial arthropods. Nectar from flowers serves as a needed energy source for both insect predators and parasites (Debach and Rosen 1991). Phytophagous insects also tend to increase in numbers with cover crops. Most of the phytophagous insects captured in this study are not considered major vineyard pests. These herbivorous insects attract and support greater beneficial arthropod densities. The false chinch bug (Nysius) can be a vineyard pest, and population densities sometimes increase with certain cover crops. Thus Nysius monitoring should generally accompany cover crop use.
The other beneficial arthropods included in Tables 10 and 11 occasionally have been found in vineyard canopies, potentially aiding biocontrol of vineyard pests. With this in mind, a strong case can be made for the benefits of vineyard mid-row plant diversity. Cultivated plots had only sparse numbers of arthropods and cannot rely upon enhanced numbers of beneficials.
Beneficial arthropods generally increase with greater mid-row plant diversity. Minimal dependence upon insecticides should accompany biodiversity enrichment by plant diversity. Central California vineyards had higher spider densities in canopies of vineyards with minimal insecticide use (Njokom 1991). The spiders found in the grapevine canopy support the trend of naturally occurring insect pest control that is generally found when insecticide use is minimized.
Chenin blanc grapevines were grown successfully for three years without reliance on synthetic fertilizer, insecticides and herbicides. Biological systems have shown great potential for adapting to grower needs. Growers sensitive to sustainable and biologically diverse practices within their agroecosystems can avoid the high input and environmental costs of conventional practices (Pimentel et al. 1992) and can have successful crop production (NRC 1989). Our findings in this study indicate that grape growers have numerous alternative practices which should be considered in developing more sustainable viticulture systems.
ACKNOWLEDGEMENTS
The authors would like to acknowledge the private industry support of the following companies: Pilibos Brothers Ranch for partial funding for the research project; Germain Seeds Inc. for donation of cover crop seeds; and Fresno Equipment Company for use of a grain drill.
LITERATURE CITED
Altieri, M.A. 1981. Weeds that may augment biocontrol of insects. Calif. Agric. 35(5,6): 22-24.
Altieri, M.A., and L. Schmidt. 1985. Cover crop manipulations in northern California orchards and vineyards. Biol. Agric. and Hort. 3: 1-24.
Arden-Clarke, C., and R.D. Hodges. 1988. The environmental effects of conventional and organic/biological farming systems. II. Soil ecology, soil fertility, and nutrient cycles. Biol. Agric. & Hort. 5: 223-287.
Atkinson, D., and C.M.S. Thomas. 1985. The influence of cultural methods on the water relations of fruit trees. Acta Horticulturae 171: 371- 382.
Barnett, W.W. 1986. How vegetation management influences trees and vines. IN: Proceedings of the California Weed Conference. pp. 188-189.
Beall, G.A., C.M. Bruhn, A.L. Cragmill and C.K. Winter. 1991. Pesticides and your food: How safe is "safe"?. California Agriculture 45(4): 4-11.
Bettiga, L.J., W.D. Gubler, J.J. Marois and A.M. Bledsoe. 1989 Integrated control of botrytis bunch rot of grape. California Agriculture 43: 9-11.
Bledsoe, A.M., W.M. Kliewer, and J.J. Marois. 1988. Effects of timing and severity of leaf removal on yield and fruit composition of Sauvignon blanc grapevines. Am. J. Enol. Vitic. 39(1):44-54.
Boller, E.F. 1993. Integrated production in European viticulture. Vitic. Enol. Sci. 48: 158-160.
Bugg, R.L., T. Wilson and L.E. Ehler. 1987. Effect of common knotweed on abundance and efficiency of insect predators of crop pests. Hilgardia 55(7): 44-46.
Bugg, R.L., and L.T. Wilson. 1989. Ammi visagna (L.) Lamark (Apiacea): associated beneficial insects and implications for biological control, with emphasis on the bell-pepper agroecosystem. Biol. Agric. and Hort. 6: 241-268.
Candolfi-Vasconcelos, M.C., and W. Koblet. 1990. Yield, fruit quality, bud fertility and starch reserves of the wood as a function of leaf removal in Vitis vinifera - evidence of compensation and stress recovering. Vitis 29: 199-221.
Chellemi, C.O., and J.J. Marois. 1992. Influence of leaf removal, fungicide applications and fruit maturity on incidence and severity of grape powdery mildew. Am. J. Enol. Vitic. 43(1): 53-57.
Christensen, L.P., A.N. Kasamatis and F.L. Jensen. 1978. Grapevine Nutrition and Fertilization in the San Joaquin Valley. Division of Agricultural Sciences, University of California. Publication 4087.
Conradie, W.J., and D. Saayman. 1989. Effects of long-term nitrogen, phosphorus and potassium fertilization on Chenin blanc vines. II. Leaf analyses and grape composition. Am. J. Enol. Vitic. 40(2): 91-98.
Debach, P., and D. Rosen. 1991. Biocontrol by natural enemies. pp. 52, 287 (2nd Ed.) Cambridge Publishers, New York, NY.
