New pathogenic races of flax rust have been responsible for the 
precipitous rise and fall in the popularity of flax varieties. 
During the last 20 years losses due to flax rust have ranged from 
0.5 to 10 percent, or from $200,000 to $12,000,000. A rapid build- 
up of races attacking Bison resulted in heavy losses in the North- 
Central States in 191, 192, and 1943. By 19h rust-resistant 
varieties had replaced most of the Bison, and rust losses were of 
minor importance. Races attacking Dakota, a variety grown throughe~ 
out the North-Central States, were discovered in the Red River Valley 
of Minnesota and North Dakota in 1948. These new races spread so 
rapidly and caused such damage in 1950 and 1951 that by 1952 ruste 
resistant varieties had superseded Dakota in the main seed=flax- 
growing area of Minnesota, North Dakota, and South Dakota, and 
losses due to rust were small. 
Losses from pasmo have not exceeded 1 percent of the total flax 
crop except in 193, when the loss was estimated at 5 percent. 
Pasmo usually does not infect the plant heavily until it is approach- 
ing maturity. It is prevalent throughout the flax-growing area, but 
is more severe in southwestern Minnesota, southeastern North Dakota, 
and eastern South Dakota. 
Wilt was formerly a very destructive disease throughout the flax- 
growing area of the North Central States, but in this area during the 
10-year period losses did not exceed 1 percent in any year as a 
result of the growing of resistant varieties. It was more destructive 
in Minnesota and eastern North and South Dakota. Losses from stunt- 
ing and premature ripening due to wilt may vary from 0.5 percent in 
cool seasons to 2 or 3 percent in warm years. 
A number of seed-borne and soil-inhabiting fungi cause seedling 
blights and damping-off of flax, reducing stands. Seed lots con- 
taining many broken or cracked seeds or seeds of weak germination 
are most subject to damage. Many seed lots respond to treatment, 
Consequently, loss attributable to seedling blight and damping-off 
includes the cost of treating the seed, the seed that must be sown 
to compensate for the reduced stand due to the disease, and the 
reduced yield due to thin stands. This loss may range from 0 to 2 
percent or more each year. 
Hops 
Downy mildew of hops occurs in Washington, Oregon, California, and 
New York. Hop culture in New York has been practically eliminated, 
largely because of the mildew disease. The disease is most critical 
during periods of high humidity and less serious in the drier valleys 
of hop production. The diseased leaves and vines are deformed, and 
hop cones sre not formed or are unsalable. The annual losses amount 
to $1,541,000, or about 5 percent of the total hop production in the 
country. About 10 percent of the crop in Oregon, h.5 percent in 
California, and less than 1 percent in Washington is lost. 
