Progress 07/15/05 to 07/14/08
Outputs
OUTPUTS: Two growing degree-day models (based upon air and soil temperature) that predict the first emergence of hop shoots systemically infected with the downy mildew pathogen (i.e., primary spikes) were evaluated in small plots and commercial yards of cooperating growers. In hop production regions where downy mildew becomes epidemic annually these models may predict when fungicide applications should begin to protect plants from the early season spread of inoculum from primary basal spikes. Small plots of cultivar Willamette and Nugget were examined three to five times per week beginning from shoot emergence until the first primary spike was observed. Air temperature and soil temperature were collected. Additionally, seven commercial hop yards (four of cultivar Willamette and three of cultivar Nugget) were surveyed two to three times each week beginning on 28 February to detect the appearance of the first primary basal spike. Regional air and soil temperature were obtained from the nearest regional weather. A downy mildew forecast model developed in England (Royal, 1973) was also validated in small plots as described above. When an infection period is predicted to have occurred, a fungicide application is recommended to limit secondary spread of disease. Growers in England following this model often eliminated one fungicide application per season as compared to calendar-based applications, but disease control was improved significantly. The infection risk model was validated in experimental plots. Treatments included untreated, fungicide treatments applied preventatively (standard), and applications timed according to the infection risk forecast. A rotation of fosetyl-Al, cymoxanil and copper hydroxide, and trifloxystrobin and copper hydroxide were applied at the highest rates allowable. Disease severity was assessed by counting the number of primary and secondary basal spikes, in each treated hill every 7 to 14 days beginning in early April. The number of aerial spikes was counted on each plant during the evaluations. At harvest, 50 cones were collected from each plant and examined for infection. The infection risk model was further validated in assays with potted hop indicator plants. Pots of the Nugget variety were deployed for 24 or 48 hr periods to expose the plants to environmental conditions and natural inoculum. Concentration of sporangia in the air was measured with a volumetric air sampler positioned near the trap plants. After the exposure period, the plants where placed in a greenhouse maintained at approximately 25 C for 7 days. Downy mildew infection severity was assessed by counting the number of lesions per leaf area. A total of 28, 59, and 38 sets of plants (data sets) were collected for a 24-hr period in 2005, 2006, and 2007, respectively. A total of 29 and 19 data sets were collected a 48-h period in 2006 and 2007, respectively. Weather and inoculum factors were related to infection severity by regression and nonparametric analyses. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Hop producers and crop consultants are the target audience and information has been partially disseminated through presentations at meetings. More information will be disseminated in workshops and on the web. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The growing degree day model based on air temperature predicted the appearance of basal spikes eight days after the first sporulating spike was observed in experimental plots of cultivar Nugget in Corvallis. In commercial yards, the first sporulating spikes were observed on 24 March in two yards of cultivar Willamette, 12 days before the model predicted. By 31 March, spikes were observed in two other Willamette yards and three yards of cultivar Nugget, 5 days earlier than predicted by the model but still within the expected range. Therefore, the model was late in predicting disease appearance in the experimental plots and two Willamette yards with very low incidence of disease (<1%), but the emergence of basal spikes was predicted within the expected range of the model for five of the commercial yards surveyed. Validation of a downy mildew forecast model that predicts the severity of infection events in response to weather (rainfall and hours of relative humidity about 90% in the previous 48 hr period) is promising. Initiating fungicide applications by the growing degree-day model significantly reduced disease as compared to the standard grower application timing in three of four years. Fungicide applications applied according to only the risk index provided disease suppression equivalent to that of the standard program in three of four years, but with three or four fewer applications during 2005 to 2008. The infection risk model was further validated in assays with potted hop indicator plants. Disease incidence and infection severity on indicator plants varied among days when the plants were placed in the hop yard. For the plants deployed 24-hr, infection occurred on 18 of the 125 days. For the plants deployed 48-hr, infection occurred on 16 of the 48 sets of plants. Discriminate analysis was used to predict for days when disease did or did not develop on the bioassay plants. A quadratic discriminate function was developed for the 24-hr data sets that included the predictors hours of relative humidity >80%, degree-hours of wetness, and mean night temperature. In cross validation, a quadratic discriminate function with these variables classified 88.8% of days into the correct category, with 83.3% sensitivity and 89.0% specificity, assuming a nominal threshold of 0.5 for designating a day as an infection day. For the 48-hr data sets, the final model included predictor variables for hours of relative humidity > 80%, degree-hours of wetness, mean night temperature, and an interaction variable for the product of mean night temperature and hours of relative humidity > 80%. In cross validation, a quadratic discriminate function for the 48-hr data sets had 77.1% accuracy, 68.8% sensitivity, and 81.3% specificity, assuming a nominal threshold of 0.5.
