Eradicant action of fungicides applied to dormant peach trees for control of brown rot (Monilinia fructicola)

There is evidence to suggest that the eradication of Monilinia fructicola in infected peach peduncles in winter may reduce brown rot during the subsequent season. In a series of experiments, in which treatments were applied in the field and the results assessed in the laboratory, benomyl and arsenic or mercury compounds were more effective in suppressing sporulation from overwintering infections than any of the other materials tested. Benomyl effectively suppressed sporulation from infected peach peduncles and mummified peach fruits and was not phytotoxic. Sodium arsenite was an effective eradicant of M. fructicola in peach peduncles and mummified peach fruit at 0·1% and 0·3%, but it was phytotoxic to both peach and apricot trees at rates as low as 0·01% whether applied in mid-winter or at early bud-swell. Phenylmercury chloride (PMC), mercury acetimide at 0·06% Hg and phenylmercury dimethyldithiocarbamate at 0·015% Hg were effective eradicants. At lower rates the mercurials were unsatisfactory. No phytotoxicity was observed following dormant applications of the mercury compounds.

Lime-sulphur plus oil was the best of the remaining materials. DNOC performed about as well as lime-sulphur on peduncles but failed to suppress sporulation on mummified fruits and was occasionally phytotoxic.

Sodium pentachlorophenate was superior to pentachlorophenyl acetate at the same rate, and, in contrast with some overseas experience with peaches and apricots, was not phytotoxic in these tests.

Bordeaux mixture, fentin acetate, N.C.I584, captan, captafol and dichlone, although not phytotoxic, did not show significant eradicant or antisporulant action.

There was some evidence that PMC acted both as an eradicant and an antisporulant.