Adjusting Product Timing during the Powdery Mildew Critical Window to Improve Disease Management

Transcription

1 ASEV CATALYST REPORT Adjusting Product Timing during the Powdery Mildew Critical Window to Improve Disease Management Michelle M. Moyer, 1 * Jensena M. Newhouse, 2 and Gary G. Grove 3 1 Associate Professor, Dept. of Horticulture; 2 Former research technician, Dept. of Horticulture; and 3 Professor, Dept. of Plant Pathology; Washington State University Irrigated Agriculture Research and Extension Center, N. Bunn Rd., Prosser, WA. *Corresponding author (michelle.moyer@wsu.edu) Acknowledgments: The authors would like to thank Mauricio Garcia, Brittany Komm, Katherine East, Steve Hoff, and Eric Gale for their technical assistance. This work was partially supported by the USDA National Institute of Food and Agriculture, Hatch Project #226789, and a grant from the Washington State Grape and Wine Research Program. Manuscript submitted Jan 2, 2018; revised May 2, 2018, May 8, 2018; accepted May 11, 2018 Copyright 2018 by the American Society for Enology and Viticulture. All rights reserved. Summary Goals: This project was designed to answer questions relating to the timing of different cultural (leaf removal) and chemical (fungicide rotation) disease management practices and how they influence the overall efficacy of a powdery mildew management program. Key Findings: The timing of specific chemical modes of action play an important role in overall powdery mildew fungicide program efficacy. In this study, programs with the evaluated products applied once during the critical window performed equally well to programs with the same evaluated products applied twice (critical window and bunch closure), emphasizing 1 Copyright 2018 by.

2 the idea that disease control on fruit is controlled by critical window sprays rather than laterseason sprays. As expected, leaf removal significantly improved spray coverage in the fruit zone; however, this improved coverage did not last the entire season. Canopy refill, due to the development of summer laterals, reduce fruit-zone coverage later in the season. Leaf removal also did not result in any positive additive effects for overall disease control. Impact and Significance: Overall, these findings can be used to aid growers in selection and rotation of products in their powdery mildew management programs to maximize both disease control efficacy and minimize fungicide resistance development risk. While early fruit zone leaf removal did not improve overall disease control in this high-pressure scenario, the resulting improved spray coverage in the fruit zone may enhance disease control when low-volume spray applications or contact-active chemistries are emphasized in a commercial program. 38 Key words: fungicide resistance, ontogenic resistance, spray programs Overview Management of grapevine powdery mildew was significantly altered with the discovery of ontogenic, or age-related resistance 1. This discovery demonstrated that grape berries were at their peak susceptibility to the grape powdery mildew pathogen during a limited window of development, from approximately prebloom to three to four weeks post-fruit set. This critical window concept for aligning spray programs to vine phenology has resulted in improved timing and reduction in overall number of pesticide applications; in Washington alone, educational efforts in the last five years that have focused on phenology-based mildew management has 2

3 reduced the average number of annual sprays by one to two applications and has saved the industry approximately $2,000,000 USD annually 2. However, even in a climate that is normally classified as an arid steppe 3 there can be years where mildew management is challenging. Such years were experienced in 2010 and 2011, which were characterized by cooler and wetter-than-average conditions 4. In these years, the standard six to eight sprays a season 5 was insufficient at managing mildew in many commercial settings. However, some growers were still able to achieve control with three sprays 6. In 2015 and 2016, years that were considered ideal for maximum mildew control (hot, dry, sunny), there were some growers who achieved acceptable control with only two sprays total 7. How is it that some programs, that are not limited to specific product selection, achieve equivalent control using only 25-50% of the industry standard number of sprays? There are clearly several factors that can influence disease control, not limited to proper sprayer calibration, ground speed at the time of application, and canopy management. However, one common factor for several of these low-frequency applicators was the choice of products used and the specifically-chosen timing of spray applications. The trial presented here aimed to evaluate and answer the question of Is timing really everything? particularly in context to key grapevine phenological stages for mildew management, and different chemical modes of action that are commonly used in conventional vineyard production systems. The concept of timing was approached using fungicide rotation programs that focused on the application of one of three different fungicide modes-of-action during different points between immediate prebloom and post-fruit set. Different fungicide modes-of-action are often annotated on their respective use labels as a specific FRAC group (multiple groups if the 3

