396 AGRICUI.TURE OF MAINE. 



or more frequently especially if viewed with a magnifying glass 

 of low power it will be seen to be ramifying and much branched 

 giving a beautiful, delicate, "moss agate" effect. Badly attacked 

 leaves may be more or less curled and crinkled and where defoli- 

 ation occurs a pronounced yellowing may appear. Fig. 66 

 shows the characteristic appearance of a well developed leaf 

 attack where the spots have run together along the veins. 



Scab on apple leaves was very abundant in Alaine during the 

 summer of 1910 and samples showing the disease were received 

 by the Experiment Station repeatedly from all of the apple grow- 

 ing sections of the State. Cool, moist weather either in the 

 spring or summer favors the development and distribution of 

 scab, while hot, dry winds and sunny days tend to keep it in 

 check. 



Two forms of spores are produced on apple leaves. If some 

 of the olive-colored growth from the living leaves where the 

 fungus is growing parasitically is scraped off and examined 

 under the microscope a large number of the summer stage spores 

 are found. These, and like spores produced on the fruit spots, 

 are responsible for the summer spread of the disease. In the 

 winter the fungus develops saprophytically in the fallen leaves 

 under the trees and there produces an entirely different type of 

 spore. While the summer spores can live for some time and 

 doubtless it is not impossible for them to remain alive over win- 

 ter especially on fruit left on the trees or on the ground it is 

 probable that much of the spring infection comes from the win- 

 ter spores formed on the fallen leaves. It is a matter of common 

 experience that the lower leaves on the tree are the first to show 

 attacks of scab in the spring. Hence raking and burning the 

 leaves would do much to lessen the danger of infection. The 

 formation of winter spores takes place more readily when the 

 leaves fall on sod or are partly covered by grass, other leaves, 

 etc. Orchard cultivation produces conditions unfavorable to 

 the propagation of scab spores and early spring plowing buries 

 many of them where they will decay and do no damage. 



Scab on the fruit is too familiar to need much description. It 

 first appears as small, circular, olive-colored spots on the skin 

 of the apple, these later enlarge, many of them becoming one- 

 fourth of an inch or more in diameter, roundish, roughish and 

 dark olive-colored, usually surrounded by a light gray border. 



