Management of powdery mildew and leaf spot diseases on winter wheat in Oklahoma

摘要

A field trial was conducted to determine efficacy of fungicides for managing powdery mildew (PM) and leaf spot diseases on hard red winter wheat (HRWW). Wheat was planted near Stillwater in a Norge loam soil. The test area was fertilized 20 Aug 2012 with 51 lb/A of 46-0-0 nitrogen in the form of granular urea. Conventional tillage was used and plots were sown 8 Oct at 90 lb/A with 'OK Bullet' HRWW seed treated with 2.4 fl oz/cwt Gaucho 600. Plot size was 20 ft long with 7 rows spaced at 7 in. Treatments were arranged in a randomized complete block design with four replications. Fungicides were applied with a CO_2 wheelbarrow sprayer as a broadcast foliar application using flat fan nozzles (8003EVS) spaced 18-in. apart and calibrated to deliver a volume of 20 GPA. Fungicides were applied 14 Mar (Feekes' growth stage (GS) 6), 29 Apr (GS 10.1), and 7 May (GS 10.5.1). PM severity was rated on 25 Apr (lower leaves). Leaf spot (LS) severity ratings were taken on 30 Apr. PM and LS severity was determinedby estimating the percentage of diseased leaf surface area on a scale of 0-99 (modified Cobbs' scale). The trial was harvested 12 Jun using a Hege small-plot harvester (model 125B). Harvested grain was cleaned using an Almaco seed cleaner, and grain moisture was determined using a Mini GAC Plus meter (Dickey-John Corp, Illinois). Yield (bu/A) and test weight (lb/bu) were determined for each treatment. Results were analyzed using SAS (version 9.1; SAS Institute Inc., Cary, NC), and means were separated by the least significant test (LSD) at a=0.05.