This peculiar condition attracted attention in Colorado apple orchards following the severe winters of 1898 and 1899. In 1901 it was particularly noticeable in several orchards of one locality in that state. What may prove to be the same trouble has subsequently been observed in California and Idaho. Records of apple - rosette have not come from any other sources, so that the disease seems to be limited in its geographical range. This fact alone accounts for the disease being considered as one of the minor troubles of the apple.
The rosette of apple is said to present an appearance suggestive of peach - rosette. The characteristic feature of the disease is the presence of a tuft or rosette of small leaves at the ends of branches; such branches are otherwise nearly destitute of foliage. Affected limbs and even whole trees die from the effects of rosette. In the spring the lateral buds die, and the terminal one develops a clustered branch on which the leaves are much more dense than they normally should be; whence the term rosette.
Apple-rosette is called a soil disease. No parasites of any kind are concerned. Like most diseases of this sort the true cause will probably remain in obscurity for some time to come. Conditions accompanying the disease are somewhat as follows: in an excess of marl and an adverse water-supply the tree sends out few or no fibrous roots. In fact the roots cannot penetrate this type of soil to any extent, consequently the tree has a shallow root-system, and the water-supply becomes inadequate. Accompanying these provoking conditions is winter injury, which comes about in the following way: the water may be in sufficient quantities in the early part of the season, but by the last of June the supply is exhausted. The soil readily dries out and the tree suffers from a lack of moisture; hence its growth stops and the tissues harden. In July water of irrigation is supplied and many trees start into growth again; the result is that such trees possess soft and immature tissues which with the advent of winter are killed or severely injured.
Our incomplete knowledge of the cause of the disease makes the problem of control difficult, or even impossible. The following recommendations based on the information at hand are offered: (1) avoid planting apple-trees in soil where marl is close to the surface; in this way shallow roots and an inadequate water-supply are avoided; (2) increase the depth of the soil by deep plowing before the orchard is planted, by the addition of straw and by plowing under green manures such as vetch, clover or rye; (3) water of irrigation should be used judi - ciouslv. The amount of water should be lessened with the approach of autumn in order that the tissues may properly harden before winter.
Paddock, W. Plant diseases of 1901. Apple tree rosette. Colorado Agr. Exp. Sta. Bul. 69: 6 - 9. 1902.