4 product is a pre-mix of different fungicides). The term FRAC is an acronym for the Fungicide Resistance Action Committee 8, an international group composed of different industry specialists (private companies, university researchers) dedicated to developing information on how to effectively deploy fungicides to prolong their effective use and slow the process of fungicide resistance development. Fungicides that have similar properties are grouped into the same FRAC category. The active ingredients chosen were quinoxyfen (FRAC 13), cyflufenamid (FRAC U6) and metrafenone (FRAC U8), which were applied in a background spray program of myclobutanil (FRAC 3; Table 1). In Washington, there is a heavy reliance on FRAC 3 and strobilurin (FRAC 11) fungicides; there is also documented fungicide resistance to FRAC 11 9 fungicides and concerns that FRAC 3 fungicide resistance may be developing. Thus, while the use of these potentially compromised products can still be viable options within a spray program (provided they are tank mixed with another, non-compromised FRAC group), there is a growing demand to know how other FRAC group products perform, and perform optimally, during the critical window for mildew management Major Observations and Interpretations Disease ratings: In 2013, fungicide program 10 (Table 1) significantly influenced disease outcome (p < ; Fig 1A). All programs outperformed the untreated control. Program M2, which had a metrafenone application at full bloom, performed the best, whereas Q1 (quinoxyfen at prebloom), and C2 (cyflufenamid at bloom) were intermediate to M2 and the remaining programs. Leaf removal did not statistically influence cluster disease severity (p = 0.311). In 2013, disease was consistent throughout the vineyard block, likely due to consistent rains that 4

5 occurred at the end of June that increased canopy growth (i.e., new tissue for disease infection), and humidity in and surrounding the canopy (Fig. 2). In 2014 we saw similar results, where fungicide programs significantly influenced disease outcome (Fig. 1B), and leaf removal nested within fungicide programs did not (p = 0.07). As in 2013, all programs outperformed the untreated control. In 2014, program Q4, which consisted of a post-fruit set application of quinoxyfen and was the best-performing program was significantly better than program C3, which had a fruit set application of cyflufenamid. All remaining programs were intermediate in performance to these two. Of interest is the comparison of the Q2 treatment to other Q treatments. Program Q2 had both early (full bloom) and late-season (bunch closure) applications of quinoxyfen and was the only quinoxyfen program with this dual application. A typical assumption would be that the added end-of-program application would improve disease control, but in both 2013 and 2014, its performance was not significantly different than the other, single-timed applications of quinoxyfen that occurred either just before or during the critical window for fruit infection. This highlights how the duration of ontogenic susceptibility could influence the perception of product performance 1 fruit was already resistant at bunch closure, and thus, additional fungicides directed to control cluster disease severity at this time did not have any impact on season-long disease control; but if a field manager only had a program with this dual application, it might be assumed that the late-application is necessary to achieve that level of disease control on the fruit. However, the full-bloom application was likely carrying most of the control for that program. We see this repeated in 2014, when both the cyflufenamid and metrafenone had similar comparable treatments a program timing that had a dual application of an early (full bloom) 5

