Gary G. Grove

A web-based decision support system to enhance IPM programs in Washington tree fruit.

BACKGROUND Integrated pest management (IPM) decision-making has become more information intensive in Washington State tree crops in response to changes in pesticide availability, the development of new control tactics (such as mating disruption) and the development of new information on pest and natural enemy biology. The time-sensitive nature of the information means that growers must have constant access to a single source of verified information to guide management decisions. RESULTS The authors developed a decision support system for Washington tree fruit growers that integrates environmental data [140 Washington State University (WSU) stations plus weather forecasts from NOAA], model predictions (ten insects, four diseases and a horticultural model), management recommendations triggered by model status and a pesticide database that provides information on non-target impacts on other pests and natural enemies. A user survey in 2008 found that the user base was providing recommendations for most of the orchards and acreage in the state, and that users estimated the value at

Dynamic thermal time model of cold hardiness for dormant grapevine buds

16 million per year. CONCLUSIONS The design of the system facilitates education on a range of time-sensitive topics and will make it possible easily to incorporate other models, new management recommendations or information from new sensors as they are developed.

Powdery Mildew Severity as a Function of Canopy Density: Associated Impacts on Sunlight Penetration and Spray Coverage

BACKGROUND AND AIMS Grapevine (Vitis spp.) cold hardiness varies dynamically throughout the dormant season, primarily in response to changes in temperature. The development and possible uses of a discrete-dynamic model of bud cold hardiness for three Vitis genotypes are described. METHODS Iterative methods were used to optimize and evaluate model parameters by minimizing the root mean square error between observed and predicted bud hardiness, using up to 22 years of low-temperature exotherm data. Three grape cultivars were studied: Cabernet Sauvignon, Chardonnay (both V. vinifera) and Concord (V. labruscana). The model uses time steps of 1 d along with the measured daily mean air temperature to calculate the change in bud hardiness, which is then added to the hardiness from the previous day. Cultivar-dependent thermal time thresholds determine whether buds acclimate (gain hardiness) or deacclimate (lose hardiness). KEY RESULTS The parameterized model predicted bud hardiness for Cabernet Sauvignon and Chardonnay with an r(2) = 0·89 and for Concord with an r(2) = 0·82. Thermal time thresholds and (de-)acclimation rates changed between the early and late dormant season and were cultivar dependent but independent of each other. The timing of these changes was also unique for each cultivar. Concord achieved the greatest mid-winter hardiness but had the highest deacclimation rate, which resulted in rapid loss of hardiness in spring. Cabernet Sauvignon was least hardy, yet maintained its hardiness latest as a result of late transition to eco-dormancy, a high threshold temperature required to induce deacclimation and a low deacclimation rate. CONCLUSIONS A robust model of grapevine bud cold hardiness was developed that will aid in the anticipation of and response to potential injury from fluctuations in winter temperature and from extreme cold events. The model parameters that produce the best fit also permit insight into dynamic differences in hardiness among genotypes.

Perennation of Uncinula necator in vineyards of Eastern Washington

Variable canopy densities and associated differences in sunlight distribution within the fruit zones on clusters were quantified and correlated with variable severities of powdery mildew within vineyards in the states of New York, Washington, and South Australia. Canopy density was measured with enhanced point quadrat analysis (EPQA), and the number of shading layers and the photon flux within the fruit zone of individual vines indicated that less disease developed on clusters with more exposure to sunlight. When clusters were categorized as heavily shaded (≤10% photosynthetic photon flux), moderately exposed, or well exposed (≥51% photosynthetic photon flux), vines with the least disease were also shown to have a significantly greater proportion of clusters in the well-exposed category relative to vines with the highest powdery mildew ratings. Consequently, these latter vines had significantly more heavily shaded clusters. The correlation remained strong and the relationship linear even with biweekly applications of either 2 kg/ha or 9 kg/ha of wettable sulfur during the growing season. Additionally, through the use of a fluorescent tracer and EPQA assessments, the deposit of spray materials on clusters was shown to be linearly related to their degree of exposure. Thus, canopy management practices designed to optimize sunlight exposure of grape clusters for fruit quality purposes should also significantly assist in the management of powdery mildew.

Detection of Erysiphe necator in Air Samples Using the Polymerase Chain Reaction and Species-Specific Primers

Studies on the mode of perennation of Uncinula necator in Eastern Washington were conducted over a 4-year period. Evidence of perennation of U. necator in infected dormant buds was not evident during vineyard surveys conducted over the period. Cleistothecia retrieved from bark fissures and senesced leaves contained viable ascospores at bud burst and later. The proportion of cleistothecia retrieved from bark that contained viable ascospores at bud burst ranged from 0.19 to 0.48, 0.09 to 0.72, 0.18 to 0.22, and 0.48 to 0.67 in 1998, 1999, 2000, and 2001, respectively. Viability of cleistothecia retrieved from senesced leaves in two vineyards at bud burst was 0.41 and 0.40 in 1998 and was 0.5 and 0.4 in 1999. Ascospore release in lab studies occurred from the late-dormant stage through the prebloom and (in some cases) the bloom stages. The initial ascosporic infection of Chardonnay leaves began at the late-dormant stage; colony numbers then declined through the prebloom and bloom stages. In vineyard studies, ascospores were trapped as late as 70 days after bud burst during rain events of 3.9 to 9.6 mm. Detection of ascospores in vineyard air preceded the initial occurrence of powdery mildew symptoms and signs and the occurrence of conidia in volumetric spore traps by several days. Cleistothecia are the only known source of primary inoculum in the grape-production regions of Eastern Washington.

