Progress 04/01/99 to 09/30/04
Outputs
Significant accomplishments and findings for five major grape diseases follow. Black rot (Guignardia bidwellii). Demonstrated that (i) Berries are highly susceptible to infection for the first 3 weeks after anthesis, then become highly resistant 1-2 wk (cv. Concord) or 2-4 wk later (Chardonnay, Riesling); primary inoculum typically is expended by 2 wk postbloom; fungicides applied from bloom through 4 wk later typically provide excellent control. (ii) Mummies overwintered within the canopy produce 10- to 20-fold as much inoculum as those on the ground and produce peak levels throughout the period of berry susceptibility; removing mummies from the trellis during dormant pruning aids in disease control. (iii) The DMI fungicide, myclobutanil, provides 10 days of post-infection control on seedling foliage and over 7 days on berries in the field, but provides little protective activity; the QoI fungicide, azoxystrobin, provides good protective activity but poor
post-infection control. Botrytis bunch rot (B. cinerea). Although latent infections can occur during bloom, berries are most susceptible after veraison. Significant disease losses apparently result from extensive secondary spread before harvest, with activated latent infections serving as primary infection foci. Secondary spread is strongly exacerbated by tightly-compacted bunches and less so by high berry N content. The fungicide, cyprodinil, provides post-infection activity and some eradication of latent infections when applied weeks after establishment. Downy mildew (Plasmopara viticola). Showed that P. viticola is a heterothallic fungus. Demonstrated that phosphonates control the disease through a combination of protective, post-infection, and antisporulant activities. Activities can be greatest in leaves near the shoot tips. Phomopsis cane and leaf spot (Ph. viticola). Seasonal inoculum is dispersed from bud break until early postbloom. Inoculum production from dead canes is
60-fold higher than from live canes, emphasizing the value of pruning and sanitation for control. Girdling rachis infections are controlled primarily by fungicide applications during the first 2 weeks after clusters emerge; these sprays also provide significant control of berry infections, suggesting that they can originate through the peduncle. High berry N content increases fruit rot severity. Powdery mildew (Uncinula necator). Atmospheric humidity affects colony expansion, sporulation and conidial germination, with an optimum of RH of approximately 85 percent. Overwintering cleistothecia numbers are proportional to foliar disease severity the previous growing season; they can be reduced by late-season applications of petroleum-derived spray oil, but prophylactic disease control is more effective; minimal spray programs are most effective when cleistothecial levels are low. Applications of monopotassium phosphate salt provide post-infection control but no residual protective
activity. Widespread crop losses resulted from the documented development of quantitative resistance to QoI fungicides in U. necator populations. Significant post-infection activity of sulfur was demonstrated conclusively.
Impacts
Black rot: Data have changed control recommendations in NY and surrounding regions, de-emphasizing early fungicide sprays and instead emphasizing a limited number of applications starting at bloom. They also have quantified the benefits of sanitation in an integrated disease management program. Botrytis: The data have helped to reconcile the debate concerning the relative importance of infections at bloom versus those after veraison. By showing that these represent primary and secondary infections, respectively, and demonstrating the role of cluster architecture in disease spread, we have provided a conceptual framework for the management of this disease. Downy mildew: Phosphonates are relatively inexpensive, toxicologically benign compounds only recently introduced for control of this disease. Prior to our study, their physical mode of action was entirely unknown. These data provide fundamental information on their activity necessary for growers and advisors to deploy
them intelligently. Use was extensive in the eastern US in 2003 and 2004. Phomopsis: The data have identified (i) a brief window during which control of rachis infections can be targeted most effectively and (ii) when sprays on all tissues can be discontinued, due to a depletion of seasonal inoculum. Powdery mildew: Humidity data elucidate the importance of a long-misunderstood environmental influence on disease development. Phosphate salt and sulfur data allow these products to be used more efficiently. Cleistothecia data demonstrate importance of and mechanisms for limiting primary inoculum levels.
Publications
- Hoffman, L. E., Wilcox, W. F., Gadoury, D. M., Seem, R. C., and Riegel., D. G. 2004. Integrated control of grape black rot: Influence of host phenology, inoculum availability, sanitation, and spray timing. Phytopathology 94:641-650.
