Barley Yellow Dwarf Impact on Wheat Yield.

Barley yellow dwarf virus (BYDV) is one of the most important viral diseases of wheat (Triticum aestivum L.) in the world. Current action thresholds used to manage the aphid complex that vectors BYDV and cereal yellow dwarf virus (CYDV) in many Midwestern states, including Wisconsin, were developed in the 1970’s. Since this time Midwest agriculture has seen dramatic changes in winter wheat cropping systems (rotation and acreage shifts), yield potential, and integrated crop and pest management strategies. In fall of 2007 we proposed a series of experiments designed to improve the current action threshold for aphid vectored BYDV and CYDV in Wisconsin.  Three winter wheat varieties (Truman and Pioneer 25R47 BYDV susceptible; INW0316 BYDV resistant) were planted conventional till at three planting dates (9/14, 9/28, and 10/23) and (9/17, 10/5, and 10/19) at Arlington and Lancaster WI, respectively. Each variety received four aphid management treatments: (i) untreated control, (ii) seed-applied insecticide (imadicloprid), (iii) spring applied foliar insecticide (Lambda - cyhalothrin) applied at first in-field detection of aphids, (iv) fall followed by spring foliar insecticide (Lambda - cyhalothrin) applied at first in-field detection of aphids. The experimental design was a randomized complete block split-plot design with four replications. The whole plot factor was planting date whereas the sub-plot factors were variety and aphid management strategy. Twenty flag leaves were sampled from each plot at Feekes 10.5 (inflorescence completely emerged) to quantify the level of BYDV/CYDV infection using the multi-plex virus detection PCR method.  Visual disease incidence and severity of BYDV/CYDV infections were also quantified on a 0-5 scale. At physiological maturity grain yield and seed mass (g 1000^-1 kernels) were quantified.  Results of this experiment will be presented at the 2008 ASA meetings.