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Effect of Amendments and Fungicides on Aphanomyces Root Rot of Peas. G. C. Papavizas, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; J. A. Lewis, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:215-220. Accepted for publication 23 September 1970. DOI: 10.1094/Phyto-61-215.

Cruciferous amendments such as leaves and stems of cabbage, kale, and mustard at 0.5% of the oven-dry weight of soil, gave a considerable reduction of the root rot of peas caused by Aphanomyces euteiches in the greenhouse. Kale was also effective in the field. Several NH4-N sources (NH4Cl, NH4OH, NH4HCO3, NH4NO3), urea, and 20:20:20 fertilizer greatly reduced root rot severity in the greenhouse. Hydrated lime, S, and several Na and Ca sources (NaNO3, Na2CO3, Ca cyanamide) were ineffective. Attempts to control the diseases with the nonvolatile fungicides 2-(3-thiazolyl)benzimidazole, 2,6-dichloro-4-nitroaniline (Botran), methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate (benomyl), and zinc ethylenebis (dithiocarbamate) (zineb) failed. Only the fungicide p-dimethylaminobenzenediazo sodium sulfonate (Dexon) was effective in the greenhouse and in the field at 100 ppm. Very good control of A. euteiches was obtained in both greenhouse and field with methylisothiocyanate (MIT) and other fungicides that decompose to MIT in natural soil. Sodium N-methyldithiocarbamate (metham), 3,5-dimethyl-tetrahydro-1,3,5,2H-thiadiazine-2-thione (DMTT-I, dazomet), DMTT-II (Micofume, a dazomet formulation), and DMTT-III (Plant Bed Fumigant, a dazomet formulation) controlled root rot effectively in the greenhouse and field at 50-200 ppm. These fungicides were effective with several pea cultivars and at a soil temperature range of 17-32 C. Lower concentrations of these materials were required to suppress root rot when the soil containers were closed in polyethylene bags for 2 weeks after fumigant application than when left uncovered.