APPLE DISEASES 
vicinity of stands of infected cedars and 
native pome fruits. 
The examination of the orchard men- 
tioned by Mr. Zepp in his letter as quoted 
revealed a very interesting situation. Not 
over 100 feet from the nearest pear tree 
stand half a dozen incense cedar trees of 
various ages, from those but a few years 
old to those probably 50 years old or 
more. <A careful examination of these 
trees showed that practically the entire 
foliage was covered with the telial stage. 
The readiness with which the nearby cul- 
tivated pome fruits, as well as the cedars, 
were infected might easily be understood, 
since the heavy wind currents, moving 
up and down the small canyon in which 
the trees are growing, easily carried the 
spores. 
During the course of the _ writer’s 
studies inoculation experiments were 
taken up and it was shown that practical- 
ly all pome fruits could be infected by 
this rust. 
Hosts 
The hosts upon which the fruiting stage 
of this rust have been produced by inocu- 
lation from the incense cedar, are as fol- 
lows: 
Apple, flowering crab, pear, mountain 
ash, native crab apple, quince, Japan 
quince, serviceberry, thorn apple or haw. 
P. J. O'GARA 
Scab 
Venturia pomi 
H. S. JACKSON 
Apple scab is the most serious and most 
generally distributed fungous disease of 
the apple known, and in the Northwest 
during favorable seasons, west of the Cas- 
cade mountains, is particularly severe. 
Symptoms 
Apple scab attacks both foliage and 
fruit. On the foliage the spots are at first 
more or less circular in outline, olive 
green or brown in color, becoming darker 
and more irregular in shape as they be- 
come mature. The leaves are frequently 
more or less curled or wrinkled. When 
the spots are abundant, the leaves fall 
prematurely and considerable defoliation 
may thus take place when infestation is 
487 
abundant. This may result in a failure 
of the fruit buds to develop normally and 
so affect the amount of the crop the fol- 
lowing year. 
On the fruit the fungus produces more 
or less circular spots of a greenish-black 
color. The vegetative stage of the fungus 
causing the disease develops under the 
cuticle of the apple fruit, finally ruptur- 
ing it by the elongation of the threads 
which bear the spores. The ruptured 
cuticle may frequently be seen clinging as 
whitish membranous shreds about the 
edge of recently developed spots. As the 
spots become older, all trace of the fungus 
may become obliterated and the only evi- 
dence of the former spot is seen in a large 
or small, rough, russeted spot. Fre- 
quently the fruit is distorted when mature 
as the result of early scab infections. 
Where scab spots are abundant the fruit 
may become cracked. Scab in any degree 
of severity on the fruit renders it un- 
sightly and unmarketable as fancy fruit. 
In the spring of 1912 at Corvallis, apple 
scab was observed to develop abundantly 
while the trees were in blossom on the 
sepals, petals and ovaries, aS shown in 
Fig. 1. 
Cause 
As noted. above, apple scab is caused by 
a parasitic fungus. The technical name 
of this fungus is Venturia pomi. Two 
distinct phases are known, the conidial or 
summer spore stage and the sexual or 
ascus spore stage. The summer spore 
stage develops on both foliage and fruit 
Ore Lap. Sra. 
Fig. 1. Apple Scab on Blossoms. Note spots 
on petals, sepals and ovaries. 
