INSECT AND FUNGOUS ENEMIES OF THE APPLE. Pal 
young spots are very small and often show purplish or reddish mar- 
gins, but under favorable conditions they rapidly enlarge, involving 
the entire apple in decay. The disease extends inward toward the 
core at about the same rate as the spread on the surface, forming a 
cone-shaped area which can be easily crushed out with the fingers. 
Owing to the shrinking of the invaded tissues, the spots become 
somewhat sunken, and this distinguishes it from black rot and brown 
rot. Several spots, or, in severe cases, several hundred spots, may 
occur on the same apple, although one spot is sufficient to destroy 
the whole fruit. 
CAUSE OF THE DISEASE. 
Bitter rot is caused by the fungus Glomerella rufomaculans 
(Berk.) Spauld. and Shrenk, which invades the tissues of the apple, 
producing the familiar spots described above. It passes the winter 
in cankers on the limbs and in mummied fruits. Under favorable 
weather conditions spores from these sources and perhaps from un- 
known sources infect the fruit, starting an outbreak of bitter rot. 
When the germ tube, resulting from the germination of a spore, finds 
its way through the skin of the apple, it immediately begins to branch 
and grow rapidly, obtaining its food supply from the tissues and 
causing these to die and turn brown. After a time clusters or tufts 
ef fruiting branches are formed and these burst through the skin in 
rings, producing pink masses of spores which serve to spread the dis- 
ease to other apples. Millions of spores are produced from a single 
spot, so that under favorable conditions the entire crop of an orchard 
may become diseased from one center of infection. 
In addition to the summer spores or conidia, there are produced on 
the mummied fruits and in limb cankers winter spores or ascospores, 
which constitute the perfect stage of the fungus. It is not definitely 
known that these ascospores play any important part in the lfe 
history of the fungus. 
THE LIMITING FACTORS. 
Barring preventive measures, the two limiting factors determining 
bitter-rot outbreaks are weather conditions and varietal resistance. 
Heat and moisture are essential to the vigorous growth of the fungus, 
and of these two heat is the more important. While hot, showery, 
or muggy weather is ideal for the development of the fungus, serious 
outbreaks of the disease may occur during comparatively dry 
weather, provided the temperature is high and the dews are heavy at 
night. 
Infections may take place at any time during July, August, and 
September, but rarely earlier or later. High summer temperatures 
are required for the rapid growth of the fungus, and these are the 
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