Fungous Disi:ases of Colorado Crop Plants 
0 / 
Control .—Affected branches and badly affected trees should be 
destroyed. 
Fire Blight. —See Pear, page 34. 
Crown Gall. —See Apple, page 12. 
Shot TdoLE. —See Cherry, page 26. 
Black Knot. —Early evidence of infection is indicated by a 
slight swelling of the branch. This is followed by a rapid increase 
in size. The knot attains its full size in 10 to 12 days. As growth 
increases, the bark ruptures and exposes a granular olive-green 
growth. Later this mass turns black (Plate XI, Fig. i). Knots 
vary as to size and shape, some being only a quarter of an inch in 
length, while others attain a length of five or more inches. As a 
rule, they do not encircle the entire branch. Diseased twigs are 
often curved. The knots persist on old twigs and the next year they 
produce new knots. Old knots remain on trees for 5 or 6 years. 
Control .— (i) All knots should be removed, by cutting at 
least 6 inches below the diseased portion, and destroyed. 
(2) Spraying with Bordeaux mixture, 4-5-50 formula, just 
before the buds open, has been recommended. 
POTATO. 
Early Blight. —This potato trouble is not prevalent in Colo¬ 
rado. The leaves become spotted in July or August, about the time 
the blossoms appear. The small brown spots are surrounded by 
concentric rings, which give them a very characteristic appearance. 
The spots may run together, causing withering and death of the en¬ 
tire leaf. As a result of the leaf affection, tubers do not develop nor¬ 
mally. The tubers, however, are not diseased. 
Control .— (i) Spray with Bordeaux mixture. This should be 
done at intervals of about two weeks. The first application is made 
before the appearance of the disease. 
(2) Plant resistant strains. 
(3) Maintain the vigor of the plant by proper methods of cul¬ 
tivation. 
Scab (Oospora). —This “Oospora scab,” so prevalent in east¬ 
ern states, has never been serious within the state. The most com¬ 
mon scab on potatoes in Colorado is due to another fungus— Rhisoc- 
tonia. “Oospora scab” is a surface disease of the tubers. The fun¬ 
gus produces a roughened, pitted, scabby surface (Plate XII). It 
also occurs on beets, cabbage, and other plants. 
Control .— (i) Use smooth, scab-free tubers for seed. 
(2) Disinfect seed potatoes. Soak the tubers for two hours in 
formalin, i pound (pint) in 30 gallons of water. 
