THE CONTROL OF TOMATO LEAF-SPOT 
11 
Tomato plants from a seed bed infested with Septoria should not 
be used. The cost of healthy plants is little in comparison with the 
extra loss that would result from the use of diseased seedlings. 
If the seed bed is infested by Septoria, it should be sterilized or 
abandoned. Full directions for sterilizing seed beds are published 
in Farmers' Bulletin 996 (0), a copy of which may be obtained 
by writing to the Department of Agriculture, Washington, D. C. 
The development of Septoria and the infection of tomato seedlings 
with leaf -spot can often be prevented in the seed bed by immersing 
the seed for five min- 
utes in a solution 
consisting of 1 part 
of bichloride of mer- 
cury to 3.000 parts of 
water and washing it 
for 10 minutes in 
running water and 
by spraying the 
plants two or three 
times with Bordeaux 
mixture before they 
are set in the field. 
ROTATION OF CROPS 
Growing any crop 
continuously or even 
frequently on the 
same piece of land 
usually results in an 
accumulation of its 
diseases. Eotation of 
crops, however, hin- 
ders their develop- 
ment, for the para- 
sites which infect one 
crop seldom are able 
to attack another. 
When a parasite can 
grow and sporulate 
on several different 
species of plants, all 
of these hosts have to 
be kept off the land for several years or the rotation will have little 
effect. Even if tomatoes are grown on the same piece of land only 
once in five years, the leaf-spot fungus will be ready to attack the 
next tomato crop in full force if horsenettle, jimsonweed, or other 
hosts are allowed to flourish there. 
Since this fungus can grow and sporulate on dead cornstalks, the 
use of corn in rotation with tomatoes has certain disadvantages. If 
the cornstalks remaining on the field are not thoroughly plowed 
under at the end of the season, they may become infected by the 
fungus, especially if tomatoes, horsenettles, or jimsonweeds are grow- 
ing in adjoining fields. This would result in its rapid multiplica- 
tion. The effect of growing tomatoes after corn in this case is 
Fig. G. — Potato leaf infected by Septoria lycopersici 
