Field Guide for Integrated Pest Management in Hops

Monitoring for Pests, Damage, and Treatment SuccessThe concepts of acceptable pest levels, economicinjury levels, and economic thresholds implya need to monitor for levels of pests or pest damagein relation to these levels. Monitoring is fundamentalto IPM because it is used to objectivelydetermine the need for control and also to assessthe effectiveness of control after action has beentaken. Sampling and monitoring requires the abilityto identify pests, pest damage, and key naturalenemies of pests, as well as knowledge of pest andnatural enemy biology and life history. In monitoring,the grower or a scout takes representative samplesto assess the growth status and general healthof the crop, the presence and intensity of currentpest infestations or infections, and the potential fordevelopment of future pest problems. Monitoringmay take many forms such as presence/absence orcounts of pests from visual inspection of plants orplant parts or traps placed in or around fields (e.g.,sticky traps, pheromone traps, spore traps). Samplingshould be conducted to provide a representativeassessment of the pest population in all areas tobe similarly treated, such as part of a field, a singlefield, or adjacent fields. Various sampling schemeshave been developed to assist in monitoring efforts.Monitoring an area for environmentalconditions (especially temperature and relativehumidity) that are favorable or unfavorable for pestdevelopment is also important. This includes theuse of models (e.g., the powdery mildew risk index,degree-day for downy mildew spike emergenceand spider mites) to forecast conditions conduciveto disease or pest development, and surveying thearea for the presence of alternate hosts of hop pests(e.g., agricultural or ornamental varieties of prunethat might harbor overwintering hop aphids) andnatural enemies (e.g., flowering weeds that providehabitat for natural enemies).Monitoring, when conducted routinely—at least weekly during the growing season—andin combination with good record keeping andawareness of model forecasts, can help determinetrends in pest and natural enemy populationgrowth over time. This assists in planning forpest management decisions and assessing theeffectiveness of control actions.Check theAgWeatherNetwebsite at URLhttp://weather.wsu.edu/ foravailable diseaseand pest models.Consult withlocal experts forinformation on usesand limitationsof pest forecastmodels in IPM.3Multi-tactic Management ApproachesWhen prevention is not effective or possibleand monitoring indicates that a pest population hasreached or exceeded an action threshold, interventionis required to lower pest numbers to acceptablelevels. For any given pest situation, pest/crop managerswill need to choose one or more appropriateand compatible management tactics. The basictypes of controls are mechanical, biological, andchemical.Mechanical controls include simple handpicking,erecting barriers, using traps, vacuuming,and tillage to disrupt pest growth and reproduction.Tillage is commonly used to manage weeds inhop, and can be important in managing arthropodpests such as the garden symphylan.Biological controls are beneficial organismsthat prey on or parasitize pests, or organisms thatdo not damage crops but compete with pests forhabitat and displace pests (e.g., Bacillus pumilus forpowdery mildew management). Some biologicalcontrol agents are commercially available for releaseinto cropping systems (i.e., fields, greenhouses) innumbers that can overwhelm pests or that supplementexisting natural enemy populations. Addingagents to the ecosystem is referred to as augmentativebiocontrol; an example would be the releaseof predatory mites Galendromus occidentalis and/orNeoseiulus fallacis, which can be purchased and releasedfor management of twospotted spider mites.Natural enemy populations also can be augmentedusing commercially available chemical attractants,such as methyl salicylate. Biological control also canbe implemented by managing crops to conserveexisting natural enemies (conservation biologicalcontrol) through preserving habitat (includingalternative hosts and prey) necessary for normalnatural enemy growth and reproduction, or by usingmanagement tactics (e.g., selective pesticides orpesticide uses) that have minimal negative impacton natural enemies. In hop, biological control ismost widely practiced in the form of conservationbiological control through the use of selective pesticidesand modified cultural practices.Chemical controls include synthetic andnatural pesticides used to reduce pest populations.Many newer synthetic pesticides are much lessdisruptive to non-target organisms than older,broad-spectrum chemistries (e.g., organophosphate,carbamate, and pyrethroid insecticides). Insecticidesderived from naturally occurring microorganismssuch as Bacillus thuringiensis, entomopathogenicfungi and entomopathogenic nematodes, andnatural insecticides such as nicotine, pyrethrin,and spynosins are important tools in many organicfarming operations, and are playing larger roles innon-organic crop production. Selective pesticidesshould be chosen over non-selective pesticidesto preserve natural enemies and allow biologicalcontrol to play a greater role in suppressing pestoutbreaks. However, broad-spectrum pesticidesremain useful and necessary components of IPMprograms as measures of last resort when othermanagement tactics fail to maintain pests atacceptable levels.Photos Above: A. J. Dreves,D. H. Gent, D. H. Gent