56 
ANNUAL REPORTS OF DEPARTMENT OF 
In this area Marquis wheat, which is extremely susceptible to rae 
stem nisi now prevalent in the spring wheal area of the United States, 
has been grown for several years because of its rust resistance. It is 
significant, therefore, that Marquis is not susceptible to the races of 
rust thai were identified from rusted grains collected in southern 
Mexico. Of the nine different races found in northern Mexico, all 
were subsequently found in the United Stat 
CONDITIONS FAVORED NORTHWARD MOVEMENT OF RUST IN* 1938 
Stem rust was first observed in Texas in the spring of L938 on Febru- 
ary 2 al College Station. It was later determined that a scattering of 
rust had appeared in San Antonio and other sections of southern and 
centra] Texas at about the same time. Near San Antonio there was 
considerable early grain, and, as a result of excessive rainfall, rust 
became abundant fairly early in the season. 
During the period May 3 bo 5, and again on May 17 and 18, south 
wind- arc believed to have been responsible for spore showers in Okla- 
homa, Kansas, Missouri, and western Illinois. On dune 5 -pore- were 
trapped as \';\v north as Fargo, N. Dak., and on June 15 infection was 
observed on wheat in wesl -central Minnesota and at Brookings, S. Dak. 
While there was considerable variation in the amount of rust that 
developed in different localities in Kansas, Missouri, and Nebraska, 
t'ni- area produced an abundance of inoculum which appears to have 
contributed materially to the epidemic that developed later in States 
farther north. By exposing spore traps daily at certain representative 
points throughout the Mississippi River Valley it was possible to 
determine just when spore showers occurred. 
Table 10 shows the estimated number of spores trapped at repre- 
sentative points in the Great Plains region during 24-hour periods on 
the dates indicated. 
Table LO. Estimated numbers of spores trapped at representative point* in Ute 
Grail Plains region, 1938 
Place 
May 16 
May IS 
May '21 
May 25 
June 13 
June 14 
Okl khoma City, Okla 
1,296 
432 
3,382 
96 
l. 140 
95,616 
192 

- Q 
Beatrice. Nebr.I - 
Dallas, Tex 
Madison. Wis 

St. Paul, Minn 
g is 
- 3 
3 
, InWl 
Brookings, s. Dak 
Fargo, \". Dak 
There was a period from May L6 to 25, inclusive, when conditions 
favored the northward movement of rust. Again, on dune i:> and L4, 
south winds carried an abundance of inoculum into Northern States. 
Unlike the epidemic in L937, when rust spreading from the South 
reached into Illinois, Indiana, and even western Ohio, the epidemic 
this year moved more in a northwesterly direct ion. eventually causing 
considerable damage as far west as eastern Montana. 
Although more than L60 physiologic races of the stem-rust fungus 
have been identified during the past L5 years, race 56 was primarily 
