Effect of seed disinfection and delayed sowing on the control of bunt in infested soil

The results of 4 years' experiments on the control of bunt (Tilletia spp.) in wheat sown in artificially infested soil are presented. New Improved Ceresan was superior to the other standard seed disinfectants tested. When applied at 3 ounces per bushel it reduced infection 66.3 and 74.8%, based on infection in the untreated checks as 100%. A 3-ounce rate sometimes caused a marked reduction in stand. Bunt was reduced 47.5 and 52.3%, by 1/2-ounce and 1-ounce rates of application, respectively. There was no consistent loss in effectiveness when the seed was treated 3 weeks before sowing. Ethyl mercury iodide was about equal to New Improved Ceresan when the grain was sown 24 hours after treating, but there was a distinct decline in effectiveness when 10 days elapsed between treating and sowing. Copper carbonate and copper sulfate were equally effective in controlling infection by spores in the soil. Copper carbonate reduced bunt in the crop 22.3 to 31.5% in the 4 years. Results in one year indicated that under certain conditions formaldehyde may be as effective as copper carbonate and copper sulfate, but in two other years formaldehyde reduced infection only 4.4 and 10.3%. Percentages of bunt were significantly lower when the wheat was sown the day the soil was inoculated and watered than when sown a week or 10 days later. Under the conditions of this experiment, between soil inoculation and sowing 50 to 60 days usually were required before sufficient spores were destroyed to eliminate danger from heavy infection. Low temperatures, however, occasionally prevented heavy infection. Low percentages of infection were obtained in untreated checks sown 60 days or more after the soil was inoculated with bunt spores. The seasonal trend in bunt infection in treated and untreated wheat was very similar.