Limited control is obtained by the use of dusts and sprays, and 
their use is absolutely necessary in regions of high humidity. 
Control measures save some of the crop; however, there are also 
vine losses which are high because expensive hop-yard structures 
are not utilized until a new vine can be brought into production 
2 years after planting. Dusting and spraying cost about $15 per 
acre in Oregon, where many applications are required, to a minimum 
of about $7.50 in areas where the disease is less severe. Although 
there is some varietal difference in susceptibility to the disease, 
the type of hop most in demand is susceptible. 
Oats 
The losses from oat diseases in the United States are generally 
higher than those from diseases of other small grains, because most 
of the crop is spring-growmm in warm, humid regions usually favorable 
for disease development. Heavy losses are also experienced in the 
deep South, where oats are fall sown and the winters are mild and 
humid. However, less than half of the more than 20 diseases attack- 
ing oats in the United States have caused appreciable damage. 
Crown rust, the most important disease, occurs throughout the oat~- 
growing areas. It caused an average loss of 5.1 percent to the oat 
crop in the United States, and losses in Iowa have run as high as 
20 percent or more in some years. Individual fields may be a come 
plete loss. Losses vary from year to year, depending on weather 
conditions and abundance of inoculum of races of the organism that 
can attack the varieties of oats being grown. Crown rust does not 
cause damage in the less humid sections of the West. Both yield 
and feeding quality of the grain are reduced. 
The losses from the two Helminthosporium diseases, leaf blotch and 
Victoria blight, averaged 3.8 percent for the 10-year period, but 
were very severe in 196, 197, and 1948, when varieties susceptible 
to the latter were being grow. Since that time there has been 
very little loss. These diseases cause blighting of seedling and 
adult plants. Production in Iowa was reduced more than 30 percent 
in 197. 
Septoria black stem of oats first caused appreciable damage in Iowa 
and other North Central States in 1947. By 1952 it was widespread 
throughout the more northern States in this region and caused an 
estimated loss of 15 percent of the Iowa crop. 
Stem rust, like crown rust, occurs in the more humid sections and 
in the more humid years. Losses to individual fields during epidemics 
may be complete, but the average annual loss is much less than from 
crown rust. Stem rust was of minor importance after resistant 
varieties became generally available until the sudden increase in 
prevalence of race 7 starting in 1919. Race 7 caused heavy losses 
in Iowa, Minnesota, Wisconsin, and some other States in 1953, reaching 
10 percent in Iowa. 
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