6 and late-season (bunch closure) treatment (C2, M2), and then a single application at fruit set (C3, M3). In both cases, the dual applications were not statistically better than the single applications (Fig. 1), reinforcing the idea that management of grape powdery mildew on clusters should be emphasized earlier in the growing season, rather than later. Of consideration for placing disease management into seasonal context is the consideration of vine development differences between the two years. As noted in Table 1, 2014 was a much faster vine development year than All phenological stages started on earlier calendar dates in 2014 when compared to Typically, in eastern Washington, earlier growing seasons are related to warmer winters. In most cases, when the region has warmer winters and earlier starts to the growing season, phenological stages can become protracted (extended) due to less-than-optimal winter chilling. As such, while a bloom spray is a single date at a specified time (Table 1), the duration of bloom following a warmer winter can be longer and in a longer period of practical vineyard susceptibility than the duration of bloom following a colder winter, holding in-season weather conditions constant. A major consideration for any trial that is rating the efficacy of a product or a program on disease management is that of the consistency of disease outbreaks that are typically seen on fruit. While coverage, as determined by spray penetration, was measured, there is always potentially associated error in product delivery related to machine operation. While the sprayer used in this study was calibrated at the start of the season, calibration was not re-assessed throughout the year to ensure that nozzle wear or misalignment had not occurred. This could be a reason for the variation seen in cluster disease severity, as evenness of product delivery would ultimately influence evenness of cluster disease severity. 6

7 Spray coverage. In 2013, spray coverage was only evaluated on one day (Fig. 3); coverage evaluation occurred four times in 2014 to more effectively see how leaf removal influenced spray penetration over time (Fig. 3). In 2013, coverage was assessed on 2 July, which was 46 days after prebloom leaf removal, 25 days after the bloom leaf removal, and three days prior to post-bloom leaf removal. As seen in Fig. 3, even at several weeks post-leaf removal, its effects on increasing spray penetration were still observed. In 2014, spray coverage assessment occurred four times; (i) 11 days after prebloom leaf removal (Fig. 4A), (ii) three days after bloom leaf removal (Fig. 4B), (iii) six days after post-bloom leaf removal (Fig. 4C), and (iv) a followup, near end of season assessment on 31 July (Fig. 4D). As noted, when leaf removal had occurred, spray coverage was significantly improved; however, by the end of the season, the prebloom leaf removal treatment was no longer effective at improving spray coverage in the fruit zone due to canopy refill from lateral shoot development. Fruit quality assessments. In both years, the timing of leaf removal did not influence fruit quality (Brix, titratable acidity, or juice ph); however, fungicide program did influence fruit quality (Table 2). Even then, there were not many differences between the untreated control and regular fungicide programs and final fruit quality as measured by Brix, titratable acidity, or juice ph. In 2013, Program Q3, which had an application of quinoxyfen at fruit set, had the highest Brix and the higher juice ph (in this case, higher ph was desirable due to overall low ph of the fruit). This program also performed well in 2014 and was not statistically different from the highest performing programs (based on juice Brix), which were programs Q2 and M2. These programs had either quinoxyfen (Q2) or metrafenone (M2) at full bloom. Both programs performed equally well in 2013 as well. Past reports have also indicated that powdery mildew 7

8 diseased fruit can result in off-flavors in the final fermented product 11 ; that aspect was not evaluated in this study, and the lack of disease control in some of the fungicide programs, while no major differences in initial fruit quality, could lead to differences in wine quality Broader Impact The understanding of grape powdery mildew management has progressed past when to spray and what to spray; we know the general efficacies of many standard products, and we know when key periods for infection and disease development are in vineyards. At the same time, however, we juggle maximizing disease management programs with managing fungicide resistance development and labor availability. Our field trial here is a part of the exploration on how to be the most efficient with different chemical modes of action within a season s spray program, while still incorporating cultural practices. The intention is to define windows in management where specific modes of action may have their top performance, thus providing guidelines to help with the planning of fungicide rotations. Just as with other studies which use ontogenic resistance as a basis for developing spray programs 12, we saw that the best program performance was achieved when management was focused early (fruit set and earlier) in the growing season, regardless of product mode of action. By improving the timing of specific chemical modes of action within a spray program and using different modes of action during the critical window for infection, disease can be effectively managed while being mindful of the risks of fungicide resistance development that can arise from repeated use of the same chemical mode of action. The authors would like to emphasize, however, that while product selection and timing are key components to disease 8

