Blackmer, J. L.

Halbert, Susan E.

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-9-Section 1Mites and Sap Sucking InsectsTHE BYDV CORN CONNECTIONS. E. Halbert and J. L. BlackmerSW Idaho K ( E Center, Parma, ID 83660Barley yellow dwarf virus (BYDV) epidemics have occurred in 4 out ofthe past 10 years in SW Idaho (Blackmer, 1986). Spread of the disease canbe reduced by delayed planting of fall grains and/or use of systemicinsecticides to control aphid vectors. But since protective measures arenot required every year it would be useful to be able to predict potentialfor epidemics.Although aphid numbers are important, potential for virus spread isalso contingent upon the percent of the aphids which are villiferous.The Idaho suction trap network is doing a satisfactory job of monitoringgrain aphid flights, but a means of monitoring primary inoculum pressureis needed. In England, an infectivity index (Plumb and Lennon) is used.This may be feasible on a limited scale in Idaho, but it is too laborintensive for statewide use. Because maturing corn was the most obvioussource of Rhopalosiphum padi. the most important BYDV vector in irrigatedgrain, experiments were conducted to ascertain whether percenttransmission by R. padi collected in corn was correlated with percenttransmission by R. padi in flight and on newly emerged grain.R. padi was collected from corn and grain in Prosser, Washington in1983, from corn, grain and a suction trap adapted for live collection inProsser in 1984, and from corn, grain and an adapted suction trap inCanyon County, Idaho in 1985 and 1986. All aphids were assayed for BYDVtransmission. Results are summarized as follows:Percent transmission of BYDV by R. padi collected on corn, grain or in asuction trap.Corn1 Grain2 Trap'WA 1983 11.5 14.I3WA 1984 0 3.23 7.2ID 1985 1.3 0.04 10 6ID 1986 0.6 1.33 6.91 All Morphs2 Alates only3 Wheat4 Barley - alate R. padi were very scarce on wheat in 1985 in Canyon CoID.-10-It appears from these data that a measure of the inoculum reservoirin corn could be a good predictor of primary inoculum pressure inirrigated areas.Blackmer, J. L. 1986. Relationship of aphid vectors to barley yellowdwarf epidemiology in southwestern Idaho. M.S. Thesis. Universityof Idaho, Moscow, ID. 90 pp.Plumb, R. T. and Lennon, E. 1982. Aphid infectivity and the infectivityindex. Report of the Rothamsted Experimental Station for 1981. Part1:195-197.

The BYDV Corn Connection

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The BYDV Corn Connection

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