Feb. io, 1923 
A Bacterial Leaf spot of Tobacco 
491 
TabIvE I .—Percentage of “rust” on fertilizer test plots 
Plot 
No. 
Fertilizer applied per acre. 
Yield in 
pounds of 
cured leaf 
per acre. 
Percentage 
of plants 
rusted. 
3. 
Barnyard manure, 20 tons... 
1,545 
1,242 
43 
46 
8. 
.do. 
1. 
Average. 
1,393 
44* 5 
No fertilizer. 
1, 682 
i,527 
23 
26 
7. 
.....do. 
2 . 
6 . 
Average. 
1, 604 
24- 5 
200 pounds nitrate of soda, 200 pounds sulphate of pot¬ 
ash, 600 pounds acid phosphate. 
.do.. 
1.69s 
735 
11 
10 
Average. 
I # 7I5 
10.5 
It does not follow from this, however, that “rust” is more likely to 
occur in low-yielding crops, the manured plots in this test being in fact 
an average crop. The condition is rather one of “physiological or nutri¬ 
tional balance” in the plant, a condition, as yet very inadequately under¬ 
stood in relation to plant diseases. A practical suggestion for experi¬ 
mental work in reducing damage from this disease by proper fertilization 
is offered, however, by such observations. 
It has usually been found that the first or primary infection starts in 
the seed bed and that the secondary infection in the field is a direct 
result of transplanting infected plants. The same seems to be especially 
true of the wildfire disease. In the springs of 1917 and 1918 infection 
with Wisconsin leafspot was first noted in the seed beds at the Wisconsin 
Agricultural Experiment Station, and subsequently secondary infection in 
the field was found in areas in the field planted from the infected areas in the 
seed beds, although a considerable time intervened between the two appear¬ 
ances of the disease, during which time it had apparently disappeared. 
This experience, together with a similar, and now common, experience 
with the wildfire disease, offers the suggestion that seedling plants from 
areas showing signs of infection should preferably not be transplanted 
into the field. It is not improbable that spraying with copper sprays 
in the seed beds as suggested for wildfire (5) may also help to control 
the Wisconsin bacterial leafspot should conditions warrant its use. 
The manner in which the disease lives over winter is not definitely 
known. The causal organism may pqrhaps live over on the seed, on 
the cloth covers, possibly in the soil, or by other means. Until this is 
determined no satisfactory means of control from this standpoint can 
be offered. 
Although a considerable number of varieties of tobacco have been 
grown at the Wisconsin station annually, these have not all been equally 
exposed to infection. From limited observations and experiments* 
however, the writer feels safe in concluding that differences in varietal 
susceptibility or resistance are small, if in fact they exist at all. 
25622—23-8 
