Fungous Diseases of Colorado Crop Plants ii 
Downy Mildew. —This disease has become increasingly 
abundant in Colorado, since it was first noticed in 1906. However, 
it has not become serious, except in a few localities. The leaves at 
tips of branches are usually attacked, turning yellow-green or yel¬ 
low-gray to purple. A fuzzy growth develops on the under side of 
the leaf, which is grayish at first, and later violet. 
Control .—Do not irrigate excessively. Do not crowd plants, 
as it makes them more liable to attack. 
Leaf Spot. —The disease first attacks lower leaves. Diseased 
spots are local, brown to black or yellow, circular, and with irregular 
edges (Plate I). Affected leaves usually turn yellow and drop pre¬ 
maturely. The trouble occurs in both old and new fields, and under 
very different soil conditions. 
Control .—Since alfalfa leaf spot is widespread and easily dis¬ 
seminated, control-measures are not entirely satisfactory. If dis¬ 
ease is serious, mowing of infested field when leaves begin to turn 
yellow will hold the disease in check. 
APPLE. 
Fire Blight. —See Pear, page 34. 
Apple Rot—Black Moi.d. —The fruit is attacked usually at 
the blossom end. Spots are formed which at first are small, dark 
purple-brown, and slightly sunken (Plate II). Affected tissue is 
Plate II. Apple rot or black mold. 
not greatly softened. In severe cases the apple becomes a shriveled, 
dark-brown mass. When the apple is placed in storage, the spot 
increases in size, and sometimes involves the entire fruit. The dis¬ 
ease often gains entrance to the fruit by means of wounds. Fre¬ 
quently, no external evidence of the trouble is noticeable, but when 
