Studies on the chemical control in dormant stage of diseases of fruit trees. Preliminary report. I

Effect of dormant sprays against the black spot disease of Japanese pear, caused by Alternaria Kikuchiana TANAKA. 1

Abstract

Experiments were made on dormant spray for the control of black spot disease (Alternaria Kikuchiana) of Japanese pears by means of spore formation test in vivo, spore germination test in vitro and spraying experiment in the field.
Sprays used were of the following: Bordeaux mixture, lime sulfur, mercury fungicide (Riogen), sodium pentachlorophenate (PCP-Na), mixture of sodium pentachiorophenate and lime sulfur (LS-PCP-Na), and mixture of pentachlorophenol and machine oil emulsion (Oil-PCP).
(1) The mixture of lime sulfur and sodium pentachlorophenate (LS-PCP-Na), showing much more effect in retardation of both spore germination in vitro and spore formation on the disease spots of twigs, was more effective in the field experiments than single spray of these two chemicals.
(2) Each of Riogen, sodium pentachlorophenate (PCP-Na) and the mixture of pentachlorophenol and machine oil emulsion (Oil-PCP), being little effica-cious to retard spore germination, but showed remar-kable effect in retarding spore formation and also in the field experiments.
(3) Lime sulfur, usually applied as a dormat spray, being an ineffective remedy against spore germination in vitro and spore formation in vivo, showed little effect in controlling the disease in the field.
(4) The Bordeaux mixture was superior both in retarding of spore germination and in adhesiveness to any other fungicide, but was inferior in retarding of spore formation, and it showed no marked effect in the field experiments.
(5) Results of the present experiments led the authors to conclude that strong fungitoxicity and good penetration are requisite to dormant spray for efficient control of the black spot disease, while adherence is not so important.