Mr. Ludlow: Cut it out.
Spraying Plums for Brown Rot.
PROF. E. C. STAKMAN, MINN. EXP. STATION, UNIVERSITY FARM, ST. PAUL.
The brown rot of plum is without doubt one of the important limiting factors in plum-growing in Minnesota. In seasons favorable to its development, losses of from twenty to fifty per cent. of the crop in individual orchards are not uncommon.
Experiments on the control of the disease have been carried on by the sections of "Plant Pathology and Tree Insects and Spraying," of the Minnesota Experiment Station, since 1911. No accurate results could be obtained in 1912 and 1915 on account of crop failure in the orchards selected for experiment. Results are available for the years 1911, 1913 and 1914.
Brown rot is caused by a fungus (Sclerotinia cinerea (Bon.) Wor.). Every plum grower knows the signs of the disease on the fruit. Blossoms, leaves and twigs may also be affected. The diseased blossoms become brown and dry, and fall from the tree; the diseased leaves become brown and may die. Young twigs may also be killed.
Infection may occur at blossoming-time. The amount of blossom blight depends very largely on weather conditions; in fairly warm, moist weather there is usually more than in drier weather. The same is true of the rot on the fruit; during periods of muggy weather it may spread with amazing rapidity. The rot does not usually attack the fruit until it is nearly or quite ripe, although green plums may rot, especially if they have been injured. It is important to know that a large percentage of rotted plums have been injured by curculio. Counts have shown that in many cases as much as eighty-five per cent. of the rot followed such injury.
Rotted plums should be destroyed for two reasons: (1) The spores produced on them may live during the winter and cause infection in the spring; (2) if the mummies fall to the ground, late in April or early in May of the second spring the cup fungus stage may develop on them. This cup fungus produces a crop of spores capable of causing infection.