302 
240 WM FUNGUS Mats 
(__] TEMPERATURE 
200 
PRECIPITATION 
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OcT. NOV. DEC. JAN, 
Ittinois NaturAL History Survey BULLETIN 
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MAR. 
Vol. 26, Art. 3 
DEVIATIONS FROM 
THE ANNUAL MEAN 
PRECIP | TEMP. 
(INCHES)| ( °F.) 
+47+40 
+37 +30 
+2+-+20 
+1 +10 
2.5+48 
-I+-10 
-27+-20 
(ee eee -3+-30 
APR. MAY JUNE JULY 
Fig. 14.—Monthly mean temperature and total precipitation, both shown as deviations 
from the annual means, and the numbers of mycelial mats of Endoconidiophora fagacearum 
found on wilt-killed oak trees in five Illinois study areas, October, 1952, through ‘July, 1953. 
The bars illustrate the possible influence of monthly temperatures and precipitation on the 
numbers of mycelial mats of Endoconidiophora fagacearum produced on wilt-killed oaks. For 
temperature in October and precipitation in May there were no deviations from the means. 
month on all trees. It can be seen from 
these figures that mat development was 
greatly accelerated during April, May, 
and June. Some of the mats that were 
found in July were small and dry; many 
of them consisted only of pad material. 
They were found by removing bark from 
the trees. None of these undeveloped 
mats bore conidia of Endoconidiophora 
fagacearum. 
Fig. 14 suggests the influences of 
monthly temperature and precipitation on 
mat formation. The average tempera- 
tures for May and June, respectively 16 
and 22 degrees, approached the optimum 
temperature (about 25 degrees) for 
growth of the fungus. The maximum 
temperatures were 32 degrees in May and 
40 degrees in June; each of these oc- 
curred on a day near the end of the re- 
spective month. Although the average 
temperature for July was only 24 degrees, 
a number of days during the month had 
maximum temperatures of 35 degrees. 
Thermometer readings showed that the 
temperature under the bark of wilt-killed 
oaks in unshaded areas was frequently as 
high as 40 degrees. During the winter 
months the highest average temperature 
for any month was 9 degrees, which is too 
low for rapid growth of the fungus. The 
total monthly precipitation for the five 
study areas during the winter months was 
generally below the annual mean, but 
during the spring and summer it was av- 
erage or above. 
The ripe fruit odor associated with En- 
doconidiophora fagacearum was most no- 
ticeable during May, probably because of 
the presence of a large number of mats on 
the trees. Only at this time of the year 
could the odor be detected clearly at a dis- 
tance of 10 feet from the trunks of mat- 
bearing trees. 
Wounds.—The development of mac- 
roscopic mycelial growth of the oak wilt 
fungus was sometimes stimulated by 
wounds made through the bark of trees 
that were in or nearing the mat-producing 
stage. This type of growth, noticeable 
only during March, April, and May in 
the study areas, was first seen late in 
March on tree R-7, which had been felled 
in December. Where small areas of bark 
had been cut from trees with an ax 2 
weeks previously to check on the condition 
of the wood, dense masses of fresh myce- 
lium had developed from the edges of the 
i. 
