THE CONTROL OF TOMATO LEAF-SPOT 17 
Large stocky plants at least 6 weeks old can be produced cheaply 
outdoors in the South and shipped north at any convenient date for 
planting. More than 30,000,000 southern-grown tomato plants were 
shipped into Indiana and a considerable number into Eastern States 
in 1923. Some of the larger northern companies manufacturing 
tomato products grow their own plants in the South. Although the 
use of southern-grown plants in the North has increased rapidly in 
the past seven years, it has distributed wilt and root-knot in many 
clean fields. The need of a system of plant certification is therefore 
apparent. 
The overwintering of the leaf-spot fungus can be largely prevented 
by plowing under the old tomato vines in the autumn. This fungus 
overwinters chiefly on the old vines but can not live until spring in 
the soil. Plowing under the vines in the fall therefore kills it. 
Good results have been obtained by this method in field experiments. 
The vines have to be thoroughly covered, however, to kill all the fun- 
gus on them, but this can be done by cutting them with a disk and 
plowing them under with the aid of a weeclhook or a weedhook and 
jointer. 
The common practice of disking instead of plowing under the 
old tomato vines in the fall is doubtless largely responsible for leaf- 
spot epidemics in the United States. The parts of the old vines left 
lying on the surface of the soil furnish excellent material for the 
overwintering and saprophytic development of the fungus. 
The tomato leaf -spot fungus also grows and produces spores on 
dead weeds, grasses, and the remains of various crops, especially 
cornstalks. Keeping these dead materials covered with soil by plow- 
ing or cultivating robs the fungus of this food supply and increases 
its difficulty of living from year to year as a saprophyte. 
The destruction of horsenettle, groundcherry, jimsonweed, and 
nightshade, on which the leaf-spot fungus lives as a parasite, the 
burning of dead weeds and grasses along fence rows and in other 
waste places, and the practice of clean culture generally will aid in 
the control of this disease. 