Meteorological Factors Affecting Airborne Conidia Concentrations and the Latent Period of Podosphaera clandestina on Sweet Cherry

ABSTRACT A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or chasmothecia that were collected from grape leaves with a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique sequences of the internal transcribed spacer regions of E. necator. Using these primers in PCR amplifications, a 367-bp amplicon specific to E. necator was generated, but no amplicons were generated from other erysiphaceous species collected from 48 disparate hosts representing 26 vascular plant families. The PCR limit of detection was one to five conidia of E. necator placed directly into reaction mixtures or 100 to 250 conidia placed on glass rods coated with silicon grease. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. Amplification of E. necator DNA did not occur when the PCR assay was conducted on vineyard air samples collected while grapes were dormant or during periods when vine growth occurred but E. necator remained dormant. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the 3 years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this study represent the initial step toward the goal of incorporating an inoculum availability component into current and future grapevine powdery mildew risk assessment models.

Comparative Studies of Cryptosporiopsis Curvispora and C. Perennans. I. Morphology and Pathogenic Behavior

Conidia of Podosphaera clandestina were trapped beginning about 1 month after bud burst and continuing through the majority of the fruit development period and beyond. The presence of airborne conidia generally followed a diurnal pattern, with peak concentrations occurring in late morning to early afternoon. The three general spore dispersal patterns described by Sutton and Jones for P. leucotricha were observed: diurnal dispersal with concentrations peaking about midday (type I dispersal); random dispersal in which the spore concentrations were not correlated with any measured meteorological parameter (type II dispersal); and dispersal associated with the onset of rain (type III dispersal). Positive correlations with wind speed and temperature, and negative correlations with relative humidity, were characteristic of days when spore dispersal was diurnal. Consistent correlations with meteorological parameters were not detected on days with random or rain-onset dispersal. The latent period of P. clandestina on cherry foliage was found to be shortest at 20 to 25°C and was influenced by temperature and incubation time.

Persistence of Phenylamide Insensitivity in Pseudoperonospora humuli

Macroconidia of Cryptosporiopsis curvispora, cause of apple anthracnose, consistently displayed high curvature while those of C. perennans, cause of perennial canker, displayed low curvature when r...

Perennial canker of apple : seasonal host susceptibility, spore production, and perennation of Cryptosporiopsis perennans in infected fruit in eastern Washington

Downy mildew, caused by Pseudoperonospora humuli, is an important disease of hop in most production regions in the northern hemisphere. Insensitivity to phenylamide fungicides was detected in isolates of P. humuli in production regions in Oregon and Idaho in 1992, and these fungicides since have been used on a limited basis. In this study, the prevalence of phenylamide insensitivity among isolates of P. humuli collected from 2005 to 2007 in the northwestern United States was quantified using a leaf disk assay with a discriminating dose (25 μg/ml) of either metalaxyl or mefenoxam with inoculum derived from 201 systemically infected diseased shoots (basal spikes) collected from 6, 10, and 11 hop yards in Idaho, Washington, and Oregon, respectively. A subset of 47 basal spike isolates and 42 monosporic isolates collected from two yards in Idaho and nine yards in Oregon during 2006 and 2007 were assayed using a dilution series of metalaxyl to determine the effective dose that inhibited 50% of the incidence of sporulation (ED50). Insensitivity to mefenoxam was detected in 31 of 74 (41.9%) basal spikes collected from 13 hop yards. Insensitivity to the related compound metalaxyl was detected in 52 of 80 (65%) spikes collected from nine hop yards, including four hop yards in Washington. Log ED50 values ranged from -2.25 to 2.67 for basal spike isolates and -2.27 to 2.98 for monosporic isolates and had a similar distribution. Log ED50 values for monosporic isolates and entire basal spike isolates were significantly associated. However, the slope of the regression line was less than 1, indicating that the log ED50 values obtained from entire basal spike isolates were greater than the corresponding log ED50 values obtained from a monosporic isolate obtained from that spike. This research suggests that insensitivity to phenylamide fungicides is a stable phenotype in P. humuli. Management of downy mildew should rely on measures other than these fungicides in yards or regions where phenylamide insensitivity is prevalent, which is now known to include certain hop yards in Idaho, Oregon, and Washington.

Meta-Analysis Reveals a Critical Period for Management of Powdery Mildew on Hop Cones

Studies on the biology of Cryptosporiopsis perennans, causal agent of perennial canker and bulls-eye rot of apple, were conducted in orchards in eastern Washington during 1987-1990. Conidia were present on apple cankers throughout the year, with numbers peaking during November-February. The incubation and latent periods were 2-3 and 5-6 mo, respectively, on cankers resulting from artificial inoculation. In contrast to cankers resulting from natural inoculation, sporulation on these cankers was highest during the first year of canker growth and then declined. Trees were most susceptible to branch infection during the period from October to March (.)