Apr. 26, 1924 
Leather Rot of Strawberries 
371 
to obscure the rise and fall in amount of rot due to any one of them. Under 
such conditions it % might easily have seemed, as it actually has to growers many 
times, that rot on any given day had resulted from the weather of that or the 
preceding day. When the course of one attack, as in the instance under dis¬ 
cussion, can be followed from beginning to end, the lag in occurrence of the 
maximum as well as the duration of the attack both become very apparent. 
Under this topic one more point remains to be covered. As mentioned earlier, 
growers have observed that leather rot often occurs when rainfall is not heavy 
but merely more or less continuous for several days. It is therefore worth noting 
that the rot did occur in just such weather during the course of the work here 
described. The four days from May 2 to May 5 were rainy, but the heaviest 
rainfall on any one day was less than 0.2 inch. There was also a rain of 
0.06 inch on the 8th. Yet during the five days from May 5 to 9, the first counts 
being made on the 5th, leather rot was found as follows: 
In the field 
In holding 
tests 
May 5 
6 
7 
8 
9 
No counts. ...... 
1.3. 
No counts. 
0 .0. 
3.1. 
3.0. 
.do.. ......... 
.do___________ 
8.0 ..... 
5.0......... 
RELATION OF LEATHER ROT TO FIELD TEMPERATURES AND 
DEGREE OF CLOUDINESS 
The relation of leather rot to other elements of the weather besides rainfall 
can not be so easily determined. Laboratory findings and field observations 
justify certain assumptions but are not yet complete or extensive enough to be 
used as a basis for conclusions. For the period from May 14 to 21 general 
cloudiness and fairly low temperatures during the first part of the period pro¬ 
longed the time during which both soil and plants were covered with a film of 
moisture. This, in turn, by favoring the release and distribution of zoospores, 
would presumably increase the amount of rot and lengthen the time during which 
the rot would be heavy. But on the other han,d, higher temperatures during 
the latter part of the period would hasten development of the rot in infected 
berries and so bring the attack to an end sooner, provided there was no further 
rainfall. They might thus account, in part at least, for the sharp drop from 68.5 
per cent of rot on the 18th to 10.9 per cent on the 19th. It is a fact, noted 
both by the writer and by many growers, that during hot weather three or four 
days after a rain leather rot develops and becomes visible very rapidly. On 
the 18th and again on the 26th, 28th, and 29th, all of which had maximum tem¬ 
peratures of 77 to 85° F., numerous packed crates were seen in which the berries 
picked in the morning as being apparently sound had by afternoon developed 
so much visible Phytophthora rot that they had to be thrown away. 
PROPORTION OF LEATHER ROT TO OTHER ROTS 
In holding tests. —During the six-day period mentioned above, the percent¬ 
age of rots other than leather rot (mostly Pezizella and Rhizoctonia sp.) in cold 
storage lots of Klondike berries, showed no progressive increase from day to day. 
In fact, on the 18th when leather rot was the highest, no other rots were found. 
During the period from May 5 to 14 there was no progressive increase in any of 
the rots, probably because rainfall was light and percentage of all rots low. On 
the other hand, there is evidence, furnished, it is true, by only two holding tests 
94527—24t-6 
