LEATHER ROT OF STRAWBERRIES 1 
By Dean H. Rose 
Pathologist , Fruit-Disease Investigations , Bureau of Plant Industry , United States 
Department of Agriculture 
One of the most destructive diseases of strawberries (Fragaria sp.) in the 
southern Mississippi Valley is a rot of the fruit caused by a fungus which seems 
to be identical with Phytophthora cactorum (Leb. et Cohn) Schroeter. Yet until 
the spring of 1922 this rot was apparently unknown to plant pathologists, a 
fact which may perhaps be taken as emphasizing the relatively slight amount of 
attention which has been given to diseases of this important fruit. Even to 
strawberry growers the disease was known merely as “water-soak,” since they 
had observed that it was always most serious during wet weather. On the 
basis of facts to be presented later in the paper, it is proposed that this disease 
be known by the common name of “leather rot.” 
The writer first learned of the disease during the course of a trip through 
the strawberry producing sections of north-central Arkansas and western Ten¬ 
nessee in late April and early May, 1922. The rainfall during that time was 
unusually heavy and had been so for some time previous. The rot was found 
in every field inspected, the loss ranging from 10 per cent in some fields to 25 
and even 50 per cent in others. Losses fully as heavy were noted the following 
year (1923) in the district around Beebe, Arkansas, and a few fields were seen 
in which for several days the loss amounted to three-fourths of the berries then 
ripening on the plants. The average loss for the whole season (1923) in this 
district was certainly not less than 20 per cent of the crop. In sections where it 
occurs, Phytophthora rot is one of the most serious diseases with which the 
strawberry grower has to contend and therefore deserves thorough investigation. 
EARLY FIELD OBSERVATIONS AND DESCRIPTION OF THE 
DISEASE 
In all fields examined berries were found which were somewhat softened but 
tough and leathery and slightly browned—all of these being symptoms well 
known to the growers as typical of “water soak.” After further investigation 
it seemed certain that they were caused by the attack of a parasite. Some 
fruits were seen which showed a white mold on the surface while still attached 
to the plant; others developed the mold after being held over night in a moist 
chamber. Mounts^ from the superficial growth showed almost always large 
numbers of conidia that were strongly suggestive of Phytophthora and cultures 
from affected fruits, whether moldy or not, yielded a white fungus; the fungus 
was later shown to be similar to and probably identical with Phytophthora cac¬ 
torum, and its pathogenicity proved by inoculations. 
In the field, Phytophthora rot (leather rot) affects strawberry fruits at all 
stages, from blossoming to full maturity. On all of them it is characterized by 
a definite though rather slight softening of affected tissues, by both external 
and internal discoloration and usually by a marked bitter taste; the tissues, 
however, become tough and leathery, so that the softening never even approxi¬ 
mates the mushy, leaky condition produced by Rhizopus sp. nor the “soft rot” 
condition produced by Pezizella lythri (11). 2 The discoloration, particularly on 
the outside, varies so greatly that it must be described in detail. 
1 Received for publication Feb. 9,1924. 
* Reference is made by number (italic) to “Literature cited,” p. 374-375. 
Journal of Agricultural Research, 
Washington, D. C. 
( 357 ) 
Vol. XXVIII, No. 4 
Apr. 26, 1924 
Key No. G-394 
