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CoLOKADO Experiment Station 
leaves. Spores from these leaves 
infect young leaves and fruit in 
the spring. These form a new 
crop of spores and spread the 
disease from place to place. 
Scab can be controlled by 
spraying with lime sulfur, one 
gallon of concentrated solution 
(testing 32 degrees Baume) to 
forty gallons of water. To this 
should be added two pounds of 
arsenate of lead to fifty gallons 
of diluted spray. Applications 
should be made as follows: (1) Just before the flower buds open. 
(2) Just after the petals fall. (3) Two weeks after the second spray. 
In dry seasons the latter spray may not be necessary. 
Experiments made in New York state have demonstrated that 
scab may be controlled by the application of a mixture of powdered 
sulfur and arsenate of lead. Applications must be made with a 
special dusting machine from both sides of the trees using one and 
one-half to two and one-half pounds of the mixtures per tree. Make 
at least three applications at the times recommended for the spray 
and in rainy seasons a third or fourth should be applied. 
Black Rot (Physalospora cydonia) (8) — Black rot occurs more or 
less throughout the state. The disease affects the fruit, twigs and 
leaves. The fruit is attacked usually when nearly mature, decaying 
rapidly and becoming brown at first but later turning black. The 
apples remain firm for some time but eventually dry and shrivel 
up. Just beneath the skin little flask shaped fruiting bodies 
(pycnidia) are formed. Many thousands of spores are formed in 
these, which are pushed out through a small opening at the top and 
scattered about by the wind and rain to infect other fruits and 
twigs. 
On the twigs the disease produces first a discoloration of the 
bark. The discolored area spreads gradually until the twig is girdled 
and it often spreads to the larger branches producing a rough 
canker. Large branches may also be attacked directly through 
cracks and wounds. 
Apple scab on fruit 
