Organizations: Washington State University and Oregon State University

Cooperators: Mike Bush and Tim Smith

Contract Administrator: Sharon Taff ( 509-786-2226)




I.  Develop a risk index modes (utilizing rainfall, irrigation, temperature, relative humidity, and pathogen presence/activity) for initiating fungicide spray programs and adjusting subsequent spray intervals.  Research in 2005 will focus on disease development over a more broad range of relative humidities at 15-25 C.

II. & Develop means of detecting, identifying, and quantifying airborne propagules of P. clandestine early in epidemic progress.  Proof of concept was demonstrated in 2004.  In 2005 this information will be used to guide the initiation of the fungicide spray program.

III. & Develop and refine economically viable conventional and organic powdery mildew management programs.

IV.  Develop baseline sensitivities for resistance-prone compounds.  Preliminary studies focused on the DMI fungicides.  Future studies will concentrate on Qol and quinoline fungicides.

V. & Determine the effects of temperature and wetness on acute petroleum oil phytotoxicity.  Determine the chronic effects of oils on tree health.


Significant Findings:


  • Investigations on the temperature range where the cherry mildew fungus is active on cherry foliage were continued in 2004.  Disease develops between 10 and 27.5 C. Disease did not develop at 7.5 and 30C.
  • Cleistothecia (the primary inoculum supply) viability declined from 50% at bud burst to 0% at pit hardening.  The degradation of the ascospore supply required about 150 cumulative degree days> 10 C (50F).
  • The PCR primers developed by the R.A. Spotts research group were found to be highly specific for the cherry powdery mildew fungus.  The primers did not react with DNA collected from powdery mildews collected from 46 disparate hosts from 26 vascular plant families.
  • The PCR assay was found to be extremely sensitive:  It detected DNA extracted from 1-5


Cherry (SWEET) (Prunus avium "Bing")   J.D. Lunden and G.G. Grove

Powdery Mildew, Pdosphaera clandestine   Washington State University

Irrigated Agriculture & Extension Center  
24106 N. Bunn RD
Prosser, WA 99350-9642


Cherry Mildew control: sprayer type and volume comparisons, 2004

            Un-conventional air blast type orchard sprayers which rely on high air volume to shear water droplets to a small size are being used in the Pacific Northwest tree fruit industry.  This test was conducted to determine how this technology compares to traditional air-blast technology and whether satisfactory mildew control can be achieved using lower water volume with "wind shear" technology.  Treatments were made to 41-year-old Bing and Rainier cherry trees with an Accutech Sprayer (Columbia Blueline Manufacturing, Moxee WA) apply 25, 50, or 100 gallons per acre or a Pak-blast (Rears Manufacturing, Eugene, OR) applying 200 to 350 gallons per acre.  The 25, 50, and 100 gpa treatments applied from shuck fall to pit hardening wer done on a 7 day interval.  All other treatments were made on a 14 day interval.  Fungicide rates (active ingredient per acre) were uniform across all spray volumes.  Treatment rates, volumes and timings are presented in table.  Foliar mildew severity was determined between 29 June and 7 July by arbitrarily selecting twenty terminal shoots on each tree (five in each of the lower inner canopy, upper inner canopy, lower outer canopy, upper outer canopy).  Percent leaf area colonized by mildew was estimated visually on each of ten leaves beginning at the first fully expanded leaf beneath the shoot apex.  Mildew severity data from the three "Accutech" treatments was regressed against spray volume.


            Mildew control differences were evident amount treatments, although statistically significant mean separations existed only in inner lower canopy results.  In general, mildew control was directly related to spray volume among treatments applied with the Accutech Sprayer (r2 = 0.96).  Reducing the early spray interval (increasing the number of applications) for the lower volume treatments did not appear to replace the need for adequate spray volume.  Diminished control in the inner canopy was evident despite higher spray volumes with conventional spray technology.  Best outer canopy mildew control was obtained with conventional spray technology while "wind shear" technology seemed to proved improved control inside the canopy.  For both applicators mildew control diminished in the following order: Outer lower canopy, outer upper canopy, inner lower canopy, inner upper canopy.


Powdery Mildew Severity 


Treatment and Rate/AZ Volumn
Sprayer Canopy Canopy Canopy Canopy
Untreated 64.0a 89.85a 6.0a 22.1a
Styllet Oil 97% 1% 2.5 1,2,3,4
   Flint 50WG 3oz 2.5 5,7
   Procure 50WS 12oz 2.5 6 Accutech 19.1ab 36.3a 13.6a 51.3a
Styllet Oil 97% 1% 50 1,2,3,4
   Flint 50WG 3oz 50 5,7
   Procure 50WS 12oz 50 6 Accutech 6.45b 32.8a 1.1a 24.6a
Styllet Oil 97% 1% 100 1,2,3,4
   Flint 50WG 3oz 100 5,7
   Procure 50WS 12oz 100 6 Accutech .000b 21.05a .05a 9.8a
Styllet Oil 97% 1% 200 1,3
   Flint 50WG 3oz 200,300 5,8
   Procure 50WS 12oz 200,300 6 Rears Pak-Blast 32.5ab 43.3a 0.0a 9.1a


*Fomulated rater per acre or percent spray mix

*Dates for spray applications: 1 = 22 Apr; 2 = 30 Apr; 3 = 6 May; 4 = 13 May; 5 = 20 May, 6 = 2 June; 7 = 16 June; 8 = 25 June

*Percent of leaf area infected

*Means within a column followed by the same letter are not significantly different according to Tukey-Kramer HSD (PSO0.05)


Accutech (100 Gal/acre)
Accutech (50 Gal/acre)
Accutech (25Gal/acre)
  0  10  20 30  40 50 60 70


                                                   DISEASE SEVERITY

Figure 6. Effect of spray volume on cherry powdery mildew disease severity, 2004.  Fungisides were applied in spray volumes of 25, 50, and 100 gallons per acre using an Accutech sprayer.  Included for the purpose of comparison are results obtained using a conventional air-blast sprayer and untreated control.

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