9 management, they are irrelevant if the product does not make it to the plant sprayer functionality and appropriate selection of water carrier volume to match canopy size are also critical components to a good management program. Under the disease pressure 13 that occurred in this trial, leaf removal should not be considered as a stand-alone management option. In some cases, it may enhance disease on clusters by exposing them to high levels of powdery mildew inoculum when they are not protected by a fungicide. In other words, if cultural practices such as fruit zone removal are a part of a management program, their timing should be considered as a part of the management regime. In the case of mildew management, leaf removal should not occur immediately after a fungicide spray, as it would be removing product from the vineyard. It should also not occur substantially before a fungicide spray, leaving clusters exposed for potential infection. Ideally, leaf removal would occur within a day or two preceding a fungicide application Experimental Design Vineyard description. Experiments were conducted at the Washington State University Irrigated Agriculture Research and Extension Center s Roza Research Farm (lat ' 24'' N; long ' 48'' W) during the 2013 and 2014 growing seasons. The approximately 1 ha vineyard was a mixed planting of own-rooted Vitis vinifera Chardonnay and Riesling planted in 2001; only Riesling was used for the experiment to eliminate potential cultivar influence. Vines are planted on a 1.8 m x 2.7 m (6 ft vine x 8 ft row) spacing, with north-south row orientation. Vines were spur pruned, trained to a modified vertical shoot position system with a single set of mobile catch wires above the cordon, drip-irrigated, with a weed-free strip 9

10 chemically maintained directly under vines, and natural vegetation maintained between the rows managed with periodic mowing. This block is reserved for pathology experiments, and as such, the eastern and western most rows have remained unsprayed since planting to provide a sufficient reservoir of E. necator inoculum. Weather data was collected using the Washington State University s AgWeatherNet system 14. The Roza weather station was used and is located within 4 m (13 ft) of the experimental vineyard. Daily maximum and minimum air temperatures, and daily total precipitation for 2013 and 2014 are presented in Figure 2. Fungicide treatments. Specific fungicide treatments and application timing are listed in Table 1. This rotation was chosen to see effects of specific fungicide timing in a complete program rotation on final cluster disease severity. Fungicide treatment replicate plots consisted of six vine panels; data was collected from the center four vines (Fig. 5). Individual fungicide treatments were replicated four times. Treatments were applied using a modified Rears sprayer with a custom-built boom equipped with seven flat spray brass nozzles (TeeJet 8006; TeeJet Nozzles) at 100 psi (nozzle output at 1 gal/min). The sprayer consisted of three tanks, two 95 L tanks and one 189 L tank. Tractor speed was 3.2 to 4.8 km/hr (2 to 3 mph). Total water volume applied changed with the developing canopy; the first spray was applied using three nozzles resulting in L/ha (45 gal/acre). The second spray was applied using five nozzles resulting in L/ha (75 gal/acre); the remaining sprays were applied using seven nozzles at L/ha (105 gal/acre). Regardless of total water volume applied, the product rate consisted of the following per-hectare equivalents: myclobutanil (Rally) at g (5 oz/acre); quinoxyfen (Quintec) at ml (4 fl.oz/acre); cyflufenamid (Torino) 10