Publications
- No publications reported this period
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Progress 07/15/06 to 07/14/07
Outputs
OUTPUTS: Two growing degree-day models (based upon air and soil temperature) that predict the first emergence of hop shoots systemically infected with the downy mildew pathogen (i.e., primary spikes) were evaluated in small plots and commercial yards of cooperating growers. In hop production regions where downy mildew becomes epidemic annually these models may predict when fungicide applications should begin to protect plants from the early season spread of inoculum from primary basal spikes. Small plots of cultivar Willamette and Nugget were examined three to five times per week beginning from shoot emergence until the first primary spike was observed. Air temperature and soil temperature were collected. Additionally, seven commercial hop yards (four of cultivar Willamette and three of cultivar Nugget) were surveyed two to three times each week beginning on 28 February to detect the appearance of the first primary basal spike. Regional air and soil temperature were obtained from the
nearest regional weather. A downy mildew forecast model developed in England (Royal, 1973) was also validated in small plots as described above. When an infection period is predicted to have occurred, a fungicide application is recommended to limit secondary spread of disease. Growers in England following this model often eliminated one fungicide application per season as compared to calendar-based applications, but disease control was improved significantly. The infection risk model was validated in experimental plots. Treatments included untreated, fungicide treatments applied preventatively (standard), and applications timed according to the infection risk forecast. A rotation of fosetyl-Al, cymoxanil and copper hydroxide, and trifloxystrobin and copper hydroxide were applied at the highest rates allowable. Disease severity was assessed by counting the number of primary and secondary basal spikes, in each treated hill every 7 to 14 days beginning in early April. The number of
aerial spikes was counted on each plant during the evaluations. At harvest, 50 cones were collected from each plant and examined for infection. The infection risk model was further validated in assays with potted hop indicator plants. Ten to 20 pots of the Nugget variety were deployed for 24 or 48 hr periods to expose the plants to environmental conditions and natural inoculum. Concentration of sporangia in the air was measured with a volumetric air sampler positioned near the trap plants. After the exposure period, the plants where placed in a greenhouse maintained at approximately 25 C for 7 days. Downy mildew infection severity was assessed by counting the number of lesions per leaf area. In total, 59 sets of indicator plants were deployed for 24 hr periods over the season from 4 April through 26 October. Another set of 31 plants were deployed for 48 hr periods. Weather and inoculum factors were related to infection severity by regression and nonparametric analyses.
PARTICIPANTS: (PIs/PDs) Cynthia M. Ocamb (Associate Professor and Extension Specialist, Botany and Plant Pathology, Oregon State University) helped in design of the research and assisted with execution of studies on validation of a downy mildew forecast model. David H. Gent (Research Plant Pathologist, USDA-ARS, National Forage Seed Production Research Center, Corvallis, OR), led the design of studies and execution of studies on growing degree-day models, validation of a downy mildew forecast model with potted plants, and data analysis. Technical assistance on growing degree-day models and validation of a downy mildew forecast model was provided by Joanna Woods (formerly Farnsworth).
TARGET AUDIENCES: Information on preliminary research results have been disseminated through grower meetings and research reports to the Hop Research Council.
