A bright idea? Ultraviolet light as an integrative pest management tool for grape powdery mildew

Alexander Wong, Graduate Research Assistant, Dept. of Botany and Plant Pathology, OSU
Dr. Walt Mahaffee, Research Plant Pathologist, USDA-ARS and FRAME Networks group (USDA-NIFA-SCRI)

The concerning emergence of fungicide resistant grape powdery mildew (Erysiphe necator) to numerous fungicides (Beresford et al. 2016; Cherrad et al. 2018; Colcol et al. 2012; Colcol and Baudoin 2016; Kunova et al. 2016; Miles et al. 2012; Wong and Wilcox 2002) has led to a need for new integrative pest management strategies in grape production. Ultraviolet spectrum C (UVC) radiation has been used for over a century to kill or disable microorganisms by damaging their DNA. However, prolonged exposure times have been required because the microbes have very efficient DNA damage repair machinery (Beggs 2002). A recent discovery (Janisiewicz et al. 2016; Suthaparan et al. 2016) showed that this machinery is shut off at night to conserve energy, which indicates that UVC light applied at night might be effective with shorter exposure times (e.g., strawberry powdery mildew (Onofre et al. 2019), and wheat powdery mildew spores (Zhu et al. 2019)). In collaboration with David Gadoury at Cornell University and Michelle Moyer at Washington State University, we began testing whether UVC could be used to manage grape powdery mildew and bunch rot this past growing season.

Our research tests were conducted in a 22-year-old block of vertical shoot positioned (VSP) trellised Pinot noir trained at the OSU Botany and Plant Pathology Farm in Corvallis, Oregon using an over-canopy array of UVC light banks (Figure 1). UVC treatments were applied once per week, one hour after sundown at a speed of two or three miles per hour, which relates to a theoretical dose of 120 and 80 joules per square meter (J/m2), respectively. We also applied fungicide programs to subplots within rows of 5 lb/A sulfur on 7- to 14-day intervals, 10 fl oz/A Azoxystrobin on a 14-day interval, an alternation of sulfur and a QoI on a 14-day interval, or untreated control. Powdery mildew incidence ratings were performed every other week starting in mid-May and ending at veraison with leaf and cluster mildew severity ratings completed just before veraison. Grape powdery mildew leaf incidence was significantly (TukeyHSD, p < 0.05) reduced with weekly UV treatments (Figure 2). The UVC treatments did not lead to a significant reduction of mildew severity on clusters, mildew colonies, or rater’s gloves to monitor the amount of mildew (Thiessen et al. 2016) and presence of QoI resistance of each of the plots (Miles et al. 2020).

Botrytis cluster disease severity and incidence was measured at harvest after incubating clusters for 48 hours at 68°F and high humidity. There was no significant difference in Botrytis incidence between treatments. Due to the heavy mildew pressure, many of the clusters with high mildew severity had clusters too desiccated or decayed at harvest to be colonized by Botrytis. Botrytis isolates collected from diseased clusters are being tested for fungicide resistance.

These results suggest that UVC treatments, in conjunction with fungicide programs, has the potential to improve disease management of grape powdery mildew, but the frequency or dose of the application need to be increased. Future field studies at the BPP field site will examine increasing dose and/or UVC application frequency. In collaboration with Willamette Valley Vineyards and Saga Robotics, we will begin exploring the use of an autonomous drive base to apply the treatments on a commercial vineyard scale. Using UVC as part of an integrative pest management tool for powdery mildew will hopefully reduce costs and environmental impacts of disease management by reducing the amount of chemical inputs for disease control.

Figure 1. The tractor mounted UVC array in operation.

Figure 2. Area under disease progress curve for the powdery mildew epidemic based on foliar mildew incidence ratings. Error bars represent the standard error of the mean.

Literature Cited

Beggs CB 2002. A quantitative method for evaluating the photoreactivation of ultraviolet damaged microorganisms. Photochem Photobiol Sci 1:431-437.

Beresford RM, Wright PJ, Wood PN and Agnew RH. 2016. Sensitivity of grapevine powdery mildew (Erysiphe necator) to demethylation inhibitor and quinone outside inhibitor fungicides in New Zealand. N Z Plant Protec 69:1-10.

Cherrad S, Charnay A, Hernandez C, Steva H, Belbahri L and Vacher S. 2018. Emergence of boscalid-resistant strains of Erysiphe necator in French vineyards. Microbiol Res 216:79-84.

Colcol JF and Baudoin AB. 2016. Sensitivity of Erysiphe necator and Plasmopara viticola in Virginia to QoI Fungicides, Boscalid, Quinoxyfen, Thiophanate Methyl, and Mefenoxam. Plant Dis 100(2):337-344.

