THE CONTROL OF TOMATO LEAF-SPOT 9 
If pieces of the vines are left on the surface or so near the surface 
that they will soon become exposed, they will be likely to carry the 
disease over winter. Hence disking and plowing will not suffice 
unless the vines are completely covered. 
The practice of disking tomato land and sowing it to wheat or 
rye and grass in the fall enables the tomato leaf-spot fungus to. live 
over winter on pieces of dead tomato vines. Soon after the grain 
is cut it can pass to the dead stubble 3 and live over another winter. 
By the time the stubble is exhausted it will have plenty of dead 
grass leaves to subsist upon. Hence the fungus can live from year 
to year as a saprophyte under this system, as it has plenty of dead 
organic matter as food. Unless the tomato vines bearing the fungus 
are thoroughly covered by soil, this parasite will apparently con- 
tinue to flourish in tomato regions of the Middle Atlantic and Mid- 
dle Western States. 
The control of tomato leaf-spot by preventing the multiplication 
of the fungus rather than the infection of the plants is wholly a 
matter of field sanitation. Moreover, it requires no chemicals, no 
extra men, teams, or time, but merely a careful execution of a cus- 
tomary field operation. Its effect will depend on how thoroughly it 
is done and how commonly it is practiced. 
DESTRUCTION OF OTHER HOSTS 
The tomato leaf-spot fungus is capable of living on a considerable 
number of hosts. In addition to the common garden tomato Norton 
(5) succeeded in infecting eggplant (Solanum melongena) , purple 
thorn apple {Datura tatula), potato (Solanum tuberosum), currant 
tomato (Ly coper sicura pimpinellif olium) , and horsenettle (Solanum 
carolinense). Beach (1) added to this list prairie groundcherry 
(Phy ' sails lanceolata) , clammy groundcherry (Physalis hetero- 
pliylla), black nightshade (Solanum nigrum), and petunia. The 
writers (9) found that the fungus is not only capable of infecting 
horsenettle (PL I, D to H) but actually infects it as commonly as 
the tomato and also sporulates on it. Eggplant (fig. 5) is also quite 
as susceptible as horsenettle. Potatoes (fig. 6) in our experiments 
were less susceptible than horsenettle or eggplant, but most of our 
experiments were made with Irish Cobbler, which may be more 
resistant than some other varieties. We have also found that the 
leaf -spot fungus infects CypJiomandra betacea (tree-tomato), So- 
lanum floridanum, (PI. II, D to F), Solanum mammosum, and 
Datura stramonium (PL II, A to C). Quite likely it infects a num- 
ber of other hosts. 
Aside from the tomato the only known hosts of this fungus com- 
monly found in the fields of the Middle Atlantic and Middle West- 
ern States are jimsonweed, purple thorn apple, horsenettle, potato, 
black nightshade, prairie groundcherry, clammy groundcherry, 
and eggplant. The tomato, potato, and eggplant crops should be 
thoroughly plowed under at the end of the growing season, and the 
other hosts should be kept out of the fields and waste places, such as 
fence rows and roadsides. 
3 Septoria lycopcrsici grows slowly but fruits abundantly on wheat straw. 
2Q22° 24 2 
