Field Guide for Integrated Pest Management in Hops

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may allow nearby infected plants to remainin the hop yard. Several plants adjacentto symptomatic plants should also beremoved. If possible, plants to be removedshould be treated in late summer with asystemic herbicide, such as glyphosate, tokill roots. Sites should be allowed to layfallow for one season so that remainingliving roots will produce shoots that canbe treated with herbicide. Soil fumigationmay also be helpful in killing infected rootpieces that remain after roguing if largerareas are affected.Precautions should be employed tolimit spread within a hop yard and betweenyards. The use of contact herbicide forspring pruning is preferable to the use ofmechanical mowers that may transmit theviroid. Similarly, removing basal vegetationlater in the season by chemical rather thanmechanical means also reduces the riskof transmission. Thorough washing offarm equipment to remove plant residueand sap may help reduce the likelihoodof transmission to new fields. Treatingknives and cutting tools with a disinfectantsolution for 10 minutes may reducetransmission. Many products includingbleach (sodium hypochlorite), calciumhypochlorite, and hydrogen peroxide havebeen suggested but results are inconsistent.31ABOVE RIGHT: Figure 49. Reducedgrowth and sidearm development ofWillamette due to Hop stunt viroid.(D. H. Gent)AT RIGHT: Figure 50. Prominentyellow speckling along and betweenleaf veins associated with infection byHop stunt viroid. (D. H. Gent)
32Other Viruses, Viroids, and Virus-like AgentsKenneth C. Eastwell and Dez J. BarbaraAt-A-GlanceOther Viruses,Viroids, andVirus-likeAgents◆◆These virusesand viroids donot merit controlat this time, butgrowers shouldbe aware ofsymptoms.◆◆Use of virusandviroid-freeplanting stockis a first line ofdefense.◆◆Some of theseviruses areproblematic inEurope and/orother countries,but are notcurrently an issuein the U.S.Several virus and viroids are knownto occur in hops that are not addressedby current management practices in thewestern United States. However, growersshould continue to be vigilant for theappearance of symptoms that may indicatethe presence of one of these agents.Hop latent viroidThe group of sub-viral hop pathogensthat contains Hop stunt viroid also includesHop latent viroid. The presence of Hoplatent viroid has been confirmed in mosthop-producing regions of the worldincluding the United States; wherever it isknown to occur, it is widely distributed.Hop latent viroid has a very limited naturalhost range so the primary source of newinfections is the use of infected propagationmaterial or mechanical transmission fromother hop plants. Infection by Hop latentviroid does not cause overt symptoms onmost varieties, but it can reduce alphaacid production up to 20% in the limitednumber of symptomless varieties that havebeen studied. The variety Omega is sensitiveto Hop latent viroid (Fig. 51) and infectedplants of this variety express obvioussymptoms including general chlorosis, poorgrowth, and retarded development of lateralbranches. Total alpha acid production ininfected Omega plants can be reduced by50 to 60%. The epidemiology of Hop latentviroid is still not totally clear but controlmeasures adopted elsewhere have centeredon producing viroid-free hops and plantingaway from sources of infection such as olderplantings.Apple fruit crinkle viroidAnother sub-virus pathogen, Applefruit crinkle viroid (AFCVd) was firstreported to occur in hops in Japan in 2004.This viroid is not known to occur in NorthAmerica in either its hop or fruit tree hosts.Very little additional information is availableabout this viroid in hops. Symptoms arereported to be very similar to those inducedby Hop stunt viroid and appropriate controlmeasures are similar (see Hop stunt viroid,preceding two pages).Figure 51. Yellowing of leaves and weakgrowth of Omega variety caused by Hoplatent viroid. The pathogen is widespreadin hop yards in the U.S. but symptomsare rarely produced on varieties currentlygrown in the U.S. (D. Barbara)Arabis mosaic virusReports of the hop strain of Arabismosaic virus appeared in early literature ofthe U.S. hop industry. However, recentattempts to identify infected plants failedto detect the presence of this virus incontemporary hop production in the UnitedStates. Arabis mosaic virus is transmitted bya nematode, Xiphinema diversicaudatum,which has a very limited distribution in theUnited States. The absence of the nematodevector and the adoption of new varietiesbred in the United States have contributedto the apparent elimination of Arabismosaic virus from current U.S. productionareas. In the United Kingdom, where thenematode vector is indigenous, infectionby Arabis mosaic virus is reported to reduceyield by 23% to 50%. Arabis mosaic virusis also transmitted by introducing sap frominfected plants into mechanical wounds,but this is thought to be an insignificantroute of virus spread. Plants infected withArabis mosaic virus can display a diversity ofsymptoms depending on variety, weather,
Page 3 and 4: AcknowledgementsFunding for this ha
Page 5 and 6: Use pesticides with care. Apply the
Page 8 and 9: Monitoring for Pests, Damage, and T
Page 10 and 11: Active IngredientTable 1. Signal Wo
Page 13 and 14: 8At-A-Glance:AlternariaCone Disorde
Page 15: 10At-A-Glance:DownyMildew◆◆Sele
Page 18 and 19: 13sporangiophores emergewith sporan
Page 20 and 21: Fusarium CankerDavid H. GentFusariu
Page 22 and 23: Gray MoldDavid H. GentGray mold gen
Page 24 and 25: 17 19to infection, and their develo
Page 26 and 27: PERCENT DISEASED LEAVES100806040200
Page 28 and 29: Sclerotinia Wilt (White Mold)David
Page 30: Verticillium WiltDavid H. Gent and
Page 33 and 34: 28At-A-GlanceCarlavirusComplex◆
Page 35: 30At-A-GlanceHop stuntviroid◆◆U
Page 39 and 40: 34 NematodesAt-A-GlanceHop CystNema
Page 41 and 42: 36 Arthropod and Slug Pest Manageme
Page 43 and 44: 38 Hop AphidAmy J. DrevesAt-A-Glanc
Page 45 and 46: 40 Garden SymphylanAmy J. DrevesAt-
Page 47 and 48: 42 Hop Looper and Bertha ArmywormJi
Page 49 and 50: 44ABOVE: Figure 78. Adult black vin
Page 51 and 52: 46 Twospotted Spider MiteJim D. Bar
Page 53 and 54: 481412108642025AVERAGE MITES PER LE
Page 55 and 56: 50 SlugsAmy J. DrevesAt-A-GlanceSlu
Page 57 and 58: 52 Beneficial ArthropodsDavid G. Ja
Page 59 and 60: 54 Predatory Lady BeetlesWashington
Page 61 and 62: 56A generalizedsummary ofthe season
Page 63 and 64: 58 Predatory BugsThe predatory bugs
Page 65 and 66: 60Assassin BugsReduviidaeDescriptio
Page 67: 62 Parasitic Wasps(Parasitoids)At-A
Page 70: Long-legged FliesThese small to med
Page 73 and 74: 68At-A-GlanceSpiders◆◆Spiderpre
Page 75 and 76: 70 17Planning a WeedManagement Prog
Page 77 and 78: 17 72Figure 161. Redroot pigweedpla
Page 79 and 80: 17 74Figure 177. Common mallow. (R.
Page 81 and 82: 76Calculating Treated Acres versus
Page 83 and 84: 78Figure 198. Severe cupping of lea
Page 85 and 86: 80Figure 210. Yellowing anddeath of
Page 87 and 88:
82HHarmonia axyridis 55Hemerobius s
Page 89:
84TTablesTable 1 5Table 2 12Table 3
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Field Guide for Integrated Pest Management in Hops

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