Delas, J., C. Melot, and J.P. Soyer. 1982. Effect of excessive nitrogen fertilizer, rootstock and pruning density on the susceptibility of grapevine cultivar Merlot to Botrytis cinerea. Bull. OEPP 12: 177-182.
English, J.T., A.M. Bledsoe, J.J.Marois and W.M. Kliewer. 1990. Influence of grapevine canopy management on evaporative potential in the fruit zone. Am. J.. Enol. Vitic. 41: 137-141.
English, J.T., C.S. Thomas, J.J.Marois and W.D. Gubler. 1989. Influence of grapevine canopies associated with leaf removal and control of botrytis bunch rot. Phytopathology 79: 395-401.
Esteve, Joan. 1992. Interaction between "Berber" orchard grass and young Cabernet Sauvignon grapevines, M.S. Thesis. California State University, Fresno.
Garcia, F.R., 1993. Effect of cultural practices on Erythroneura leafhoppers on grapes in Central California, M.S. Thesis. California State University, Fresno.
Gethin-Jones, G.H. 1942. The effect of leguminous cover crop in building up soil fertility. The East African Agricultural Journal 8: 48-52.
Gubler, W.D., J.J. Marois, A.M. Bledsoe and L.J. Bettiga. 1987. Control of botrytis bunch rot of grape with canopy management. Plant Disease. 71: 599-601.
Hagen, K.S., R.H. Dadd and J. Reese. 1984. The food of insects. pp. 79-112. IN: Ecological entomology. C.B. Huffaker and R.L. Rabb.(eds.). John Wiley and Sons. New York, N.Y.
Hofmann, U. 1993. The influence of conventional and organic farming system on beneficial arthropods in the canopy. Vitic. Enol. Sci. 48: 165-168.
Hunter, J.J., and J.H. Visser. 1988. The effect of partial defoliation, leaf position and developmental stage of the vine on the photosynthetic activity on Vitis vinifera L. cv Cabernet Sauvignon Grapes. II. S. Afr. J. Enol. Vitic. 9(2): 9-15.
Hunter, J.J., and J.H. Visser. 1990. The effect of partial defoliation on growth characteristics of Vitis vinifera L. cv Cabernet Sauvignon Grapes. I vegetative growth. S. Afr. J. Enol. Vitic. 11(1): 18-25.
Hunter, J.J., O.T. De Villiers and J.E. Watts. 1991. The effect of partial defoliation on quality characteristics of Vitis vinifera L. cv Cabernet Sauvignon Grapes. II. Skin color, skin sugar, and wine quality. Am. J. Enol. Vitic. 42: 13-18.
Ingels, C. 1990. California agriculture and groundwater quality. Components 1: 1-2.
Jansson, R.K., G.L. Leibee, C.S. Sanchez and S.H. Lecrone. 1991. Effects of nitrogen and foliar biomass on population parameters of cabbage insects. Entomol. Exp. Appl. 61: 7-16.
Kast, W.K.. 1991. Effects of nitrogen supply on infection of grapevines by Phomopsis viticola Sac. Vitis 30: 17-23.
Kliewer, W.M. 1977. Influence of temperature, solar radiation, and nitrogen on coloration and composition of Emperor grapes. Am. J. Enol. Vitic. 28: 96-103.
Koblet, W. 1987. Effectiveness of shoot topping and leaf removal as a means of improving quality. Acta Horticulturae 206: 141-156.
Lanini, W.T., J.M. Shibbs and C.E. Elmore. 1988. Orchard floor mulching trials in U.S.A. Lefruit Belge, Third quarter, pp. 228-249.
Ludvigsen, R.K. 1987. Vineyard soil management use of cover crops. The Australian Grapegrower & Winemaker 276: 102-108.
Mayse, M.A., W.J. Roltsch, R.R. Roy and V.E. Petrucci. 1991. Effects of nitrogen fertilizer on population dynamics of leafhoppers on grapes. IN: Proceedings of the International Symposium on Nitrogen in Grapes and Wine. J.M. Rantz (ed.) pp. 295-299. ASEV publication, Davis, CA.
McCracken, D. 1989. Control of nitrate leaching with winter annual cover crops. Soil Science News and Views 10: 1-2.
McVay, K.A. 1989. Winter legume effects on soil properties and nitrogen fertilizer requirements. Soil Sci. Soc. Am. J. 53: 1856-1862.
National Research Council. 1989. Alternative agriculture. National Academy Press, Washington D.C.
Njokom, M.S. 1991. Abundance, distribution and ecological role of spiders as natural enemies in grape agroecosystems. M.S. Thesis, Calif. State Univ., Fresno, CA.
O'Keefe, W.A. 1993. Vineyard cover crops for biodiversity and pest management. M.S. Thesis, Calif. State Univ., Fresno, CA.
Peacock, W.L., L.P. Christensen, D.J. Hirshfeldt, F.E. Broadbent,and R.G. Stevens. 1991. Efficient uptake and utilization of nitrogen in drip- and furrow-irrigated vineyards. IN: Proceedings of the International Symposium on Nitrogen in Grapes and Wine. J.M. Rantz (ed.). pp. 116-119 ASEV publication, Davis, CA.