- Gadoury, D. M., Seem, R. C., MacHardy, W. E., Wilcox, W. F., Rosenberger, D. A., and Stensvand, A. 2004. A comparison of methods used to estimate the maturity and release of ascospores of Venturia inaequalis. Plant Dis. 88:869-874.
- Koeller, W., Wilcox, W. F., and Parker, D. M. 2004. Sensitivity of Venturia inaequalis populations to anilinopyrimidine fungicides and their contribution to scab management in New York. Plant Dis. (in press).
- Pattison, J. A., Wilcox, W. F., and Weber, C. A. 2004. Assessing the resistance of red raspberry (Rubus idaeus L.) genotypes to Phytophthora fragariae var. rubi in hydroponic culture. HortScience 39:1553-1556.
- Turechek, W. T., and Wilcox, W. F. 2004. Evaluating predictors of apple scab with ROC analysis. Phytopathology (in press).
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Progress 01/01/03 to 12/31/03
Outputs
In a Chardonnay vineyard where Uncinula necator resistance was documented in 2002, QoI fungicides provided little to no control of powdery mildew on fruit clusters regardless of rate, but did provide modest control of foliar infections in a rate-dependent manner. Rotational programs that included solo applications of QoIs during the critical early postbloom period also provided very poor control on clusters but did provide good control on leaves, likely due to midsummer rotations with sulfur. Tank-mixing sulfur with QoIs in the early postbloom period improved control on both clusters and foliage, but only modestly. In contrast, a similar program utilizing a commercial mix of a QoI (pyraclostrobin) plus a carboxanilide (boscalid) provided excellent control of foliar infections and relatively good control on clusters; nearly all of this activity was provided by the boscalid component. Solo applications of boscalid were significantly more effective than sulfur for
control of cluster infections. The new quinoline fungicide, quinoxyfen, also provided superior control. Phomopsis viticola produced approximately 100 times as many spores from infection sites in dead versus live canes, vividly illustrating the importance of removing dead wood as part of a Phomopsis management program. On Concord clusters inoculated at the 3 to 5 inch shoot stage, 58 percent of the rachises developed serious girdling infections, but less than 10 percent did so when inoculated 10 days prebloom through fruit set. The suggestion that the early growth period is most critical for fungicidal control of this disease was confirmed through fungicide timing trials. Increasing the postveraison N content of grape berries increased the frequency of active infections (rot) that developed from latent infections of Botrytis cinerea initiated at harvest. Increased N also appeared to increase berry susceptibility to post-veraison disease resulting from berry-to-berry contact or external
air-blown spores. Activation of latent infections was promoted by periods of high humidity during the 10 days before harvest, proportional to the duration of the humid period, whereas similar humid periods at veraison had no effect. Fenhexamid and cyprodinil provided limited but significant postinfection control of latent infections when applied the first few days after floral infection. For pre-infection treatments, both were equally effective whether applied before or after cap fall, suggesting that the pedicel, rather than stamens, may be an important infection court; practically, this suggests an element of flexibility in the timing of such sprays. Phosphorous acid (PA) provided significant protective and postinfection activity against downy mildew. The protective activity declined significantly between 3 and 7 days in the oldest inoculated leaves, although this was compensated by their reduced susceptibility to infection. Sporulation was reduced by 95 to 100 percent on most
leaves in most treatments, and by approximately 85 percent in the others. PA did not eradicate active lesions when diseased leaves were sprayed, but did reduce additional spore production.
Impacts
These results should improve the ability of grape producers to understand and control four major fungal diseases of this crop. The work on powdery mildew provides a further explanation for the unexpected failures to control this disease in 2002 and 2003, and identifies alternative management tools. The work on Phomopsis emphasizes the importance of a cultural control procedure and refines the optimum timing for fungicidal intervention. The Botrytis results provide significant new insight into an important but poorly understood aspect of the biology of this disease, i.e., the activation of latent infections, and also provides practical information relative to fungicidal control of such infections. These are the first reported data concerning the physical mode of action of phosphorous acid against downy mildew. PA is recognized by the EPA as a biopesticide exempt from residue tolerances and is relatively inexpensive; increased knowledge of its activities may lead to
both environmental and economic benefits.
Publications
- Carroll. J. E., and Wilcox, W. F. 2003. Effects of humidity on the development of grapevine powdery mildew. Phytopathology 93: 1137-1144.