Colcol JF, Rallos LE and Baudoin AB. 2012. Sensitivity of Erysiphe necator to demethylation inhibitor fungicides in Virginia. Plant Dis 96(1):111-116.

Janisiewicz, WJ, Fumiomi T, Glenn DM, Camp MJ and Jurick WM. 2016. Dark period following UV-C treatment enhances killing of Botrytis cinerea conidia and controls gray mold of strawberries. Phytopathology 106(4):386-394.

Kunova A, Pizzatti C, Bonaldi M and Cortesi P. 2016. Metrafenone resistance in a population of Erysiphe necator in northern Italy. Pest Manag Sci 72(2):398-404.

Miles LA, Miles TD, Kirk WW and Schilder AMC. 2012. Strobilurin (QoI) resistance in populations of Erysiphe necator on grapes in Michigan. Plant Dis 96(11):1621-1628.

Miles TD, Neill T, Colle M, Warneke B, Robinson G, Stergiopoulos I and Mahaffee WF. 2020. Allele-specific detection methods for Qol fungicide resistant Erysiphe necator in vineyards. Plant Dis.

Onofre RB, Ortiz GA, de Mello Neto PP, Gadoury DM, Stensvand A, Rea M, Bierman A and Peres N. 2019. Evaluation of UVC for suppression of powdery mildew and other diseases of strawberry in open field production. In Technical Abstracts for the American Phytopathological Society (APS) Annual Meeting, Plant Health 2019. Cleveland, OH.

Suthaparan A, Solhaug KA, Stensvand A and Gislerød HR. 2016. Determination of UV action spectra affecting the infection process of Oidium neolycopersici, the cause of tomato powdery mildew. J Photoch Photobio B 156:41-49.

Thiessen LD, Keune JA, Neill TM, Turechek WW, Grove GG and Mahaffee WF. 2016. Development of a grower-conducted inoculum detection assay for management of grape powdery mildew. Plant Pathol 65:238-249.

Wong FP and Wilcox WF. 2002. Sensitivity to azoxystrobin among isolates of Uncinula necator: baseline distribution and relationship to myclobutanil sensitivity. Plant Dis 86(4):394-404.

Zhu M, Riederer M and Hildebrandt U. 2019. UV-C irradiation compromises conidial germination, formation of appressoria, and induces transcription of three putative photolyase genes in the barley powdery mildew fungus, Blumeria graminis f. sp. hordei. Fungal Biol 123(3):218-230.

Can Altering Canopy Shape Increase Productivity of Pinot noir: a new experiment at OSU’s Research Vineyard

Dr. R. Paul Schreiner, Research Plant Physiologist, USDA-ARS, Corvallis, OR

The newest block at Woodhall Research Vineyard is now six years old, and we will begin work in earnest next growing season to ask some fundamental production questions for Pinot noir. The key question is whether opening the top of a standard VSP training system (resulting in a Y-shaped canopy) will increase Pinot noir productivity without sacrificing quality (Figure 1). A second question is whether planting vines at a higher density impacts vine productivity or fruit quality. These questions are being addressed using a factorial experiment where two trellis treatments (traditional VSP & wide VSP) and two vine density treatments (3-foot and 6-foot in-row spacing) are applied in a randomized block design with five blocks. Each experimental plot has five continuous rows of vines about 100 feet long. Data will be collected from the middle three rows, allowing a border row of identical treatment on each side. Different crop levels will be applied to each of the trellis × density treatments by randomly assigning the north or south half of each plot to either low or high crop levels. The trellis and vine density treatments have been in place since 2015, and crop load will be manipulated for the first time next year. The vines were established using industry-standard practices (irrigation, fertilization, no crop in first two years, slowly increasing crop levels thereafter). In the last two years, vines were irrigated only twice each summer, when leaf water potential values reached about -1.4 MPa.

Why this design? Pinot noir producers in western Oregon use a VSP trellis system nearly exclusively where the shoots exist in a tight vertical plane that exposes only a small fraction of leaves to sunlight at midday when solar radiation is maximal. Opening the top of the trellis using a wide VSP system should increase net vine photosynthesis and the vine’s overall carbon budget, allowing more fruit to be produced per acre compared to a traditional VSP. This change can be implemented without removing the existing trellis, keeping costs low for this modification. A similar trellis design was shown to increase yield without compromising quality in Riesling vineyards (Reynolds et al. 1996). Pinot noir producers still thin crop to low levels, leaving 25-40% of their fruit on the vineyard floor. If opening up the canopy can allow Pinot noir producers to ripen more fruit per acre without negatively affecting quality, this approach can increase profits and sustainable production. Vine density per acre may also impact vine productivity or quality directly or by interacting with the altered trellis system. Still, such impacts cannot be predicted based on current knowledge. Since grafted grapevines cost about $5 each, reducing the number of plants needed per acre will significantly reduce establishment costs.

