Influence of Fungicide and Chemical Salt Dip Treatments on Crater Rot Caused by Rhizoctonia carotae in Long-Term Storage. Mark D. Ricker, Research Associate, Campbell Institute for Research and Technology, Campbell Soup Company, P-152 R5, Napoleon, OH 43545. Zamir K. Punja, Associate Professor, Centre for Pest Management, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6. Plant Dis. 75:470-474. Accepted for publication 23 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0470.

Nine fungicides and two chemical salts were tested for their ability to reduce mycelial growth of Rhizoctonia carotae on V8 agar. Among the fungicides, only sodium orthophenylphenate (SOPP, Dowcide A) and mancozeb (Dithane M-45) completely inhibited growth and were fungicidal. Benomyl, chlorothalonil, and iprodione also inhibited mycelial growth but were fungistatic. The fungicides captan, dicloran, thiabendazole, and thiophanate methyl reduced growth of the fungus by 4–85% of that in unamended agar. Two chemical salts, potassium carbonate (K₂CO₃) and sodium bicarbonate (NaHCO₃), at 0.1 M totally inhibited growth of R. carotae and were fungicidal. Potassium carbonate was also fungicidal at 10 mM. The fungicides SOPP, benomyl, thiabendazole, and iprodione, the salts K₂CO₃ and NaHCO₃, and hot water treatment (58 C), were evaluated alone or in various combinations for disease control on carrot cvs. Danvers 126 and Gold King over 4 yr of storage trials. A dip treatment (1 min) of naturally infected carrots was made before an 18- to 24-wk storage period, or 4 wk after trials were initiated. The most effective treatment (52–70% reduction in disease incidence over 4 yr) was SOPP, used either alone or in combination with 0.1 M K₂CO₃. Treatments applied after 4 wk in storage were as effective as those made after harvest. The addition of K₂CO₃ to the SOPP solution maintained a high optimal pH; the combined cost of the treatment was about 30–40¢ per metric ton.

Keyword(s): Daucus carota, storage rot.