Agronomic and Economic Responses of Spring Wheat to Management of Fusarium Head Blight.

Spring wheat (Triticum aestivum) crop losses in the Red River Valley of Minnesota and North Dakota caused by Fusarium head blight (FHB) epidemics incited by Fusarium graminearum are common. Fungicide application is often recommended when environments promote disease development but benefits have not been fully evaluated when environment, cultivar resistance, and economic outcome are considered. Agronomic and economic characters were determined for cultivars with various resistance levels when treated with no fungicide; propiconazole at 63 g active ingredient (a.i.)/ha applied at Feekes growth stage (FGS) 2, tebuconazole at 126 g a.i./ha applied at FGS 10.51, or propiconazole at 63 g a.i./ha applied at FGS 2 followed by tebuconazole at 126 g a.i./ha applied at FGS 10.51. Revenue returned from FHB moderately susceptible (MS) cultivars was 8% greater than moderately resistant (MR) cultivars in low-disease environs but differences were not significant when disease was moderate. Deoxynivalenol accumulation in grain of MS and MR cultivars was unchanged by fungicide treatment. MS cultivars were economically more adventitious to grow than MR cultivars in both disease environments.

Region and Field Level Distributions of Aster Yellows Phytoplasma in Small Grain Crops.

Aster yellows (AY), a disease of small grain crops caused by aster yellows phytoplasma (AYp), produces disease symptoms similar to barley yellow dwarf (BYD). From 2003 to 2005, small grain production fields in Minnesota and North Dakota were surveyed to determine the incidences of AY and BYD. In-field spatial patterns of AY-infected plants also were investigated. Plants collected along a five-point transect line were tested for AYp using nested polymerase chain reaction (PCR) and quantitative real-time PCR assays, and extracted plant sap was tested for serotypes PAV and RPV of Barley yellow dwarf virus (BYDV) using enzyme-linked immunosorbent assays. During 2003, 2004, and 2005, AYp was detected in plants from 49, 15, and 7% of tested fields, respectively, whereas BYDV was found in plants from 2, 0, and 5% of fields, respectively. Average amplicon count number indicated an in-field spatial trend for greater incidence of AYp and increased populations of AYp in plants located near field edges, with comparably low copy numbers at transect point locations toward the direction of field center. AY is likely a common but largely undetected disease on small grain crops in the Upper Midwest.