11 at ml (3.4 fl. oz/acre); and metrafenone (Vivando) at ml (15.4 fl. oz/acre). All treatments were applied with a surfactant (Break-Thru) at 62.5 ml/l (8 fl. oz/gal). The control treatment was unsprayed and used to develop a baseline idea of disease pressure in the block. As a general good practice when evaluating fungicide performance, untreated controls are recommended to determine if control was due to the actual product, and not due to nonconducive environmental conditions or low inoculum levels. Leaf removal treatments. Fruit zone leaf removal consisted of removing leaves on a shoot from the base of the shoot up and adjacent to the secondary cluster. Leaves were removed on the east side of the canopy, as per common practice in eastern Washington. The different timing of fruit zone leaf removal treatments evaluated were: a control (no leaf removal), prebloom (when 50% of the clusters were at rachis elongation), bloom (when 50% of the clusters were at 50% capfall), and 4 weeks postbloom. In 2013, leaf removal treatments were implemented on 17 May (prebloom), 7 June (bloom), and 5 July (4 weeks postbloom). In 2014, leaf removal treatments were implemented on 30 May (prebloom), 16 June (bloom) and 11 July (4 weeks postbloom). Fruit zone leaf removal treatments were nested within each fungicide treatment. Of the four center data vines in each fungicide treatment replicate plot, one vine was dedicated to each leaf removal treatment. As with fungicide treatments, leaf removal within each fungicide treatment, was replicated four times. Spray coverage. Spray coverage was evaluated in the leaf removal treatments using water-sensitive cards (Syngenta Crop Protection AG, Basel, Switzerland). Cards were affixed to the node between the basal and secondary clusters using a clothespin, water-sensitive side facing east. The cards were placed in the vineyard just prior to spraying and were removed 11

12 promptly after they had dried in the field (approximately 2 to 3 hrs). Four cards placed in each leaf-removal subplot for one fungicide treatment in both 2013 and Coverage was visually estimated as percent area covered in three, 1 cm 2 areas per card. Spray coverage was assessed on 2 July in 2013, and was expanded to 10 June, 19 June, 17 July and 31 July in Disease ratings. Powdery mildew ratings were collected by visually estimating percent surface area of the cluster affected. Five clusters from each fungicide program plus leaf removal treatment replicate (a total of 20 clusters per fungicide treatment replicate) were nondestructively rated at the end of each growing season, on 18 Sept and 30 Sept Fruit quality assessments. To evaluate soluble solids (Brix), ph, and titratable acidity (TA) in the fruit, 3 whole clusters per fungicide + leaf removal treatment replicate were pressed in a 4 L plastic zip-top bag until all the berries were macerated. Juice from each bag was decanted into a dedicated 50 ml conical plastic centrifuge tube, and was used to determine soluble solids, ph and TA. Juice soluble solids were measured using a digital refractometer (Quick-Brix 60, Mettler-Toledo, Schwerzenbach, Switzerland). Juice ph was measured using a ph meter (InLab Versatile 413, Mettler-Toledo, Schwerzenbach, Switzerland). The same juice was then used for TA measurements 15. Statistical analyses. All statistical analyses were completed in JMP 9 (SAS Institute, Cary, NC), the linear mixed model platform, with fungicide treatment as a fixed effect, leaf removal treatment nested within fungicide treatment, and replicate as a random factor. Means separation was done using Tukey s HSD at α =

13 References and Footnotes 1. Gadoury DM, Seem RC, Ficke A and Wilcox W Ontogenic Resistance to Powdery Mildew in Grape Berries. Phytopathology 93: Hansen M. Research Leads to Better Control for Grape Disease. 25 May Good Fruit Grower. Washington State Fruit Commission, Yakima, WA. Online: Accessed 7 June The area receives approximately 200 mm of annual precipitation which predominately falls during the winter months. 4. Moyer MM and O Neal S Pest Management Strategic Plan for Washington State Wine Grape Production. Western Region IPM Center, USDA-NIFA. Online: 5. Moyer MM, Gadoury DM, Wilcox WF and Seem R Weather During Critical Epidemiological Periods and Subsequent Severity of Powdery Mildew on Grape Berries. Plant Dis 100: Grove G. Viticulturist (personal vineyard) Personal communication. 7. Hoff R, Director of Viticulture, Mercer Canyons Inc Personal communication; Schultz A, General Manager, Elephant Mountain Vineyards Personal communication. 8. Fungicide Resistance Action Committee: Specific information on FRAC fungicide categories are updated annually, and are found at: 9. Prengaman, K and Mullinax TJ. Resistance Rising for Powdery Mildew. 26 Feb Good Fruit Grower. Washington State Fruit Commission, Yakima, WA. Online: Accessed 2 May Fungicide program (Table 1) name abbreviations are designed to reflect the active ingredient (Q = quinoxyfen; C = cyflufenamid; M = Metrafenone), and the timing of that application relative to the timing of the spray during the Critical Window. For example, Q2 indicates that quinoxyfen was applied in the second spray during the period, whereas M3 indicates that metrafenone was applied in the third spray. 11. Gadoury DM, Seem RC, Wilcox WF, Henick-Kling T, Conterno L, Day A and Ficke A Effects of diffuse colonization of grape berries by Uncinula necator on bunch rots, 13

