Feb. 7,1916 
Further Studies on Peanut Leaf spot 
897 
were found to have adhering conidia. The usual number found was 
three or four on each plate. The occurrence of rain and heavy dews 
will in part account for the relatively small number of plates upon which 
conidia were found. Rain fell on 9 of the 16 days during which these 
tests were made. The plates washed off by these rains numbered 26. 
Three sets of exposures of three plates each remained free from conidia 
in the periods immediately following rain. In many cases one plate only 
of each set gave positive evidence in the period following. Only six out 
of the 42 plates exposed at night yielded any positive results, owing 
principally to the occurrence of dews. 
At no time during the period in which these tests were made, as will 
be seen, was there a maximum period of spore dispersal. Conidia were 
present in the air, except where it had been rendered free from them by 
precipitation, during the entire period. This is in accord with the in¬ 
crease in amount of leafspot shown in the successive counts made in 
field 10 and recorded in Table II. There was approximately twice as 
much leafspot in field 10 on August 14 as on August 6, and twice as 
much on August 21 as on August 14. No correlation between these 
increases and the temperature and humidity records could be discov¬ 
ered, and these figures have consequently been omitted from Table III. 
The idea formerly entertained 1 that the occurrence of peanut leafspot is 
correlated with certain moisture and temperature conditions is now 
regarded as without foundation. Such a correlation would be meaning¬ 
less in view of the positive evidence, next to be reported, that insects act 
as carriers of leafspot. Details of the tests conducted at Auburn, Ala., 
are not tabulated, since the work accords with the work done at Eutaw, 
Ala., and substantiates the significant fact that air currents are agents 
in the dissemination of Cercospora personata . 
INSECTS AS AGENTS IN DISSEMINATION OF THE LEAFSPOT ORGANISM 
The fact that the leafspot fungus is air-borne explains in part at least 
the failure to secure perfect control in the tests in which rotation and 
seed treatment were combined. No tests have been made, however, 
upon the distance which the conidia may be transported by the wind. 
The most distant exposures were only 8 feet from the nearest diseased 
plant. It seems unlikely that air dispersal could account for severe 
infection in fields in which both rotation and seed treatment had been 
practiced and which were from yi to % mile distant from the 
nearest infected field. It was therefore suspected that certain insects, 
among which grasshoppers are the most important, are agents in this 
spread of leafspot. 
1 “Apparently infection with Cercospora is in some manner correlated with certain moisture and tem¬ 
perature conditions. . . The ravages of Cercospora personata seem to attain their ma ximum severity 
after a dry period followed by excessively sultry weather. . .” (Wolf, F. A. Teafspot and some fruit 
rots of peanut. Ala. Agr. Exp. Sta. Bui. 180, p. 133. 1914.) 
