Feb., 1907.] 
Phytophthora and Plasmopora. 
81 
fungus is employed, and, contrariwise, a dry summer will insure 
freedom from its ravages.” 
Professor L. T. Jones * reports upon a favorable season for 
potato late blight in Vermont: ‘‘In 1902, the weather was re¬ 
markably cool and moist up to about August 1st, and it has con¬ 
tinued cool and moist with more than the usual amount of rain¬ 
fall since.” That year we found the first Phytophthora July 13, 
‘‘the earliest date in a dozen years’ observations.” 
In 1903, Dr. Halsted f again reports serious outbreaks of 
rot in New Jersey, and mentions moisture as essential to this 
development of Phytophthora and states ‘‘A second favoring con¬ 
dition is warm weather—not hot or cold, but a condition of the 
atmosphere which obtains when there is a week or month of show¬ 
ery summer weather, often spoken of as close or “muggy”— 
just such as we have experienced throughout the state during 
August. ” 
In this same connection Dr. Halsted gives the mean monthly 
temperatures and rainfall for New Jersey during the 15 years 
previous to 1903. These show for 1903 a June mean of 64.0° 
(-5.5°), July 73.3° (-0.6°) and August 68.4° (-3.9°) with rainfall 
about double the mean for June, normal for July and 2.32 inches 
in excess of normal for August. These conditions of 1903 fol¬ 
lowed a cool summer in 1902. Without closer analysis of these 
data we may now turn to other sources. 
Scribner J summarized the conditions favoring the disease as 
follows: 
“1. Humidity—The years of great outbreaks have always 
been years of excessive humidity.” 
“2. A temperature ranging from 65° to 75° F.—a few de- 
grese above 74° will check the development entirely, and down 
to 45° F. the fungus will continue to grow.” 
“3. Moisture in the soil—hence a clayey soil or one that 
will retain moisture is more favorable to rot.” 
While we may always need to keep in mind the distinction 
between Phytophthora rot, and certain other forms of rot, we 
may pass to a statement of Dr. Galloway’s|| “The rapid spread 
of the disease is dependent in a large measure upon eertain con¬ 
ditions of moisture and heat. A daily mean, or normal temper¬ 
ature of from 72° to 74° F. for any considerable time, accom¬ 
panied by moist weather, furnisher the best conditions for the 
spread of the disease”; on the other hand, if the daily mean or 
normal temperature exceeds 77° F. for a few days the develop- 
* Report Vermont Exp. Station: 15:210: (1902). 
t Report New Jersey Exp. Station: 1903: 541-555. 
i Report Section of Veg. Path., U. S. Dept. Agric. 1888: 338. 
Galloway, B. T.—Some destructive potato diseases—Farmer’s Bull. 15: 1894: U. S 
Dept. Agric. 
