Abstract
It is generally believed that the development of lime sulfur spray burn correlates with high temperature in the time of the application. In order to obtain further data on this correlation, a study was conducted during the summer of 1939.
Japanese pears, peaches, or American graped were sprayed with liquid lime sulfur from early morning till night at definite intervals. In the forenoon, temperatue and radiation gradually rised till noon when they stay nearly constant. Humidity falled rapidly after sun rise. In the early morning spray burn was very slight, and as the time advances it becomes more and more severe.
In the afternoon, the relation was reversed; later the afternoon, slighter the spray burn. After the sun sets, the sprayed leaves was scarsely injured. In relation to the temperature immediately after the application, denifite correlation of spray burn to high temperature was not secured, though there was high positive correlation when the forenoon or afternoon series were considered separately. As compared with the severity of the forenoon series at the same temperature, the severity of the afternoon series was always slighter. As well as with temperature, definite correlation of the severity of spray burn with humidity was not obtained. When intensity of radiation is above certain critical point, spray burn attain to its maximum and above thispoint injury did not increased. Below this point spray burn was roughly proportional to light intensity, and after the sun sets when radiation becomes nearly zero, it has hardly occured.
Lime sulfur of high concentration was applied on the upper or lower surfaces of some garden plants and the development of spray burn was observed. When lime sulfur was applied on the surfaces ofleaves, where no stomata existed, spray burn has never developed. When spray burn has developed, the sprayed surfaces had always stomata on them. So that it seems that the spray liquid penetrate thestomata through leaf tissues, where it attacks living cells and induces spray burn. If so, when stomata is closed, the spray liquid will not be able to penetrate into the leaf tissue and will not be able to cause spray burn. In relation to the foregoing experiments stomatal actvity was observed throughout the day. Close correlation between severity of spray burn and width of stomatal opening was obtained. Thus, the assumption that the stomatal activity regulates the lime sulfur spray burn may be partly acceptible, but needs further studies.
