Submitted to: Fungicide and Nematocide Tests
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2005
Publication Date: 2/20/2006
Citation: Paulitz, T.C., Scott, R.B. 2006. Effect of seed treatments for control of rhizoctonia root rot in spring wheat, 2005.. Fungicide and Nematocide Tests. 2006. Vol. 61:ST014. Interpretive Summary: Under high Rhizoctonia conditions, a number of seed treatments improved seedling health, but did not result in yield increases.
Technical Abstract: An experiment was conducted on the USDA-ARS Palouse Conservation Field Station north of Pullman, WA on a Thatuna silt loam, pH 5.9 and 3.86 % O.M. The site was naturally infested with both R. solani AG-8 and R. oryzae, based on previous tests. No-till plots were direct-seeded with spring wheat in 2003 and winter wheat in 2004. Plot size was 8 ft X 24 ft. Seed treatments were applied to seed in a total liquid volume of 10 fl oz/cwt. The experiment was arranged in a randomized complete block design with four blocks. Volunteer crop and weeds were sprayed with Roundup Ultramax II (24 fl oz/A) 2 days before planting, and rattail fescue was spot-treated with Surefire (24 fl oz/A rate) 2 days after planting. All plots were planted with spring wheat cv. ‘Louise’ on 10 May 05 with a no-till plot drill at 1.5 in depth. Liquid fertilizer was applied in-furrow at seeding (130-10-20 lb/A of N-P-S). Five seedlings were randomly harvested from each of three locations per plot on 3 Jun 05. Stand count, plant height, numbers of tillers, number of seminal roots and number of crown roots were counted on each plant. To quantify infection, percent incidence of crown roots with symptoms of Rhizoctonia infection (speartipping, brown root tips, constricted lesions) was determined on each plant. Plots were harvested on 7 Sep 05 with a small plot combine. Data were analyzed by ANOVA and means were separated by least significant difference test. Seminal root data were analyzed using Kruskal-Wallis One-Way Nonparametric ANOVA. In 2005, the yield of spring wheat was low because of minimal winter precipitation (5.8 in. below 30-year average for Nov-Feb) and reduced stored water in the soil profile. Non-treated seed had the lowest numerical yield, but not statistically significant from treatments. All treatments except Raxil XT alone significantly increased seedling height. Treatment with Raxil XT or Raxil XT + Poncho 600 significantly increased tiller number, as did one of the Raxil +Allegiance + L0121 combination treatments. Plants that developed from the nontreated seed had numerically the lowest number of seminal roots and the highest percent infected seminal roots, although the means for these variables were not significantly different among treatments. All treatments except Raxil XT alone and Dividend Extreme significantly reduced the root rot rating of seedlings. These results indicate that seed treatments can improve seedling health, but the effects on seedlings may not always result in significant increases in yield.