Apr. 26, 1924 
Leather Rot of Strawberries 
373 
Average temperature 
°c_ 
1 . 0 
3. 6 
8 . 2 
11 . 8 
12 . 6 
14. 7 
15. 4 
17. 6 
19. 1 
Diameter of growth 
in mm_ 
0 . 0 
0 . 0 
3. 5 
4. 4 
5. 6 
6 . 2 
* 
6 . 9 
7. 5 
8 . 0 
The growth at room temperature, 20 to 25°C. averaged 8.6 for the 10 days. 
At 36°C. there was no growth at all. Evidently, therefore, the optimum for 
growth lies somewhere between 25 and 36° C. though no tests were run at these 
intermediate temperature, since they were not obtainable at the time the above 
test was made. The growth at 8.2°C. was a flat, dense surface mat; at higher 
temperatures the growth was more aerial and fluffy, both of these characters 
becoming more pronounced with each successive rise in temperature. At all 
temperatures where growth occurred the fungus grew both on the surface of and 
down into the agar. 
In holding tests. —As already noted, the fruit used for holding tests was appar¬ 
ently healthy when stored. Yet after four days’ storage at 40 to 45°F. all 14 lots 
of this fruit showed 4 per cent or more of rot (Table VIII) and six of them 25 to 
nearly 70 per cent. The rots found on the first day after removal from storage 
were caused by Phytophthora, Pezizella, Rhizoctonia sp. and Botrytis, with rot 
caused by Phytophthora greatly exceeding the other three in 11‘of the Klondike 
lots and about equaling them in the other Klondike lot and two lots of Aroma. 
At temperatures between 40 and 45°F., all of the fungi named, but especially 
Phytophthora, were able to grow so rapidly that within four days they rendered 
a large part of the fruit worthless. Most of the infection was undoubtedly present 
though not apparent externally when the fruit was stored. The remainder must 
have developed through spread of Phytophthora from diseased to healthy berries. 
Evidence that this had happened was seen repeatedly during the making of 
counts, and later during the inspection of carload lots of strawberries on the 
Chicago market. The problem, however, is one which cannot be solved without 
further investigation. 
CONTROL EXPERIMENTS 
Strawberries used in the holding tests discussed above came from a number of 
fields near Beebe in which experiments had been conducted on control of fruit 
rots by spraying and dusting. The details of these experiments and the apparent 
effect of spraying and dusting on percentage of total rot have been reported (13). 
The data on leather rot are given in Table X, together with data for “other rots” 
and total rot, which are included for purposes of comparison. 
Table X. —Effect of spraying and of dusting on fruit rots of strawberries, at 
Beebe, Ark., 1923 
Holding tests, per cent of rot four days 
after picking 
Spray 
Copper 
dust 
Sulphur 
dust 
Control. 
KLONDIKE-THORNTON PLOTS 
Leather rot _ _ 
22.5 
24.3 
0 
34. 8 
Other rots _ _■_ 
2.1 
1.7 
0 
1.8 
Total rot _ ___ 
24.6 
26.0 
0 
36.6 
KLONDIKE-ABINGTON PLOTS 
Leather Rot . .. _ _ 
16.3 
16.8 
0 
18.0 
Other rots. _ ___ 
2.8 
5.8 
0 
10.3 
Total rot. 
19.1 
22.6 
0 
28.3 
AROMA-THORNTON PLOTS 
Leather rot . __ _ 
17.2 
19.6 
4.5 
17.7 
Other rots _ __ __ __ __ _ 
21.9 
40.4 
37.0 
42. 9 
* Total rot __ .. _ 
39.1 
55.8 
41.6 
60.3 
