Getzin, Louis W.

Yencho, G. C.

Undetermined

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Section IMites and Sap-Sucking InsectsECONOMIC INJURY LEVEL AND POPULATION DEVELOPMENTSTUDIES OF THE PEA APHID ON GREEN PEASG. C. Yencho and L. W. GetzinWestern Washington Research and Extension Center, Puyallup, WA 98371MATERIALS AND METHODSField studies to determine an economic injury level for the pea aphid inwestern Washington were conducted during 1983-1984. Four experimentsconsisting of two 0.11 ha plantings of 'Puget Variety' peas per season'were conducted. Each experiment consisted of 12 treatments and 6 replications. Various aphid densities, simulating those in commercial plantings were established and population development was monitored weeklyThe relationship between accumulated aphid feeding days, and pea yieldand quality components at harvest, was determined.RESULTS AND DISCUSSIONAphid population development in experimental plots typically approximatedan exponential growth curve. Population development in 1983 was characterized by an early migration of aphids into experimental plots, a rapidincrease to 72.4 aphids/plant (A/P) at bloom time in control plots and adecline to 1.7 A/P at harvest due to an Erynia neoaphidis epizooticPopulation development was delayed in 1984. At bloom time aphid populations in control plots averaged 1.8 A/P. At harvest, approximately 21days post bloom, populations averaged 135.4 A/P. Large differences inthe temporal positioning and magnitude of peak aphid densities were probably a result of environmental conditions and mortality factors presentprior to, and during the growing season. A mild winter and cool, moistsummer in 1983 were probably largely responsible for early aphid migration and the occurrence of an epizootic, respectively. Environmentalconditions during summer 1984 did not promote the occurrence of anepizootic.A model relating accumulated aphid feeding days (ACCAFD) to crop loss wasderived for 1983 and 1984. The model is as follows:9Y=a + bx1 + cxj + dx2where Y is yield in kg/ha, x1 is ln(ACCAFD), and x9 is tenderometerlevel, a measure of pea maturity. The constants a, b, c, d are derivedstatistically. Based on this model, a tentative economic injury level ofca. 95 ACCAFD has been calculated. Action thresholds for the pea aphidat bloom time were determined by regressing yield on average A/P at bloomtime. Action threshold levels of approximately 10 A/P and 1 A/P werecalculated for 1983 and 1984, respectively. Differences in these valueswere probably largely a result of growing season differences rather thantemporal changes in aphid stress. These values are preliminary and further validation is required.

Economic Injury Level and Population Development Studies of the Pea Aphid on Green Peas

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Economic Injury Level and Population Development Studies of the Pea Aphid on Green Peas

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