CHLOROSIS OF TREES

Chlorosis is a condition of the leaf in which chlorophyll fails to develop normally. BOURCART (1) states that this pathological condition is known as jaundice when caused by want or excess of water, and chlorosis when it is due to lack of iron or potash. An excess of carbonate of lime in the soil, insufficient nourishment, defective condition of the roots, a pathological condition of the whole tree, are some of the many causes which may produce chlorosis. When due to lack of iron, chlorosis has some analogy to the anemia of man. Much has been published on the causes and treatment of chlorosis. No attempt is made to cite all the literature published, but a few citations are given to indicate the extent of its occurrence, and its treatment. BOURCART (1) states that an excess of carbonate of lime is the predominating cause of chlorosis of trees with seed pips, such as the pear, and more especially of the vine. He recommends green vitriol for both trees and vineyards. KELLEY (7) found that an excess of manganese in the soil was responsible for the chlorotic condition of pineapples, as well as some other plants in Hawaii. JOHNSON (6) confirmed KELLEY'S finding and found that chlorotic pineapples were restored to normality by spraying with an iron sulphate solution. WALLACE and MANN (8) found considerable difference in the chemical composition of the ash of chlorotic and normal fruit trees. The percentage of ash in the dry matter, with one exception, was higher in the chlorotic than in the normal leaves. The Chemistry Department of the Idaho Agricultural Experiment Station (5) associates the chlorosis of trees and shrubs with high calcium carbonate soils even though a considerable amount of iron is present. GILES (3) found that the chlorosis of pineapples in Porto Rico was the result of malnutrition, caused by an excessive amount of calcium carbonate in the soil. GILES and CARRERO (4) report that chlorotic rice plants may be restored to their normal color by spraying with ferrous sulphate. BURGESS and POHLMAN (2), in studying the cause of citrus chlorosis, found that improper irrigation was a factor. Spraying the trees with an iron salt solution did not give beneficial results.