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.

Spraying experiments, the summarized results of which are given here,
show that the disease can be fairly well controlled even in badly
affected orchards.

Some of the experiments were carried on in the orchards at University
Farm and some in commercial orchards. There were from twelve to
forty-five trees in each plot, and the trees on which counts were to be
made were selected before the rot appeared. The percentages given below
refer to fruit rot and do not include blossom or twig blight. The object
was to determine the times for spraying and the most effective spray
mixtures. Details are for the most part omitted, and the results of
various experiments are averaged.

For convenience the times of spraying ar