54 
IOWA ACADEMY OF SCIENCE 
July will mean a decaying potato crop, unless some successful method of 
checking this rapidly developing fungus is employed, and contrariwise, a dry 
midsummer will insure freedom from its ravages. 
The Potato Rot fungus {PTiytopJitJiora infestans) was' abundant in Iowa in 
1903; along with this mildew many of the other downy Mildews were common 
like Downy Mildew of the Grape (Plasmopora Yiticola) destrowing many of the 
young shoots and even berries of such grapes as the Noah, Yitis riparia, Lindley, 
etc. The Sunflower Mildew {Plasmopora Halstedii) was abundant on many com- 
posites like the Sunflower, Boot Jack and Marsh Sunflower {HeliantJius) . The 
years 1900, 1902 were unfavorable for the development of these fungi. These 
conditions are best shown by the conditions of the rainfall brought out in tables 
accompanying this paper. 
Mr. Norton^^ says, in speaking of late blight of potato, “This disease is not 
commonly destructive in Maryland, as the summer temperature is not usually 
sufiiciently low for a time long enough for the development of the parasite, 
though it has caused serious loss in many parts of the United States since 
1840, and has been destructive at times as far south as Florida, being no doubt 
introduced on northern seed.” 
Fusicladium and Monilia. H. Mueller-Thurgau^® in a paper on the Monilia Dis- 
ease of branches of Drupaceous Fruits, attributes the epidemic in Switzerland, 
of that year, to the cold days of March, 1900. In other words the frost was 
partly responsible for this disease in that branches became less resistant to 
the Monilia and allowed the fungus to enter easily. 
Rudolph Aderhold^* in a discussion of the development and life history of 
the relationship of Cladosporium and Fusicladium spores, and the causes that 
lead to infection thinks that the most favorable temperature for the germina- 
tion of Fusicladium pyrinum is +2° C. and germination is very energetic at 11°. 
The optimum. temperature of the same is 22°, but beyond this there is a rapid 
decline. Therefore the warm days of spring appear to be especially favorable 
for the germination of the spores of Fusicladium. The spontaneous appearance 
of Fusicladium is dependent largely upon the character of the weather, especially 
moisture, frequent rains are favorable. 
SOME FUNGUS EPIDEMICS. 
Mildews. It may be interesting to note here that in some years certain 
species of mildews are particularly destructive to certain host plants. 
Salmon^® states that the mildew of the cultivated hop sweeps in epidemics 
over some of the European countries in certain years, not appearing in inter- 
vals between. 
Mr. David Griffiths records an interesting observation of the occurrence of 
fungi. Beginning with 1892 E. communis was not found on Polygonum, a new 
host, in South Dakota until 1895, when some immature specimens were found 
in the northern part of the state. The following year it was more frequent 
and two years later abundant everywhere. Doubtless the fungus occurred in 
small quantity, though unobserved, previous to 1896. 
‘‘^Norton, J. B. S. Irish Potato Diseases. Bull. Md. Agr. Exp. Sta. 108 ;69. 
^^Schweiz. Zeitsch. f. Obst-Und-Weinhau. 1900. Centralb. f. Bact. u. Par. 2 Abst. 
<6:653. 
-^Landw. Jahrb. 29:541-587, pi. 9-12. 
«Torr. Bot. Club 9: 11. 
