Application Methods Influencing the Effectiveness of Carboxin for Control of Common Bunt Caused by Tilletia tritici and T. laevis in Spring Wheat. D. A. Gaudet, Crop Sciences Section, Agriculture Canada Research Station, Lethbridge, AB T1J 4B1. B. J. Puchalski, and T. Entz. Crop Sciences Section, and Statistics, Agriculture Canada Research Station, Lethbridge, AB T1J 4B1. Plant Dis. 76:64-66. Accepted for publication 4 July 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-0064.

The concentration of carboxin was determined on individual seeds of seed lots of the bunt-susceptible spring wheat cultivar Laura obtained from different seed treatment operators, farmers, and the manufacturer. These seeds were subsequently infested with a composite of teliospores of virulent races of Tilletia tritici and T. laevis and seeded in irrigated and dryland sites in 1989 and 1990. At mean bunt infection levels of 19.2 and 50.0%, which occurred in 1990, failure to achieve target rates of carboxin of 550–690 mg/kg in seed appeared to be the greatest cause of poor efficacy. At low mean disease incidence in the nontreated check (7.5% in 1989), or when the mean carboxin concentration exceeded 466 mg/kg of seed, the mean percent control, averaged over seed lots, was high (>90%). At mean carboxin concentrations below 446 mg/kg in 1990, however, control averaged only 63.8%. There was no relationship between mean percent control and mean carboxin concentration at carboxin rates below 446 mg/kg in 1990 or between variability in mean percent control and variability in mean carboxin rates. Failure to achieve target rates and random variability within the seed microenvironment are important factors affecting the efficacy of carboxin at higher disease incidence levels and may explain the lack of consistent control of common bunt with this fungicide.

Keyword(s): Vitavax.