Hop Cone Browning Managing Late Season Powdery Mildew


Hop Cone Browning: Managing Late Season Powdery ... - USA Hops

Hop Cone Browning: ManagingLate Season Powdery MildewDavid H. GentForage and Cereal Seed UnitUSDA-ARSARSCorvallis, Oregon

Hop Powdery Mildew

Hop Powdery Mildew

1009080702007 WeatherRain Temp RH Solar0. (in) 189 196 203 210 217 224 231 238 245 252 259Prosser 1 July – 15 Sept.0

2007 Powdery Mildew Risk Index10080Risk Index604020090 120 150 180 210 240Day of year

Cone Browning Associated withDiffuse Powdery MildewCourtesy WFM

Courtesy WFM

Powdery Mildew Risk Index1. If greater than 6 continuous hours above 86°F,subtract 20 points, else;2. If greater 0.1” rain, subtract 10 points,else;3. If greater than 6 continuous hours above 86°Con previous day, then no change in the index,else;4. If at least six continuous hours between 60-81°F, then add 20 points, else;5. If none of the above rules apply, then subtract10 points.

Powdery Mildew Colonies are Tolerant1to Leaf WetnessDisease severity0. duration (hr)8126241261224Hours afterinfection

1009080702007 WeatherRain Temp RH Solar0. (in) 189 196 203 210 217 224 231 238 245 252 259Prosser 1 July – 15 Sept.0

Alternaria Cone DisorderAlternaria alternata– Ubiquitous organism– Common in air of hop yards, leaves, and rootsof healthy plants– Decay organism: growth on senescent or deadplant tissue, leather, textiles, storage rots– Plant, animal, and human pathogen andallergen

Alternaria alternataFrom Rotem (1998):“In most cases A. alternata appears as a weakand opportunistic pathogen attackingsenescent or heavily stressed host plants, butin some cases it can be pathogenic to healthyand vigorously growing plants”• Infection primarly via wounds, senescenttissue, and/or flowers

S. J. PethybridgeAlternaria Cone Disorder• Associated withwind damage,high humidity,wet nights/drydays• Necrotic lesionson tips of bractsand bracteoles• 1 to 25% ofcone area

Alternaria Cone Disorder• Associated withprematuresenescence inUK on latematuring (mid-Sept.) varieties• Not known tocause yieldreductions inUK or AustraliaS. J. Pethybridge

Cone TissuesBractBracteole (w/ seed)Courtesy WFM

Alternaria Cone Disorder2007 IsolationsPM resistant:45% of conesCTZ:36% of conesOR PM resistant:71% conesConfirmed as A. alternata type by ITS sequence and conidial morphology

Alternaria Cone Disorder• 92% of isolations from bracts with lightto dark reddish-brown discoloration• Discoloration began from tips of bracts• Mostly on exposed portion of bracts• Cladosporium visible as dark sporulationon some bracts and bracteoles

Powdery Mildew (and Alternaria)Cone browning in2007 appeared to beassociated, primarily,with powderymildewInteractions withpowdery mildew?– Possible, but noobjective evidence tomy knowledge

Other Cone DiseasesFusarium cone tip blightSJPDowny MildewB. Englehard

Managing Late Season PowderyMildew• Always some risk on late maturing, powderymildew susceptible varieties• Management of powdery mildew on conesbegins in APRIL– Complete removal of all green tissue during springpruning– Application of fungicides before disease symptomsdevelop– Mid- to late season sucker control– Late season fungicide applications– Harvest timing

Association of PM on Leaves and Cones10080R 2 = 0.554Cone incidence60402000 20 40 60 80 100Leaf incidenceData from WA 2000 to 2006 CTZ

Flag Shoot Removal Delays Epidemics

Importance of Thorough PruningPruning Quality% FlagshootsExcellentModeratePoorAll02.1%12.4%21.2%9.3%0-0.50.511.9%19.2%74.1%13.8%>0.5%4.9%5.5%25.1%10.4%All4.4%11.9%21.2%10.4%n = 50 yards evaluated in 2000, 2005, and 2006; 12 OR and 38 WA

Grower Practices in Each Category1 = Excellent2 = Moderate3 = PoorCrowning (8)Scratch/Gramoxone(8)2X Gramoxone (3)2X Aim (2)1X Gramoxone (2)Gramoxone/Aim (1)Flamed/mowed x 2 (1)Scratch (6)Scratch/Gramoxone(3)Gramoxone/Aim (2)Flame (1)1X Aim (4)Flame (3)1X Gramoxone (1)Gramoxone/Aim (1)None (1)Other (2)22/25 (88%)3/13 (23%)0/12 (0%)

Summary• Pruning quality associated with amount ofdisease at harvest: 1X, 2X, 4X disease incones• Generally, excellent pruning associated with2 passes over field or aggressive crowning

Washington 2002: First Application201816and Cone IncidenceR 2 = 0.5908Cone Incidence (% )141210864204/14 4/19 4/24 4/29 5/4 5/9 5/14 5/19 5/24 5/29 6/3First Spray Date

Washington 2002: Last ApplicationCon e Inc i den ce (% )20181614121086420R 2 = 0.1952and Cone Incidence7/18 7/23 7/28 8/2 8/7 8/12 8/17 8/22 8/27 9/1 9/6Last Spray Date

Reduction in Cone Infection bySucker ControlData courtesy M. NelsonTreatment aAimCone infection (%)64.9 aDes-I-cate +GramoxoneNon-treated75.4 ab86.0 bAim: 6 July, 3 Aug, and 20 Aug in 60 GPA water; Gramoxone: 6 July, 3 Aug

August & September Fungicides• Part of an overall management system toreduce rate of epidemic development– Quintec and Pristine consistently among mostefficacious products registered• Quintec timing: Burr vs. Cones?– Target applications to protect developing conesduring disease favorable weather in August?

2007 Powdery Mildew Risk Index10080Risk Index604020090 120 150 180 210 240Day of year

Percent1009080706050403020100Effect of fungicide timing on hoppowdery mildew cv. Zeus – 2007LeafinfectionJuly 11LeafinfectionharvestConeinfectionharvestQ,F 2wk post burnback*F,Q 2wk post burnback*Q,F 1000 GGD postburnback**F,Q 1000 GGD postburnback**Q,F Model***F,Q Model***Non-treatedQ= Quintec, F = Flint* 7 applications, ** 4 applications, *** 9 applications.

% Cone infection% Cone infectionEffect of disease pressure on fungicide efficacy1009080706050403020100Moderate pressureHigh pressureQuintec 6 fl ozQuintec 4, 6 & 8fl ozFlint alt. AccrueFlint alt. FolicurAccrue alt.FolicurRallyNon-treated33

Summary• Reduce disease pressure throughoutseason to DELAY and REDUCE RATE ofepidemic• Early control measures key– Thorough pruning, timely first spray, delayedpruning• Mid- and late-season sucker control• Pristine and Quintec applications duringburr and cone development

ContactinformationDavid GentUSDA-ARSARS3450 SW Campus WayCorvallis, Oregon97331Phone: 541-738738-4167Cell: 541-231231-35843584gentd@onid.orst.edu

2007 Powdery Mildew Epidemic504540Disease incidence (%)3530252015105028-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep

Mechanical ‘Crowning’

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