12 BULLETIN 1288, U. S. DEPARTMENT OF AGRICULTURE 
obvious. It is doubtful, therefore, whether corn should ever im- 
mediately precede tomatoes in an area heavily infested with leaf-spot. 
USE OF MANURE AND FERTILIZERS 
A liberal use of commercial fertilizers, barnyard manure, or green 
manure is essential on most soils to produce a profitable crop. In 
fact, the best yields of tomatoes in the East and South are usually 
obtained by growers who keep their soil in a fairly high state of 
fertility by the use of liberal quantities of organic matter and 
commercial fertilizers. 
Fertilizers, if properly balanced and judiciously used, do not in- 
duee susceptibility to leaf-spot (11). Plants growing very rapidly, 
however, are more susceptible than those growing slowly. An ex- 
cess of nitrogen or a very heavy application of mixed fertilizer in a 
wet season or on low wet land may cause excessive vine growth, 
especially in late varieties, and this usually induces increased sus- 
ceptibility to leaf-spot. Moreover, heavy vine growth generally re- 
sults in the production of very little pollen and consequently a poor 
set of fruit. Where a poor set is common it would probably be 
advisable to withhold part of the nitrogen until the fruit begins 
to set. More can then be applied with safety, as the growth of 
the fruit checks the growth of the vine. 
The chief use of fertilizer is to produce fruit. A certain growth 
of vine is necessary for high yields, but an excess retards fruiting 
and not infrequently reduces the yield. Fruiting should start early 
and continue during the season normal for the variety, as the 
quantity of fruit a vine can produce at one time is limited. The 
moderate proportion of foliage usually accompanying high yields 
of fruit dries off quickly after rains and therefore offers less op- 
portunity than heavy dense vines for the development of leaf -spot. 
SPRAYING AND DUSTING 
Tomato leaf-spot can be controlled to a considerable extent by 
repeatedly spraying 4 (fig. 7) or dusting the plants with fungicides. 
Of these two processes, spraying has usually given the better results. 
The increase that can be obtained from spraying tomatoes differs 
somewhat, however, because of differences in the fertility of the soil 
and variations in the severity and duration of the disease. On a soil 
capable of producing high yields spraying is commonly profitable 
if the disease is severe, but on poor land it often gives little, if any, 
increase over the expense. In the latter case it would be more 
profitable to spend the money for extra fertilizer. Moreover, if 
the disease is only of moderate severity or if its development is 
delaj^ed until the crop is nearly mature, it may not do enough dam- 
age to make spraying profitable. Profits from spraying are also 
affected by prices of tomato fruit. An increased yield may be profit- 
able when the price of the fruit is high and unprofitable when it 
is low. 
* Either 4-4-50 Bordeaux mixture ii pounds copper-sulphate crystals, I pounds stone 
lime, and 50 gallons water) or 4-2-50 Bordeaux mixture (4 pounds copper-sulphate crys- 
tals. 2 pounds stone lime, and 50 gallons water) usually gives fairly good control of the 
disease if thoroughly applied at proper Intervals. The effectiveness of these spray mix- 
tures is improved, however, by the addition of 2 or '■'> pounds of rosin-tishoil soap to each 
50 gallons. Before the soap is added it should he dissolved in a small quantity of hot 
water. 
