BORDEAUX INJURY AS INDUCED BY RAIN FALL (PRELIMINARY REPORT)

Abstract

Potted plants of several sorts, such as persimmons, peacnes, Japanese pears, American grapes, beans, soy-beans, and Azuki-beans, were sprayed with Bordeaux mixtures of 6-1.5-100, 6-6-100, or 6-18-100, After spraying, a half of each treat ment was brought into glass house and the other half was left on in the field. After rain fall Bordeaux injury appeared on the leaves of sprayed plants left in the field, but no injury occured on the plants under glass so far as they stay there. After they had taken out in the field, Bordeaux injury appeared similarlly on them. The injury was severest on the plants sprayed with 6-1.5-100 Bordeaux and slightest on the plants sprayed with 6-18-100 Bordeaux. Some plants sprayed with hydrated lime only were free from injury.
Persimmon leaves were painted with 6-6-100 Bordeaux. The injury was induced on the leaves whose both surfaces or upper surface only were painted. No injury was induced on the leaves whose lower surface only was painted. The leaves reversed after being painted the upper surfaces only were also free from the injury.
As the results of the above experiments seemes to indicate that Bordeaux injury is induced after the sprayed surfaces were wetted by the rain water, the sprayed surfaces of persimmons and buckwheat were wetted artificially with reserved rain water, and after this treatmente for 14-24 hours, typical Bordeaux injury was observed on the wetted surfaces of the sprayed leaves.
These facts are favourable to the assumption that the rain fall induces Bordeaux injury on the sprayed leaves of plants.
It seems that the rain water is necessary to solubilize the copper in the Bordeaux mixture and solubilizing action of the rain water is a little stronger than that of the distilled water, as the injury on the plants wetted with the former is severer than that on the plants wetted with the latter.