We have collected baseline data from the past five years. The block produced 2.2 US tons per acre in 2019 when the fruit was thinned to one cluster per shoot. Yield in 2020 was 2.5 tons per acre when no fruit thinning was applied due to low set in 2020. Thus far, yield has not been altered by the trellis or vine density treatments. However, vine vegetative growth based on pruning weights was altered for the first time in 2019. The high-density vines produced more shoot biomass in the wide VSP than the traditional VSP, but the low-density vines did not. Thus, the wide VSP appeared to capture more carbon than the traditional VSP in 2019, but only in high-density vines. We do not yet know if a similar response occurred in 2020 since pruning weights have not been obtained yet. Treatments have not altered yield parameters such as cluster weight and berry weight. Fruit composition based on must soluble solids, pH, titratable acids, and mineral nutrient concentrations has not been altered either. The application of different crop levels next year will result in a different yield, and this will begin to provide the true test of this experiment. I am excited to test these ideas on a large scale.

This research addresses improving vineyard production efficiency by altering the most common Pinot noir training system. If our hypothesis is correct, this research will improve Pinot noir wine grape growers’ profitability by increasing yield per acre, thus improving overall land and resource use efficiency.

Figure 1. Pinot noir in the Trellis Experiment at Woodhall Research Vineyard near midday on August 26, 2020. Top panel: Standard VSP. Bottom panel: Wide VSP. Note: larger shadow under Wide VSP vines.

Literature Cited

Reynolds AG, Wardle DA and Naylor AP. 1996. Impact of training system, vine spacing, and basal leaf removal on Riesling. Vine performance, berry composition, canopy microclimate, and vineyard labor requirements. Am J Enol Vitic 47:63-76.

Avoid mixing biologicals with antimicrobials

Dr. Jay W. Pscheidt and Lisa Jones, Dept. of Botany and Plant Pathology, Oregon State University

Actinovate AG (Streptomyces lydicus WYEC 108) and many other biological products are used in the management of organic grapes. Tank mixing more than one product is both economical and time-saving but tank mix compatibilities with biological control products such as Actinovate have not been thoroughly evaluated. In 2016, we examined the tank mix compatibility of Actinovate AG with commonly used organic products.

Actinovate AG was prepared at a concentration of 0.1g/ml. A 300 ml solution of Actinovate was prepared in a 500 ml beaker then mixed with each material and allowed to stand for 30 minutes. The mixture was then plated onto agar and incubated for 7 days at room temperature. The number of colony-forming units (CFU) of S. lydicus exposed in each mix was assessed daily and compared to an Actinovate plus water only control. The percentage of S. lydicus CFU in each tank mix compared to the CFU in the Actinovate control was calculated.

An average of 3.2×105 S. lydicus CFU developed after 7 days incubation on the various media when Actinovate was just mixed with water. Several products inhibited the growth of S. lydicus when prepared in as a mixture in the laboratory. No growth of S. lydicus was observed on plates when Actinovate was mixed with Horticultural Vinegar, a high rate of Regalia, Rex Lime Sulfur, Serenade Optimum, or Solubor DF. Less than 10% of the S. lydicus CFU grew when Actinovate was mixed with Biomin Calcium, Botector, Neptune’s Harvest 2-4-1 fish fertilizer, or Thuricide. Significantly fewer S. lydicus CFU grew when Double Nickel, the low rate of Regalia, Serenade Max, the high rate of Stimplex or Toggle were mix with Actinovate. There was no significant difference in the number of S. lydicus CFU that grew when Zen-O-Spore was mixed with Actinovate. The number of S. lydicus CFU was greater than double (219%) or quadruple (482%) that of the Actinovate control when mixed with Nitrozyme or the low rate of Stimplex, respectively.

Many of the biological products in this study grew quicker than S. lydicus under laboratory conditions. These fungi or bacteria generally outcompeted S. lydicus for space and resources on the agar plates. The fungus found in Zen-O-Spore was slower to grow and did not outcompete S. lydicus during the 7-day incubation.

This data does not imply a lack of or enhanced disease control in the field. For example, blueberry field trials over a 2-year period where Actinovate was mixed with Simplex did not result in disease control that was different than when either product was used alone. The data does indicate incompatibility between various products used in organic production.

For a complete data set please visit: http://sites.science.oregonstate.edu/bpp/Plant_Clinic/Fungicidebooklet/2016/Blueberry3.pdf