Clement, Steve L.

Elberson, Leslie R.

Young, Frank

Undetermined

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Section V.Cereal Crops PestsEFFECT OF TILLAGE, CULTTVAR AND CROPPING SYSTEM ON APHIDPOPULATIONS IN SMALL GRAINS OF CENTRAL WASHINGTONL.R. Elberson1, Steve Clement1 and Frank Young2^SDA-ARS, Western Regional Plant Introduction Station and2Land Management andWater Conservation ResearchUnitWashington State UniversityPullman, Washington 99164-6402509/335-3609elberson@mail.wsu.eduSpring-plantedwheat and barley support largernumbers ofcerealaphids than fall-planted grainsinWashington and Idaho (Elberson& Johnson 1995, Feng et al. 1991, Feng et al. 1992). Arequirement to significantlyreduce PM-10 emissions in the 7-15 inch rainfall zone ofcentralWashingtonmay result in a significant shift from fall to spring cropping systems under no-tillcultivation. Consequently, we are researching the potential increaseofaphid problems with thesemanagement practices.Research ObjectivesOurmainobjective is to quantifyand contrastcereal aphid populations in large repUcated on-farmplots at aRalston,Washington site over 5 years, thereby providing the first baseline informationon the frequency andoccurrence ofeconomicaphid populations in this agronomic zone. Theprimary aphid species that colonizeWashington wheat and barley are the English grain aphid(EGA), rose-grass aphid (RGA), greenbug (GB), bird cherry-oat aphid (BCOA), cornleafaphid(CLA), and the Russian wheat aphid (RWA) (Clement et al. 1990). In addition, aphidpopulations willbe related to action thresholds and the need for insecticide sprays to controleconomic populations. Our secondary objective is to identify and estimate the number ofnaturalenemies present in the Ralston plots and to evaluate their role in controlling economicallydamaging populations ofgrain aphids.MethodsSurvey sites consist of4 cropping systems:System 1. Winterwheat - fallow - winter wheat - fallow (soft white, Lewjain)System 2. Spring wheat - fallow - spring wheat- fallow (soft white, Alpowa)System 3. Spring wheat - spring wheat - spring wheat - spring wheat (hard red, Butte 86)System 4. Spring wheat - spring barley - spring wheat - spring barley (Butte 86 &Baroness)hiEach cropping system ispracticed in 2 plots and each plot isreplicated in 4 subplots (8 4mx139.4 m).Field preparation in 1996 included standard cultivation (C) and no-tillage (NT). All plots wereplanted into no-till cultivation in 1997.Plots were surveyed on 4 dates (1 and 30 May, 13 June, 2 July) in 1996 and 5dates in 1997 (6and 19 May, 10 and 26 June, 10 July). Following methods ofElberson &Johnson (1995), 10sampling locations per plot were selected bywalking azigzag pattern, stopping every 12-14 m.At each stop 10 tillers were randomly selected within 0.4 m2 and all aphids were identified andcounted.After apreliminary assessment of natural enemies on2 July of 1996 showed promise of naturalenemy impact, 1997 sampling was expanded to include estimation of aphid predators andparasites. Parasitoid mummies on 100 tillers per subplot were counted and transported to alabfor rearing and identification. Predators within each sampling area (0.4 m2) were counted andidentified asto life stage and species ifadult. The survey ofpredators wasnot limited to selectedtillersdue to the mobility ofadults.Crop growth stage was determined using the decimal code devised byZadoks et al. (1974).ResultsThe majority ofaphids recorded were RWAand EGA, with other species infrequently observed.RWA populations in 1996, first detected on 30May, wereapproaching or hadexceeded aneconomic threshold of 10% infested tillers (Pacific Northwest Insect Control Handbook) by 13June in Butte 86' spring wheatunderconventional tillage, requiring anapplication ofLorsban(recommended rate) in these plots on 19June (Fig. 1). EGA populations were first detected 1May and increased rapidly after mid-June (Fig. 3). However, bythenext sampling date (2 July)the grain had reached agrowth stage (soft dough development, Zadoks growth stage 85) tolerantofhigher populations and atwhich insecticide applications are notrecommended (Bishop et al.1986).RWA populations in 1997 were substantially less than the previous year (Fig. 2). EGApopulations in 1997 exceeded counts of 1996 in some plots (Fig. 4), howevernumbers did notreach economic thresholds