892 
Journal of Agricultural Research 
Vol. V, No. 19 
total number of plants on a certain area was first counted, and then a 
count was made of those plants which were diseased. A plant having 
only a single spot on one of its leaves was regarded as diseased. Several 
attempts were made to determine the decrease in yield due to leafspot, 
but no satisfactory method has been found and the figures given are only 
approximate, since they were obtained by determining the average differ¬ 
ence in the number of peas borne on 10 healthy and 10 diseased bunches 
having apparently the same-sized tops. It will be noted that the per¬ 
centage of diseased plants in fields designated as 1 to 7, which are repre¬ 
sentative of rotations, varies from 13.5 to 100 per cent. When the results 
for the fields numbered 4 and 8 are contrasted, the former having borne 
no peanuts previously for 11 years and the latter having grown four 
successive crops, with 95 and 100 per cent, respectively, of the plants 
diseased, with practically no difference in the severity of attack, one is 
forced to conclude that rotation in itself is not to be regarded as a control 
measure against peanut leafspot. These results came somewhat as a sur¬ 
prise to the writer. Several reasons for the inefficacy of rotation as a 
means of leafspot control will be brought out later in this report. It 
might be suggested at this point, however, that this much overworked 
and overrecommended suggestion for the control of plant maladies is not 
a panacea, but requires experimental proof for each particular trouble 
for which it is recommended. 
Table I .—Summary of rotation tests with peanuts made in Alabama in ig $5 
Field 
No. 
Location. 
Previous crops on soil. 
Date of 
examina¬ 
tion. 
Plants 
affected. 
Decrease 
in yield 
of peas. 
Per cent. 
Per cent. 
1 
Auburn... 
Peanuts had been grown 2 years before. 
Sept. 6 
100 
(a) 
2 
Eutaw.... 
Peanuts had not been grown for several years pre¬ 
viously. 
Aug. 28 
54 
5 
3 
.. .do. 
Peanuts had not been grown for 4 or $ years pre¬ 
viously. 
30 
41 
4-5 
4 
.. .do. 
No peanuts had been planted for at least 11 years.... 
31 
95 
, 19 -5 
5 
.. .do. 
No peanuts had been planted the previous year; no 
previous record available. 
Sept. 1 
26 
(0) 
6 
Ho 
No peanuts in field the previous year. 
1 
100 
(a) 
7 
8 
rio, B11 
No peanuts in field for 4 years previously... 
1 
13-5 
100 
( b ) 
.. .do. 
Peanuts had been grown during each of the 4 pre¬ 
ceding years. 
Aug. 27 
20 
a Not estimated. b Negligible, 
SEED DISINFECTION FOR LEAFSPOT CONTROL 
Seed treatment for the control of leafspot was recommended in a 
previous report 1 for two reasons. It had been found that conidia adhere 
to the surface of the shells, and it had been noted repeatedly that the 
disease occurs in fields not previously planted to peanuts. It was sug¬ 
gested that solutions of copper sulphate or formaldehyde be used in dis- 
i Wolf, F. A. Op. cit., p. 134. “ The prevalence of leaf spot in lands not previously cultivated is not 
uncommon . . . conidia and conidiophores have been found in the centrifuged washings of peas.” 