Peacock, W.L., L.P. Christensen and F.E. Broadbent. 1989. Uptake, storage and utilization of soil-applied nitrogen by Thompson Seedless as effected by time of application. Am. J. Enol. Vitic., 40 (1):16-20.
Perez-Munoz, V.A. 1993. Effect of cover crop, leaf removal, and nitrogen fertilization on petiole nutrient content, growth, productivity, and fruit composition of Chenin Blanc grapevines. M.S. Thesis. Calif. State Univ., Fresno. CA.
Perret, P. 1986. Stickstoffoptimierung in rebanlagen. Schwiezerische Zieschrift fur Obst- und Weinbau 122(24) : 694-698 (abstract only).
Pimentel, D., H. Acquay, M. Biltonen, P. Rice, M. Silva, J. Nelson, V. Lippner, S. Giordano, A. Horowitz and A. D'Amore. 1992. Environmental and economic costs of pesticide use. BioScience 42(10): 758.
Pool, R.M., R.M. Dunst and A.M. Lakso. 1990. Comparison of sod, mulch, cultivation and herbicide floor management practice for grape production in nonirrigated vineyards. J. Am. Soc. Hort. Sci. 115(6): 872-877.
Price, P.W. 1984. The concept of the ecosystem. pp. 19-47. IN: C.B. Huffaker and R.L. Rabb (eds.). Ecological Entomology. John Wiley and Sons. New York, N.Y.
Risebrow, A. and A.F.G. Dixon. 1987. pp. 421-448. IN: Nutritional ecology of insects, mites, spiders and related invertebrates. F. Slansky and J.G. Rodriguez (eds.) John Wiley and Sons. New York, N.Y.
Robinson, D.W. 1987. Developments in weed control in viticulture. IN: Integrated pest management in viticulture. Cavalloro, R. (ed.), Baklema Pub., Rotterdam.
Roltsch, W.R., R. Hanna, H. Shorey, M. Mayse and F. Zalom. Spiders and vineyard habitat relationships in central California. IN: Enhancing natural control of arthropod pests through habitat management. C. Pickett and R. Bugg [eds.] In Press.
Roy, R.R. 1991. Influence of grape fertilization on variegated leafhopper population dynamics. M.S. Thesis, Calif. State Univ., Fresno, CA.
Smart, R.E. 1991. Canopy microclimate implications for nitrogen effects on yield and quality. IN: Proceedings of the International Symposium on Nitrogen in Grapes and Wine. J.M. Rantz (ed.) pp. 90-101. ASEV publication, Davis CA.
Smith, M.S., W.W. Frye and J.J. Varco. 1986. Abatement of nitrate pollution in groundwater and surface runoff from cropland using legume no-till corn. Water Resources Research Institute. University of Kentucky, Lexington, KY. Research Report No. 163.
Stapleton, J.J., W.W. Barnett, J.J. Marois,and W.D. Gubler. 1990. Leaf removal for pest management in wine grapes. California Agriculture 44 (5): 15-17.
Tan, S., and G.D. Crabtree. 1990. Competition between perennial ryegrass sod and Chardonnay wine grapes for mineral nutrients. HortScience 25(5): 533-535.
Tedders, W.L. 1983. Insect management in deciduous orchard ecosystems: habitat manipulations. Environ. Manage. 7(1): 29-34.
Warren, S.J., T.J. Monaco and W.A. Skroch. 1987. Effect of vegetation management of soil nutrients and nutrient content of herbaceous vegetation. J. Am. Soc. Hortic. Sci. 112: 962-968.
Wilson, L.T., M.M. Barnes, D.L. Flaherty, D.L. Andris and G.M. Leavitt. 1992. Variegated Grape Leafhopper IN: Grape pest management. D.L. Flaherty, L.P. Christensen, W.T. Lanini, J.J. Marois, P.A. Phillips, L.T. Wilson (eds.). University of California, Division of Agriculture and Natural Resources. Oakland, CA. Publication 3343.
Winkler, A.J., J.A. Cook, W.M. Kliewer and L.A. Lider. 1974. General Viticulture. pp. 107 University of California Press.
Wolf, T.K., R.M. Pool and L.R. Mattick. 1986. Responses of young Chardonnay grapevines to shoot tipping, ethephon, and basal leaf removal. Am. J. Enol. Vitic. 37(4) : 263-268.
Zalom, F.G., and R. Hanna. 1992. Cover crops reduce spider mites. Grape Grower. pp. 14-17.
Zoecklein, B.W., K.C. Fugelsang, B.H. Gump and F.S. Nury. 1989. Production Wine Analysis (First Edition) Van Nostrand Reinhold, New York.
Zoecklein, B.W, T.K. Wolf, N.W. Duncan, J.M. Judge and M.K Cook. 1992. Effect of fruit zone leaf removal on yield, fruit composition and fruit rot incidence of Chardonnay and White Riesling (Vitis vinifera L.) grapes. Am. J. Enol. Vitic. 43: 139-148.
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