Keltamuumiotaudin tarttuvaisuudesta sekä sen ehkäisemisestä Paration-valmisteilla

Abstract

The significance of fruit lesions of different kinds in brown-rot infection has been investigated. M. fructigena conidia were rubbed with a paint brush on the surface of apples uninjured and injured in different ways. All the uninjured fruits remained healthy. Slight injury done by copperlime 0.5 % (Cuprosan 3) and smallish spots, without cracking of the fruit, due to apple scab (Venturia inaequalis) were also unfavorable to the penetration of the brown-rot fungus. Infection in the former case was 0 %, in the later 7.1 % of apples inoculated. The inoculation of apples with severe corking and cracking resulted in 20.0 % infection and the inoculation of fruits injured by the codling moth (Carpocapsa pomonella) in 75.0 % respectively. All the fruits were infected when conidia were placed in a wound made with a knife-blade. It is thought that the susceptibility of lesions of different kinds to the brown-rot fungus is chiefly due to the moisture of the substrate and the air in the immediate proximity of the growing hypha. Spraying with the usual fungicides appears to be successful in controlling the brown-rot disease only if every fresh wound is covered (12). The control of apple scab and codling moth is also of importance, to avoid lesions made by these. It was thought that a compound penetrating the fruit tissues might be effective in controlling the disease through inhibiting the growth of mycelium in the tissues. One such chemical penetrating the plant tissues is diethylnitrophenylthiophosphate (E 606) (6). Parathion is found to inhibit the growth of Sclerotinia fructigena conidia (1). The fungistatic action on the brown-rot fungus of Parathion and some other chemicals penetrating the fruit tissues was investigated in the laboratory by dipping apples of the variety Charlottenthal or soaking them for 24 and 48 hours in the liquids. Every treatment consisted of 6 apples. Table 2. shows the daily growth of the brown-rot spot on apples treated in different ways and inoculated. The growth rate is shown in figure 2. Dipping, which corresponds in effect to one spraying (6), in 0.1 % mercuric chloride and in 0.1 % Cheminova-Parathion retarded the growth of the fungus. Soaking for 24 hours in Parathion reduced the growth greatly, soaking for 48 hours made the growth poor. Soaking in 0.05 % copper sulphate, 0.5 % tannin, 1 % ferrous sulphate and 0.1 % hydroquinone, too, retarded the growth of the fungus. The observations indicate that Parathion possesses an obvious fungistatic action on the brown-rot fungus and is possibly efficient in controlling it. For this reason a preliminary spraying experiment was carried out in 1950. The results indicate that Parathion was the preparation most successful in controlling the disease. This is due to the fungistatic action of Parathion and also to its insecticidal properties. Further investigations are needed into the significance of Parathion compounds in the control of the brown-rot disease.