- Hoffman, L. E. and Wilcox, W. F. 2003. Factors influencing the efficacy of myclobutanil and azoxystrobin for control of grape black rot. Plant Dis. 87:273-281.
- Gadoury, D. M., Seem, R. C., Ficke, A., and Wilcox, W. F. 2003. Ontogenic resistance to powdery mildew in grape berries. Phytopathology 93:547-555.
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Progress 01/01/02 to 12/31/02
Outputs
Factors affecting the secondary spread of Botrytis bunch rot (BBR) were studied on three grape cultivars. On a naturally tight-clustered clone of cv. Pinot Noir, selected bunches were hand-thinned to provide loose clusters approximating those of the Mariafeld clone; then, either 1, 3, or 5 berries per cluster were inoculated with B. cinerea at veraison to provide initial disease foci. Regardless of the number of inoculation sites, only 3 to 7 uninoculated berries became diseased by harvest in thinned clusters, versus 45 to 50 in unthinned clusters. On cvs. Chardonnay and Riesling, the effect of cluster compactness was examined in combination with four weekly sprays of urea (9kg/ha) starting at veraison. Inoculations were as before. For all treatment combinations on Chardonnay, there was a strong linear relationship (r-squared=0.86 to 0.97) between the number of berries inoculated at veraison and the additional number of diseased berries at harvest. Thinning
dramatically reduced disease spread in all treatment combinations. Urea applications increased disease severity approximately 3-fold when 1 or 3 berries were inoculated in unthinned clusters. A wet preharvest period for late-maturing Riesling led to significant disease development in all treatments. There was a strong (r-squared=0.92 to 0.97) logarithmic relationship between the number of inoculated berries and final disease severity. Under these conditions, the effect of thinning was substantially reduced whereas the detrimental effect of urea applications was more evident. These data confirm that severe BBR is often due to preharvest spread from a few initial foci and that spread is much more pronounced through tight versus loose clusters. They also suggest that berry N content may affect susceptibility to BBR. Fungicide timing trials were conducted on 'Concord' grapevines to determine the optimum period for controlling rachis infections caused by Phomopsis viticola. A mancozeb
spray at the 7- to 13-cm growth stage (when clusters first become visible) appeared to be critical for controlling the most serious infections. A single application at this time provided 88 percent control of infections girdling more than half of the cluster, although additional sprays provided additional control of less-severe infections. In contrast, withholding sprays until the immediate prebloom period provided little to no control of rachis infections. Severe powdery mildew developed in 2002 on the clusters of highly-susceptible cultivars in many regional vineyards where strobilurin fungicides were used during the critical postbloom period. In one replicated trial, azoxystrobin and pyraclostrobin provided little control of such infections, whereas excellent control was provided by a mixture of pyraclostrobin and an unrelated carboxanilide fungicide, or by the carboxanilide alone. Assays of individual U. nector isolates from these plots indicate a directional shift similar to
those conferring practical resistance to DMI fungicides, but provide no evidence of a target-site mutation typically associated with strobilurin resistance in other fungi.
Impacts
These results should allow commercial grape producers to improve the efficiency of their disease management programs. Management of BBR should focus on reducing the number of initial disease foci early in the season plus minimizing disease spread during the preharvest period; non-fungicidal practices that loosen clusters and provide optimal N nutrition should assist with this goal. Rachis infections by P. viticola are perhaps the most costly fungal disease of juice grapes in the Great Lakes region; these results show that serious losses can be minimized with a limited number of fungicide sprays if their timing is optimized. Powdery mildew is the most ubiquitous disease of grapes and commercial production of most varieties is dependent on its control. These are the first results from the United States indicating resistance to the strobilurin fungicides by the causal pathogen. Growers relying upon the strobilurins in their management programs will need to make
appropriate adjustments to avoid further losses in 2003.
Publications
- Hoffman, L. E., Wilcox, W. F., Gadoury, D. M., and Seem, R. C. 2002. The influence of grape berry age on susceptibility to Guignardia bidwellii and its incubation period length. Phytopathology 92:1068-1076.
- Wilcox, W. F. and Latorre, B. L. 2002. Identities and geographic distributions of Phytophthora species causing root rot of red raspberry in Chili. Plant Dis. 86:1357-1362.
