INFLUENCINC} CONDITIONS. 18 



woatluM' may start an opidiMnic tliat will destroy the entiri' crop of 

 certain varieties, provided the fungus is present. 



MoUfKve. — Moisture is not onlj" necessary for the germination of 

 the spores, but it favors the growth of the fungus and hastens spore 

 production. In a moist atmosphere the spores are produced much 

 njore rapidly than when the air is dry. Moreover, rain is an active 

 agent in the spread of the disease, splashing the spores from an 

 atiected apple to adjacent healthy fruits. Heavy dews followed l)y 

 hot cloudy days with a humid atmosphere appear to make ideal con- 

 ditions for the rapid develoiHuent of this disease. 



Temperature. — The fungus causing this disease is decidedly a hot- 

 weather fungus and rarely is a serious pest north of latitude 40^ N. 

 »Iuly, August, and September are the three bitter-rot months, and a 

 maxinunn temperature near W^ F. for several days in succession, 

 coupled with suitable moisture conditions, is necessar}' to start a 

 serious outbreak. Infection of some fruits may take place as early 

 as the middle of June," but the fungus grows slowly and fruits s]);ii-- 

 ingly until the warmer weather of July increases its rate of develop- 

 ment. In Virginia, on Julv !<•, itM».>, the writer observed bitter-rot 

 spt)ts covering a (piarter to half of the apple. One specimen was 

 somewhat more than half invohed in rot, and the numerous rings of 

 spore masses indicated that the fungus had been fruiting abundantly 

 lor days, and the infection had doubtless taken place a couple of weeks 

 earlier. The variety was Yellow Newtown, and the fruit was scarcely 

 more than half grown. The proper combination oF heat, moisture, 

 and an abundance of spores may not occur until August or Septem})er, 

 or in some seasons not at all. 



The fungus is so Intiuenced l)y the heat of the sun, and perhaps by 

 the light also, that the fruit on the south side of a tree ma}' become 

 badl}^ affected before the disease is noticeal)le on the opposite side. 

 Stin^on * observed this fact, and in the Virginia orchards the writer 

 found that almost invariably the fruit on the sunny side was destroyed 

 first, and oftentimes a portion of the crop on the north side would 

 escape when the destruction was complete on the south side. This 

 held true not only in the particular orchard under experimentation, 

 but in many orchards visited during the outbreak of 1903, and during 

 the past season as well. Moreover, it was observed that fruit on the 

 inside lower branches well protected from the sun was less attacked 

 and often escaped when that on exposed portions of the same tree was 

 destroyed. Owing perhaps to exposure to the sun there was a con- 

 siderably higher percentage of rotten fruit on trees partly defoliated 

 with leaf-spot fungi than in the case of trees with full foliage. Not 

 onlv is the fruit on the sunny side of the tree worse affected, but the 



«See Burrill and Blair, Bui. 77, 111. Agr. Exp. Sta., p. 332. 

 &Bul. 1, Missouri State Fruit Experiment Station, p. 6. 



