34 
BULLETIN 759, U. S. DEPARTMENT OF AGRICULTURE. 
plants were known to exist within a 5 -mile radius the results have 
been included. 
Table VIII. — Summary of data of plat tests to determine whether leaf-spot can 
he prevented on alfalfa sown in isolated localities by the superficial steriliza- 
tion of alfalfa seed. 
State and town. 
Date 
sown. 
Date 
visited. 
Area 
(square 
rods). 
Distance 
to nearest 
alfalfa 
(miles). 
Leaf-spot. 
Maine: 
1915. 
June 2S 
1916. 
May 6 
June 
1916. 
June 14 
Sept. 12 
...do 
1 
20 
40 
1 
2 
40 
40 
40 
40 
10 
40 
40 
40 
40 
40 
40 
40 
6 
? 
§ 
5 
5 
10 
i 
5» 
8 
12i 
10" 
10 
5 
Albion 
Do. 
Fairfield 
Do 
May 20 
June 1 
May 
June 
May 20 
June 
May 
June 
Sept. 5 
...do 
Sept. 6 
Sept. 12 
Aug. 11 
Oct. 2 
Oct. 4 
...do 
Do 
Doubtful 
Vassalboro 
Do 
South Dakota: 
Do 
Wisconsin: 
Doubtful 
McConnor 
Radisson 
Do 
Merrill 
Do '.. 
...do 
...do 
Oct. 2 
...do 
Do. 
Do 
Do 
...do 
...do 
Do 
Tomahawk 
...do 
...do 
Do. 
Do 
Weirgor 
...do 
...do 
...do 
Oct. 5 
Do. 
Do. 
From Table VIII it appears that the one small well-isolated plat 
started in 1915 did not develop leaf-spot until the following year. 
Of the 16 plats started in 1916 only 2 failed to show an abundance 
of leaf -spot in the autumn of the same year. One of these plats, 
located at Harrison, Me., was in very poor condition, only a few 
scattering spindling plants about 4 inches high being found. How- 
ever, other plats in almost as poor condition showed leaf-spot. The 
second doubtful plat, at Doering, Wis., was in very vigorous con- 
dition, but it had been cut just previous to inspection, leaving very 
little foliage. Unfortunately, it was not feasible to revisit the plat 
the following year. 
These results are in accord with previous experiments and experi- 
ence. Surface sterilization of seed apparently accomplishes nothing 
in excluding leaf -spot from alfalfa fields. But these results do point 
very clearly to one conclusion, that the leaf -spot fungus is not car- 
ried on or in debris mixed with the seed. The greenhouse experi- 
ments, which are only suggestive because of their limited extent, 
indicate that the fungus is not carried within the seed. 
Thus, in conclusion, it is necessary to say that no positive evidence 
pointing toward the method by which this disease gains access to 
remote alfalfa fields has been found. Evidence has been obtained 
which apparently eliminates other plants previously under suspicion 
as host plants of the fungus from consideration as sources. A lim- 