- Wong, F. P. and Wilcox, W. F. 2002. Sensitivity to azoxystrobin among isolates of Uncinula necator: Baseline distribution and relationship to myclobutanil sensitivity. Plant Dis.: 86:394-404.
- Zitter, S. M. and Wilcox, W. F. 2002. Early Botrytis infections as sources of secondary inoculum for ripening grape berries. Phytopathology 92:S92 (Abstr.).
- Kennelly, M. M., Seem, R. C., Gadoury, D. M., Wilcox, W. F., and Magarey, P. A. 2002. Refinement of DMCast, a predictor of grapevine downy mildew (Plasmopara viticola). Phytopathology 92:S41 (Abstr.)
- Hoffman, L. E. and Wilcox, W. F. 2002. Utilizing epidemiological investigations to optimize management of grape black rot. Phytopathology 92:676-680.
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Progress 01/01/01 to 12/31/01
Outputs
The DMI fungicide, myclobutanil, provided complete control of black rot (Guignardia biwellii) when applied to grape seedlings up to 6 days after inoculation with 10E4 or 10E6 conidia/ml, whereas control of mean lesion area declined to 91 and 75% following 8- and 10-day postinoculation treatments, respectively. No pycnidia were found in the few lesions that did form in the 8-day postinoculation treatment; similarly, pycnidium formation in lesions that developed after the 10-day postinoculation treatment was reduced by 98%. Azoxystrobin provided significantly less curative control than myclobutanil at the lower inoculum concentration and even less at the higher concentration, but did provide consistent reduction of conidium formation within pycnidia that developed in resultant lesions. When assayed on leaf discs treated with 20 mg/L azoxystrobin, conidium germination was inhibited by 43 to 85% for the five G. bidwellii isolates tested, but was inhibited by >99% when
inoculum droplets were amended with SHAM (an inhibitor of alternative respiration). Similarly, appressorium formation was inhibited by 68-93% when unamended droplets were inoculated onto treated leaf discs, whereas no appressoria formed when SHAM was included in the inoculum. These data, and similar results from related tests on intact seedlings, indicate that some conidia of G. bidwellii can utilize alternative respiration to germinate, form appressoria, and establish latent infections on grape leaves when treated with commercial rates of a strobilurin fungicide. Berries on a tight- and loose-clustered clone of Pinot Noir (PN29 and Mariafeld, respectively) were inoculated with Botrytis cinerea at late bloom through veraison; also inoculated were PN29 clusters which had been thinned to approximate the looseness of Mariafeld. The incidence of latent infection was comparable among all three clonal treatments at each of four inoculation times. However, for each of the four inoculations,
disease at harvest was significantly higher in the unthinned clusters of PN29 than in the thinned clusters of this clone or Mariafeld. Virtually no disease developed on thinned PN29 or Mariafeld when clusters were inoculated through bunch closure (verus up to 15% for unthinned PN29). Inoculations at veraison produced significantly more disease than did inoculations at any other time, i.e., 6, 16, and 41% for Mariafeld, thinned-, and unthinned PN29, respectively. When 0-5 Chardonnay berries per cluster were injected with B. cinerea spores to induce point sources of secondary inoculum 2 wk before harvest, there was a strong linear relationship between the number of inoculated berries and subsequent disease spread (10, 24, and 40% infection following inoculation of 1, 3 and 5 berries per cluster, respectively). Thus, the establishment of only a few early infections can lead to significant spread as berries ripen. The pattern of spore release for Phomopsis viticola showed a similar
pattern in two different vineyards; a gradual build-up to a sharp peak of release near bloom, with a sharp drop-off through midsummer.
Impacts
Strobilurins are a new group of fungicides generally classified as "reduced risk" compounds by the US-EPA; the results of this research provide new information pertaining to their most-efficient use in disease management programs for grapes. Botrytis bunch rot is one of the most serious but least-understood fungal diseases of wine and table grapes. The results of this research provide new insights into the role of cluster architecture on disease development and the relative consequences of infection events at different stages of crop development; such information should improve integrated pest management programs by identifying a potential non-chemical control component (cluster thinning) in addition to the best timings for fungicide applications.
Publications
- Dalbo, M.A., Ye, G.N., Weeden, N.F., Wilcox, W.F., and Reisch, B.I., 2001. Marker-assisted selection for powdery mildew resistance in grapes. J. American Society of Hort Science 126:83-89.
