Eastern filbert blight (EFB) and pacific flatheaded borer (PFB) are two problems of Pacific Northwest orchard and nursery production. Fungicides and insecticides used to manage these issues are typically applied to plant tissues with minimal foliage present that can result in considerable spray waste or drift. The Intelligent Spray System (ISS) is a laser-guided, variable-rate sprayer that detects objects in the target zone and releases spray volumes proportional to the density of plant tissues, thereby increasing application efficiency and reducing waste. However, the ISS has not been tested when targeting low-foliage plant tissues such as emerging shoots and trunks. Three experiments were conducted from 2018 to 2021 to evaluate the potential use of the ISS for EFB and PFB management by assessing spray coverage on emerging hazelnut shoot tips, hazelnut tree trunks, and maple tree trunks. On hazelnut shoot tips, coverage was <10% of the shoot on both adaxial and abaxial sides, with the highest coverage on the adaxial side (9.5%) resulting from spraying in standard mode (no sensors) at 3.1 kph. On hazelnut trunks, application at the slowest tested speed (3.1 kph) in intelligent mode resulted in spray coverage greater than or equal to that applied in standard mode at 5.1 kph. In addition, coverage was significantly higher on cards placed on the ground between trees when the sprayer was used in standard mode, indicating higher amounts of wasted spray and drift over intelligent mode. On maple trunks, the slowest speed tested (3.1 kph) resulted in the highest coverage of tree trunks facing the sprayer that were two and three rows away from the sprayer, with the highest coverage levels on the row of trees closest to the sprayer occurring at the highest tested speed of 6.4 kph. On cards placed on trunk sides not facing the sprayer, the slowest tested speed of 3.2 kph resulted in significantly higher coverage than both treatments at 6.4 kph and intelligent mode at 4.8 kph in the tree row closest to the sprayer. This work has demonstrated a baseline of coverage that hazelnut buds receive when spraying for EFB, illustrates that the ISS was able to effectively target trunks, and could be an alternative to drenches for PFB control.

Organic blueberry production in the PNW has many challenges, including diseases like mummy berry caused by the fungus Monilinia vaccinii-corymbosi (Reade) Honey. Management recommendations focus on reducing overwintering pseudosclerotia, however, it is unknown how long they survive. Based on qualitative observations pseudosclerotia are hypothesized to survive multiple years after contact with the soil surface. The development of apothecia from M. vaccinii-corymbosi pseudosclerotia was evaluated over multiple years at a location without a history of blueberry production. A total of 1,000 pseudosclerotia were placed on field soil plots in 2018 and replicated eight times. Another 100 pseudosclerotia were placed in wire corrals on field soil and replicated fifteen times. Plots and corrals were regularly examined each spring for the emergence of apothecia. The pseudosclerotia were able to survive, germinate, and produce apothecia for up to five years after their placement. Very few pseudosclerotia produced apothecia in any year, varying from 0 to 18 at any observed time. Pieces of partial or whole pseudosclerotia were observed for up to three years after placement. Our study shows that a pseudosclerotial “seed bank” exists under blueberry bushes, necessitating a long-term implementation of mummy berry cultural management tactics.

To optimize pesticide applications to the canopies of deciduous perennial crops, spray volume should be adjusted throughout the year to match the changes in canopy volume and density. Machine-vision, computer-controlled, variable-rate sprayers are now commercially available and claim to provide adequate coverage with decreased spray volumes compared with constant-rate sprayers. However, there is little research comparing variable- and constant-rate spray applications as crop characteristics change throughout a growing season. This study evaluated spray volume, spray quality (e.g., coverage and deposit density), and off-target spray losses of variable- and constant-rate sprayers across multiple phenophases in an apple ( Malus domestica ) orchard and a grape ( Vitis vinifera ) vineyard. The variable-rate sprayer mode applied 67% to 74% less volume in the orchard and 61% to 80% less volume in the vineyard. Spray coverage (percent), measured by water-sensitive cards (WSC), was consistently greater in the constant-rate mode compared with the variable-rate mode, but in many cases, excessive coverage (i.e., over-spray) was recorded. The variable-rate sprayer reduced off-target losses, measured by WSC coverage, up to 40% in the orchard and up to 33% in the vineyard. Spray application deposit densities (droplets per square centimeter) on target canopies were typically greater in variable-rate mode. However, the deposit densities were confounded in over-spray conditions because droplets coalesced on the WSC resulting in artificially low values (i.e., few, very large droplets). Spray efficiencies were most improved early in the growing season, when canopy density was lowest, demonstrating the importance of tailoring spray volume to plant canopy characteristics.

Grapevine powdery mildew (GPM), caused by the fungus Erysiphe necator, is a constant threat to worldwide production of grape berries, requiring repeated use of fungicides for management. The frequent fungicide applications have resulted in resistance to commonly used quinone outside inhibitor (QoI) fungicides and the resistance is associated with single-nucleotide polymorphisms (SNPs) in the mitochondrial cytochrome b gene (cytb). In this study, we attempted to detect the most common SNP causing a glycine to alanine substitution at amino acid position 143 (i.e., G143A) in the cytb protein, to track this resistance using allele-specific TaqMan probe and digital-droplet PCR-based assays. Specificity and sensitivity of these assays showed that these two assays could discriminate SNPs and were effective on mixed samples. These diagnostic assays were implemented to survey E. necator samples collected from leaf and air samples from California and Oregon grape-growing regions. Sequencing of PCR amplicons and phenotyping of isolates also revealed that these assays accurately detected each allele (100% agreement), and there was an absolute agreement between the presence or absence of the G143A mutation and resistance to QoIs in the E. necator sampled. These results indicate that the developed diagnostic tools will help growers make informed decisions about fungicide selections and applications which, in turn, will facilitate GPM disease management and improve grape production systems.