Impacts
The growing degree day model based on air temperature predicted the appearance of basal spikes eight days after the first sporulating spike was observed in experimental plots of cultivar Nugget in Corvallis. In commercial yards, the first sporulating spikes were observed on 24 March in two yards of cultivar Willamette, 12 days before the model predicted. By 31 March, spikes were observed in two other Willamette yards and three yards of cultivar Nugget, 5 days earlier than predicted by the model but still within the expected range. Therefore, the model was late in predicting disease appearance in the experimental plots and two Willamette yards with very low incidence of disease (<1%), but the emergence of basal spikes was predicted within the expected range of the model for five of the commercial yards surveyed. Validation of a downy mildew forecast model that predicts the severity of infection events in response to weather (rainfall and hours of relative humidity about
90% in the previous 48 hr period) is promising. Fungicide applications applied according to the downy mildew risk index provided disease suppression similar to that of the standard grower spray program, but with four or five fewer applications. The infection risk model was further validated in assays with potted hop indicator plants. Disease incidence and infection severity on indicator plants varied among days when the plants were placed in the hop yard, ranging from 0 to 55 % leaf incidence and 0 to 0.04 lesion/cm2, respectively. Disease was not observed on indicator plants after 17 July, which closely corresponds to the last date when significant airborne inoculum was trapped in the hop yard. Days when 10% or more of the leaves developed downy mildew lesions were arbitrarily classified as major infection events. On six days, major infection events were observed, while minor infection events were observed on two days, and no infection was observed on 50 days. Preliminary analysis of
the weather data suggests that of the weather variables investigated, duration of morning leaf wetness was one of the best predictors of major infection events.
Publications
- No publications reported this period
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Progress 07/15/05 to 07/15/06
Outputs
The overall goal of this research and extension project is to improve hop grower profitability and sustainability with reduced-risk pest management tactics. Two growing degree-day models were evaluated in Oregon fields for prediction of the first emergence of hop shoots systemically infected with the hop downy mildew pathogen (i.e., primary spikes). In 2005, a growing degree day model based on air temperature predicted the emergence of basal spikes in experimental plots of cv. Nugget and two commercial yards of cv. Glacier within three days of the actual emergence. An infection risk index was validated in experimental plots of cv. Nugget and compared with a typical fungicide program for management of downy mildew. Initiating fungicide applications by the growing degree-day model significantly reduced disease as compared to the standard grower application timing. Fungicide applications applied according to the risk index provided disease suppression equivalent to that
of the standard program, but with three fewer applications during 2005. Potted hop plants were also used to quantify weather variables related to infection events. Successive sets of potted plants were deployed in an untreated area of an experimental hop yard for 24 h periods from March through October of 2005. Multivariate (logistic regression) and univariate (Kolmogorov-Smirnov test) statistical procedures identified the duration of morning leaf wetness as a significant predictor of major infection events. Mean leaf wetness duration on days with minor and major infection events was 1.25 and 3.5 hours, respectively. The odds-ratio of the most significant logistic model was 2.2 (95 % CI 1.43 to 4.08; P = 0.0023), indicating that for every 1 hour increase in morning leaf wetness duration the odds of a major infection event were 2.2 times greater than the odds of minor infection event. Similarly, major and minor infection events were differentiated by the duration of morning leaf by
Kolmogorov-Smirnov tests (KS = 0.2748, P < 0.0001). Linear and non-linear regression indicated the concentration of airborne spores were positively correlated (R2 = 0.73) with disease incidence, indicating that modeling sporulation may provide a reliable means for predicting disease.
Impacts
Hop downy mildew is one of the most economically important diseases of hops grow in the US, and management relies largely on prophylactic fungicide applications. Disease forecast models can aid growers in improved use of pesticides. Research thus far has shown that three sprays can be eliminated by use of the growing-degree day and infection risk model, without reducing control of the disease. If 50 % of the U.S. hop acreage is managed with the aid of this disease forecasting system, 15,000 pounds of fungicide would not be applied annually and would save producers an estimated $900,000 annually in pesticide and application costs; helping grower profitability as well as reducing pesticide use and associated environmental impacts.
Publications
- No publications reported this period
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