- Gadoury, D.M., Seem, R.C., Pearson, R.C., Wilcox, W.F., and Dunst, R.M., 2001. Effects of powdery mildew on vine growth, yield, and quality of Concord grapes. Plant Dis. 85:137-140.
- Koeller, W., and Wilcox, W.F., 2001. Evidence of predisposition of fungicide-resistant isolates of Venturia inaequalis to a preferential selection for resistance to other fungicides. Phytopathology 91:776-781.
- Latorre, B.A., Rioja, M.E., and Wilcox, W.F., 2001. Phytophthora species associated with root and crown rot of apples in Chile. Plant Dis. 85:603-606.
- Wong, F.P., Burr, H.N., and Wilcox, W.F., 2001. Heterothallism in Plasmopara viticola. Plant Pathol. 50:427-452.
- Wong, F.P., and Wilcox, W.F., 2001. Comparative physical mode of action of axoxystrobin, mancozeb, and metalaxyl against Plasmpara viticola (grapevine downy mildew). Plant Dis. 85:649-656.
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Progress 01/01/00 to 12/31/00
Outputs
The relationship between sensitivity of the grape powdery mildew (PM) fungus (Uncinula necator) to azoxystrobin (azx)and myclobutanil (myc) was compared at a vineyard with no history of synthetic fungicide use versus one where control of PM with myc and similar fungicides has been compromised by resistance. The U. necator isolates most resistant to myc also were least sensitive to azx, although the range in sensitivities (lowest-highest ED50 values) was much greater for the former (approx. 740- vs. 22-fold, respectively). When grape seedlings were sprayed with various azx rates 1 day before or 5 days after inoculation with subpopulations of U. necator most and least sensitive to the fungicide, only postinfection sprays at 0.1x recommended rate selected the less sensitive subpopulation. In controlled tests, relative humidity (RH) had a moderate to pronounced effect on PM severity, e.g., leaf area infected increased approximately 2- to 5-fold as RH increased from 39 to
98% in different experiments. The frequency of spore germination and the intensity of spore formation from infected tissue also increased with increasing RH, but more modestly. Monopotassium phosphate, a foliar fertilizer labeled for PM control, provided no protective activity when grape cuttings were sprayed 1-7 days before inoculation, but provided significant control when they were sprayed 3-7 days afterward. Spore formation from surviving colonies also was reduced significantly by postinfection sprays. The influence of variable PM control was examined for 5 yr on Concord vines pruned to provide three different cropping levels. Increasing levels of control provided increasing levels of both sugar production and yield in all three cropping systems, although differences were most pronounced in the highest-yielding treatment. Inoculated Concord fruit were highly susceptible to black rot (Guignardia bidwellii) for the first 4 wk after bloom; disease severity was reduced by 70% for
inoculations made 5 wk postbloom and no disease occurred from those made 6 wk postbloom. Chardonnay and Riesling berries remained highly susceptible through 5 wk postbloom, and retained reduced susceptibility through 7 wk postbloom. Disease progress was completed within 21 days on clusters inoculated near bloom. In contrast, clusters inoculated 6 and 7 wk postbloom showed few symptoms after 21 days; most symptoms developed 23 to 33 days after inoculation. Berries on a tight- and loose-clustered clone of Pinot Noir (PN29 and Mariafeld, respectively) were inoculated with Botrytis cinerea at late bloom through bunch closure (BC); also inoculated were PN29 which had been thinned to approximate the looseness of Mariafeld. Disease severity was 2- to 9 times higher on harvested clusters that had been inoculated from LB to BC than on uninoculated checks, demonstrating the potential effect of early infections. Bunch rot development was appreciably higher on PN29 than on either PN29/thinned or
Mariafeld, which behaved similarly. The documented resistance of Mariafeld appears due to cluster architecture rather than some other factor. Plasmopara viticola (grape downy mildew) was shown to be a heterothallic fungus.
Impacts
(N/A)
Publications
- Hoffman, L.E., Wilcox, W.F., Gadoury, D.M., and Seem, R.C. 2000. Postinfection activities of myclobutanil and azoxystrobin against Guignardia bidwellii. Phytopathology 90:S35 (Abstr.).
- Wong, F.P., Burr, H.N., and Wilcox, W.F. 2000. Heterothallism in Plasmopara viticola (grapevine downy mildew). Phytopathology 90:S85 (Abstr.).