14 berry microflora, and juice and wine quality. Phytopathology 97: ; Ough CS and Berg HW Powdery mildew sensory effect on wine. Am J Enol Vitic 30:321; Stummer BE, Francis IL, Zanker T, Lattey KA and Scott ES Effects of powdery mildew on the sensory properties and composition of Chardonnay juice and wine when grape sugar ripeness is standardised. Aust J Grape Wine Res 11: Caffi T, Legler SE and Rossi V Evaluation of a warning system for early-season conrol of grapevine powdery mildew. Plant Dis 96: ; Gadoury DM, Seem RC, Ficke A and Wilcox WF Ontogenic resistance to powdery mildew in grape berries. Phytopathology 93: ; Gadoury DM, Pearson RC, Seem RC and Park EW Integrating the control programs for fungal diseases of grapevine in the northeastern United States. Vit Enol Sci 52: ; Moyer, MM, Gadoury DM, Wilcox WF and Seem RC Release of Erysiphe necator ascospores and impact of early-season disease pressure on Vitis vinifera fruit infection. Am J Enol Vitic 65: ; Moyer MM, Gadoury DM, Wilcox WF and Seem RC Weather During Critical Epidemiological Periods and Subsequent Severity of Powdery Mildew on Grape Berries. Plant Dis 100: Disease pressure is defined here as macro- and micro-climate conditions that are conducive for rapid disease development when the pathogen and host plant are present. For grape powdery mildew, the primary drivers for rapid disease development are moderate temperatures (Delp CJ Effect of temperature and humidity on the grape powdery mildew fungus. Phytopathology 44: ; Moyer MM, Gadoury DM, Cadle- Davidson L, Dry IB, Magarey PA, and Seem RC Effects of acute low temperature events on the development of Erysiphe necator and susceptibility of Vitis vinifera. Phytopathology 100: ; Choudhury RA, McRoberts N, Gubler WD Effects of punctuated heat stress on the grapevine powdery mildew pathogen, Erysiphe necator. Phyt Medi 53: ) and moderate to high relative humidity (Carroll JE and Wilcox WF Effects of humidity on the development of grapevine powdery mildew. Phytopathology 93: ). 14. AgWeatherNet can be accessed at: The samples were titrated to a ph of 8.20 using 0.1M sodium hydroxide (NaOH)

