Cone, Wyatt W.

Wright, Larry C.

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Section 1Mites and Sap-Sucking InsectsA PRESENCE-ABSENCE SAMPLING PLANFOR THE TWO-SPOTTED SPIDER MITE ON HOPSL.C. Wright and W.W. ConeWashington State UniversityRt 2 Box 2953-AProsser, WA 99350-9687Sixteen hop yards were sampled for mites from 20 June through 24 August 1989.Twenty five vines were sampled per yard in 14 of the yards and 10 vines in twoyards. One mainstem leaf was sampled at each of the 0, 1, 2, 3, 4, and 5 mheights from each vine. Mite eggs, immatures plus adult males, adult females,and predators were counted on each leaf under a 9X binocular microscope.Mean height of mites increased from 1 to 2 m in mid June to 3 to 3.5 m in midJuly. Mean height stayed at 3 to 3.5 m from mid July until sampling ended.The linear relationship between In mean and In variance (Taylor's power law)was used to calculate a presence-absence sampling plan for adult females mites.The plan is based on adult females because they are easier to see than eggs andimmature mites.To sample a hop yard for mites, werecommend walking through the yard ina diamond-shaped pattern, selectingvines approximately at random, andpicking one main stem leaf per vine atthe mean height of the mites. Examineeach leaf for the presence of adultfemales and record your findings.Recording the presence of predators isalso important. After each sample,compare the total number of infestedleaves with the figure at right. Ifthe total number of infested leavesfalls between the two lines, takeanother sample. If the total is lessthan the lower decision line, stopsampling and take no control action.If the total is greater than the upperline, stop sampling and apply a control,per leaf is used as an example,been established.20 30 40 80 80 70 90Number of Lacvm Sampled100Presence-absence sequential samplingplan for adult female two-spotted spidermites on hops (P • 0.05).A control threshold of 10 adult femalesThe economic threshold of mites on hops has notThis is a preliminary sampling plan based on one year's data. We plan to collectdata next summer to complete the sampling plan. A similar sampling plan for thehop aphid has been finished and we hope to combine the plans.

A Presence-Absence Sampling Plan for the Twospotted Spider Mite on Hops

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A Presence-Absence Sampling Plan for the Twospotted Spider Mite on Hops

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