- Gadoury, D.M., Seem, R.C., Ficke, A., Wilcox, W.F. and Henick-Kling, T. 2000. Diffuse infections of Uncinula necator predispose grape berries to bunch rot and spoilage microorganisms, and degrade wine quality. Phytopathology 90:S26 (Abstr.).
- Wong, F.P. and Wilcox, W.F. 2000. Baseline sensitivity of Plasmopara viticola to azoxystrobin. Plant Dis. 84:275-281.
- Wong, F.P. and Wilcox, W.F. 2001. Physical mode of action of azoxystrobin on control of grapevine downy mildew (Plasmopara viticola). Plant Dis. (in press).
- Wong, F.P. and Wilcox, W.F. 2001. Heterothallism in Plasmopara viticola (grapevine downy mildew). Plant Pathol. (in press).
- Koeller, W. and Wilcox, W.F. 2000. Interactive effects of dodine and the DMI fungicide fenarimol in the control of apple scab. Plant Dis. 84:863-870.
- Gadoury, D.M., Seem, R.C., Pearson, R.C., Wilcox, W.F. and Dunst, R.M. 2001. Effects of powdery mildew on vine growth, yield, and quality of Concord grapes. Plant Dis. 85:137-140.
- Dalbo`, M.A., G.N. Ye, N.F. Weeden, W.F. Wilcox, and B.I. Reisch. 2001. Marker-assisted selection for powdery mildew resistance in grapes. J. Amer. Soc. Hort. Sci. 126:83-89.
- Carroll, J.E. and Wilcox, W.F. 2000. The effect of relative humidity on grape powdery mildew development and pathogen sporulation. Phytopathology 90:S12 (Abstr.).
- Wong, F.P., Burr, J.A., Riegel, D.G. and Wilcox, W.F. 2000. Relationship between sensitivities to azoxystrobin and myclobutanil among isolates of Uncinula necator. Phytopathology 90:S85 (Abstr.).
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Progress 01/01/99 to 12/31/99
Outputs
A method was developed for determining baseline sensitivities of the grapevine downy mildew fungus (Plasmopara viticola) to the fungicide, azoxystrobin. Surface-sterilized leaf discs were inoculated with 80 single-sporangiophore isolates of the fungus, using 20 replicate discs per isolate for each fungicide concentration. Measurements of disease incidence and severity 7 days later gave comparable results, although disease incidence measurements were much easier to obtain. There was an approximately 20-fold range in ED (50) values within this baseline population, and all values were less than 1 ppm. In a series of fungicide-timing protocols, grape black rot was controlled completely in a high inoculum vineyard with sprays at prebloom plus 2 and 4 wk later, even though most of the seasonal ascopore load was discharged during six infection periods prior to the first application. Controlled inoculation experiments in other vineyards showed that fruit of four different
grape varieties were highly susceptible during the first 2-3 wk after bloom and became highly resistant by 4-5 wk after bloom. Thus, protection of fruit during their period of highest susceptibility provided optimal disease control, even when early leaf infections were allowed to develop. However, in a vineyard with extreme inoculum carryover, an additional spray applied 2 wk before the prebloom application (i.e., to control leaf infections) provided additional control of fruit infections. In a machine-pruned vineyard with high levels of mummified fruit retained in the canopy, subsequent hand-pruning of mummies to the ground significantly reduced fruit rot severity relative to plots that did not receive this sanitation treatment, e.g., 5 versus 18% infection, respectively, for the most effective fungicide program. Clusters of a tight-clustered Pinot noir clone and those of the loose-clustered 'Mariafeld' clone were inoculated with Botrytis cinerea spores at 90% bloom, pea-sized berry
stage, and veraison. The incidence of latent berry infections was assessed 7, 14, and 21 days after inoculation by killing the tissues with paraquat and determining the incidence of berries on which the fungus was sporulating. The incidence of latent infections was 90 to 100% for inoculated berries of both clones, versus 5 to 15% of berries in the tight-clustered clone developed disease at harvest, whereas less than 2% of berries in the 'Mariafeld' clone became diseased.
Impacts
(N/A)
Publications
- Wong, F. P., and Wilcox, W. F. 2000. Baseline distribution of sensitivities to azoxystrobin among isolates of Plasmopara viticola. Plant Disease (in press).
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