15 Table 1 Fungicide programs, their product rotation, and application dates for 2013 and Application Date May b (30cm shoot) 4 June (Prebloom) 18 June (Full bloom) 2 July (Fruit set) 16 July 30 July (Bunch closure) Program a Critical Window for Fruit Infection c Control Untreated Untreated Untreated Untreated Untreated Untreated Q1 myclobutanil quinoxyfen myclobutanil myclobutanil myclobutanil myclobutanil Q2 myclobutanil myclobutanil quinoxyfen myclobutanil myclobutanil quinoxyfen Q3 myclobutanil myclobutanil myclobutanil quinoxyfen myclobutanil myclobutanil Q4 myclobutanil myclobutanil myclobutanil myclobutanil quinoxyfen myclobutanil C2 myclobutanil myclobutanil cyflufenamid myclobutanil myclobutanil myclobutanil M2 myclobutanil myclobutanil metrafenone myclobutanil myclobutanil myclobutanil May b 22 July 28 May 10 June 24 June 8 July (Bunch (30cm shoot) (Prebloom) (Full bloom) (Fruit set) closure) Program a Critical Window for Fruit Infection c Control Untreated Untreated Untreated Untreated Untreated Untreated Q1 myclobutanil quinoxyfen myclobutanil myclobutanil myclobutanil myclobutanil Q2 myclobutanil myclobutanil quinoxyfen myclobutanil myclobutanil quinoxyfen Q3 myclobutanil myclobutanil myclobutanil quinoxyfen myclobutanil myclobutanil Q4 myclobutanil myclobutanil myclobutanil myclobutanil quinoxyfen myclobutanil C2 myclobutanil myclobutanil cyflufenamid myclobutanil myclobutanil cyflufenamid C3 myclobutanil myclobutanil myclobutanil cyflufenamid myclobutanil myclobutanil M2 myclobutanil myclobutanil metrafenone myclobutanil myclobutanil metrafenone M3 myclobutanil myclobutanil myclobutanil metrafenone myclobutanil myclobutanil a These programs were designed for experimental evaluation. The authors do not recommend, nor is it recommended on product labels, to repeatedly apply FRAC group 3 fungicides (demethylation inhibitors; DMI; e.g., myclobutanil) back to back in a fungicide program, or more than two times in a single growing season. Improper application of these and other fungicides can result in fungicide resistance development. Always rotate products, or tank mix high-risk products with contact fungicides when appropriate and compatible. b Budbreak: 27 Apr 2013 and 17 Apr c Defined from: Gadoury DM, Seem RC, Ficke A and Wilcox W Ontogenic Resistance to Powdery Mildew in Grape Berries. Phytopathology. 93:

16 Table 2 Fruit quality data for 2013 and Letters indicate means separation (within a year) using Tukey s HSD at α = Fungicide Program Brix Titratable Acidity (g/l) ph Control (ab) (cd) Q (ab) (d) Q (ab) (ab) Q (a) (a) Q (b) (ab) C (ab) (abc) M (ab) (bcd) 2014 Fungicide Program Brix Titratable Acidity (g/l) ph Control (ab) (a) 2.80 Q (ab) (ab) 2.78 Q (a) (ab) 2.80 Q (ab) (ab) 2.82 Q (ab) (b) 2.81 C (ab) (ab) 2.78 C (ab) (ab) 2.79 M (a) (ab) 2.78 M (b) (ab)

17 Figure 1 Cluster disease severity as a result of different fungicide programs in: (A) 2013 and (B) In both years, the timing of leaf removal did not influence powdery mildew disease severity on clusters overall, only fungicide treatment did. Letters denote significance between transformed fungicide treatment means using Tukey s HSD at α =

18 Figure 2 Daily maximum and minimum temperature, and daily precipitation for 1 April to 30 September in both 2013 (A) and 2014 (B). The 2013 growing season was marked by average temperatures and above average June precipitation, whereas 2014 was marked by above average temperatures, and below average spring precipitation. 18

19 Figure 3 Influence of leaf removal on mid-season spray coverage in the fruiting zone in Letters denote significance using Tukey s HSD at α =

20 Figure 4 Influence of leaf removal on early through mid-season spray coverage in the fruiting zone in Asterisks indicate treatments that had leaves removed prior to the spray date indicated. Letters denote significance using Tukey s HSD at α =

21 Figure 5 Field experimental design. Fungicide treatments were applied to a panel of six vines. To reduce potential carry-over from adjacent treatments, data was only recorded from the center four vines. Stakes in the ground marked start and stop points for fungicide application to aid the sprayer operator. Fungicide treatments were replicated four times. Leaf removal treatments occurred on a single vine within the panel and were replicated four times. 21