until the softdough development stage asinthe previous year.Aphid predators were first recorded on 10 June in 1997 and parasitoids on26 June withhighestnumbers occurring on the last sampling date (Figs. 5-6). Predators and parasitoids werepresentin all subplots.48DiscussionIn 1996, spring wheat supported more RWA and EGA than winter wheat and, in general,conventional tilled plots supported more aphids than no-tilled plots (Figs. 1-2). RWA populationsexceeded the economic threshold in "Butte 86' springwheat under conventional tillage. TheRWA populations observed on 'Butte 86' under no tillageand 'Alpowa' spring wheat andXewjain' winter wheat under conventional tillage remainedbelow levels requiringinsecticideapplications. EGA populations in spring wheat of 1997were comparable to those of 1996 (Figs.3-4. Winter wheat of 1997 supported significantly more EGA than in 1996. Duringboth yearsEGA densities peaked during graindevelopment.Parasitoidswere identified asAphidius avenaphis (Fitch). Predators were identified in the field asHippodamia spp. andCoccinella septempunctata. A. avenaphisandHippodamia spp. areendemic species andC. septempunctata was introduced as partofthe biological control programforRWA. Although numbersofbeneficials were relatively low over the entire growing season,counts coincided with EGA population growth andmay be an important factor in controlling thisaphid species.ReferencesBishop, G.W., H.W. Homan and R. Johnston. 1986. Development and control ofthe Englishgrainaphid on wheat. University of Idaho Cooperative Extension Service Current InformationSeries No. 778.Clement, S.L., R.C. Johnson, and K.S. Pike. 1990. Field populations ofthe Russian wheataphid(Homoptera: Aphididae) and othercereal aphids on cool-season perennial grass accessions.Journal ofEconomic Entomology 83:846-849.Elberson, L.R. and J.B. Johnson. 1995. Population trends and comparison of sampling methodsforDiuraphis noxia and othercereal aphids (Homoptera: Aphididae) in northern Idaho.Environmental Entomology 24:538-549.Feng, M.G., J.B. Johnson, and S.E. Halbert. 1991. Natural controlof cereal aphids (Homoptera:Aphididae) by entomopathogenic fungi (Zygomycetes: Entomophthorales) and parasitoids(Hymenoptera: Braconidae andEncyrtidae) on irrigated spring wheat in southwestern Idaho.Environmental Entomology 20:1699-1710.Feng, M.G., J.B. Johnson, R.M. Nowierski, and S.E. Halbert. 1992. Population trendsandbiological aspects ofcereal aphids (Homoptera: Aphididae), and their natural mortality factorson winterwheatin southwestern Idaho. Pan-Pacific Entomologist 68:248-260.Zadoks, J.C., T.T. Chang, and C.F. Konzak. 1974. A decimal code for thegrowth stages ofcereals. Weed Res. 14: 415-421.49Mean %infestedtillers12108642Lorsban treated (19 Jun)t T1.0.o I 1 I I• 1-May• 30-MayD13-Jun• 2-JulP1 P3 P5 P6 P7 P8(C) (C) (C) (NT) (C) (NT)(WW) (SW) (SW) (SW) (SW) (SB)Plot(Tillage)(Treatment)Figure 1. Russianwheat aphid infestations in Ralston plots, 1996.1210-8-6420• • -• 6-May• 19-MayD10-Jun• 29-JunDIO-JulMean %infestedtillersP2(WW)P4 P5 P6 P7 P8(SW) (SW) (SW) (SB) (SW)Plot(treatment)Figure 2. Russian wheat aphid infestations in Ralston no-till plots, 1997.50Mean %infested 15tillersLorsban treated (19-Jun)P1 P3 P5 P6 P7 P8(C) (C) (C) (NT) (C) (NT)(WW) (SW) (SW) (SW) (SW) (SB)Plot(tillage)(treatment)Figure 3. English grain aphid infestations in Ralston Plots, 1996302520Mean% *"infested 15tillers Art1050P2 P4 P5 P6 P7 P8(WW) (SW) (SW) (SW) (SB) (SW)Plot(treatment)Figure 4. English grain aphid infestations inRalston Plots, 199751• 6-May• 19-May• 10-Jun• 26-Jun• 10-Jul1.5Mean no.parasitoids 1per subplot0.5• 6-May• 19-May• 10-JunB26-Jun• 10-JulP2 P4 P5 P6 P7 P8(WW) (SW) (SW) (SW) (SB) (SW)Plot(treatment)Figure 5, Parasitized aphidson SampledTillers in Ralston Subplots, 19972.52-Mean no. 1.5coccinellidsper subplot 10.5• 6-May• 19-May• 10-Jun• 26-Jun• 10-JulP2 P4 P5 P6 P7 P8(WW) (SW) (SW) (SW) (SB) (SW)Plot(treatment)Figure 6. CoccinellidPredators in Ralston Subplot SamplingLocations, 199752

Effect of Tillage, Cultivar and Cropping System on Aphid Populations in Small Grains of Central Washington

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Effect of Tillage, Cultivar and Cropping System on Aphid Populations in Small Grains of Central Washington

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