Many specialty crops are susceptible to insects and diseases, and as such are reliant on regular canopy pesticide applications to achieve quality attributes required for salability. The majority of specialty crop producers continue to use antiquated pesticide application technologies for directed canopy spraying such as the radial air blast sprayer that has been associated with chemical wastage and off-target drift of around 40% and 15% of total applied spray volume, respectively. However, precision sprayers are available that result in remarkable improvements to these parameters. The wide-scale adoption of precision sprayers by specialty crop producers remains low. Reasons for the continued dominance of old technologies include risk averseness of farmers and regulatory bottlenecks. However, as farm labor becomes more expensive, less available, and consumers and regulations favor sustainably produced products, motivations to improve spray application efficiency are increasing. While there are many opportunities and future directions application technology may take, sensor-controlled sprayer technology that applies a proportionate amount of spray will likely be the primary technology of precision sprayers going into the future. (c) 2020 Society of Chemical Industry

Grape powdery mildew (GPM) fungicide programs consist of 5 to 15 applications, depending on region or market, in an attempt to achieve the high fruit quality standards demanded by the market. Understanding how fungicides redistribute and targeting redistributing fungicide to critical crop phenological stages could improve fungicide protection of grape clusters. This study evaluated fungicide redistribution in grapevines from major fungicide groups labeled for GPM control. Translaminar and xylem redistribution was examined by placing fungicide-impregnated filter disks on the adaxial or abaxial leaf surface of detached leaves for 10 min and then incubating for 48 h before inoculating the abaxial surface with conidia. Vapor redistribution used Teflon disks sprayed with fungicides and placed on the abaxial leaf surface of detached leaves 48 h before inoculation. Disease development was rated 10 days later. Translaminar movement through calyptra was tested using flowering potted vines. All fungicides tested redistributed through at least one mechanism. Fungicide timing at critical phenological stages (early, mid, and late bloom) was assessed in small plots of cultivar Pinot noir vines. The application of trifloxystrobin, quinoxyfen, or fluopyram at different bloom stages showed that applications initiated at end of bloom resulted in the lowest berry infection probabilities of 0.073, 0.097, and 0.020, respectively. The results of this study suggest that integrating two carefully timed applications of redistributing fungicides initiated at end of bloom into a fungicide program may be an effective strategy for wine grape growers in western Oregon to produce fruit with low GPM infection.

Wine grapes are an important agricultural commodity in the Pacific Northwest, where grape powdery mildew (GPM) is one of the main disease problems. The efficacy of various sulfur concentrations and output volumes from an air blast sprayer retrofitted with the Intelligent Spray System (ISS) were evaluated for the management of GPM. The ISS consists of a LiDAR sensor, Doppler speed sensor, embedded computer, flow controller, and individual pulse-width-modulation solenoid valves at each nozzle. GPM cluster severity ranged from 55 to 75% across all trials in the study when the ISS was used at its default spray rate of 62.5 ml/m3 with micronized sulfur at 6 g/liter, which was significantly higher than all other fungicide treatments but lower than nontreated controls. Similarly, leaf incidence values were highest on nontreated vines, followed by micronized sulfur at 6 g/liter applied at 62.5 ml/m3, with all other fungicide treatments being significantly lower in all trials. Using the ISS at the 62.5 ml/m3 rate and a rotation of locally systemic fungicides resulted in the lowest observed GPM leaf incidence and average cluster severity of 11% in both 2019 and 2020, the lowest cluster severity of all fungicide treatments tested. GPM control with the ISS and micronized sulfur was equivalent to a constant-rate air blast treatment at 6 g/liter when the spray rate of the ISS was increased to 125 ml/m3 or the concentration of sulfur was increased to 24 g/liter. In those cases, the amount of sulfur applied to vines was at or above the minimum label rate from bloom until the end of the season, or the entire season, respectively. This study has shown that sufficient disease control cannot always be expected when pesticides are mixed at the same rate as would be used for a constant-rate sprayer in a variable rate sprayer, especially when contact fungicides such as sulfur are used. With appropriate adjustments, the variable-rate ISS can be a useful tool to reduce pesticide quantities, water needed for mixing, and as a result labor, because fewer trips to refill for a given spray event are needed.

Oregon State University • University of Idaho • Washington State University PNW 727 • Published June 2019 Brent W. Warneke, faculty research assistant; Jay W. Pscheidt, Extension plant pathology specialist and professor; both of Department of Botany and Plant Pathology; Robin R. Rosetta, Extension horticulturist, nursery crop pest management; Lloyd L. Nackley, assistant professor; both of North Willamette Research and Extension Center; all of Oregon State University Due to intense pressure from pests and diseases, specialty tree crops such as fruits, nuts, and ornamentals currently rely on regular applications of pesticides to produce marketable varieties. Many of the pesticide application technologies used today are based on airassisted sprayers, also known as air-blast sprayers. These sprayers are versatile, reliable, and can be modified to fit many types of crops, all of which are reasons for their continued popularity.