462 INSECTS AFFECTING VEGETATION 



The disease is readily controlled by spraying. Thorough prun- 

 ing is important, and if light and air have free access to the fruit the 

 disease usually gives little trouble. 



Apple Scab. The disease appears first on the leaves. Here 

 it may be evident early in June as slightly elevated spots of a lighter 

 green color. At this stage the mycelium of the fungus is largely be- 

 neath the cuticle. It soon breaks through to the surface, giving the 

 leaf a velvety, olivaceous appearance. Spores are produced in abund- 

 ance and probably serve as the chief source of infection for the fruit. 

 As a result of the fungous attack the leaves often become distorted 

 and finally fall early in the season. (N. H. E. S. B. 142.) 



It is on the fruit that the fungus produces its most characteristic 

 and serious effects. Here it forms superficial olive colored spots 

 known among apple dealers as scab, fungus or black spot. The 

 spots are usually % to ^ of an inch in diameter. The mycelium 

 begins its development beneath the cuticle, but soon sends up erect 

 sporophores (spore stalks), which break through to the surface to 

 free their spores. The spores and sporophores give the spot its sooty, 

 olivaceous appearance. The marginal portion of the ruptured cuticle 

 usually remains, giving the spot a light gray border. The fungus 

 checks the growth in the adjacent tissue to such an extent that apples 

 attacked early in the season often become dwarfed and one-sided, 

 and sometimes badly cracked. 



The disease can be controlled by spraying. To be most effective 

 the spraying must be made before the fungus has gained entrance 

 to the host as when it is once beneath the cuticle it may continue to 

 develop in spite of the application of fungicides. In badly affected 

 orchards it is advisable to make a spraying before the leaves are out. 

 At this time copper sulphate, 1 pound to 25 gallons, may be used, 

 or a strong Bordeaux or lime-sulfur solution. The first regular 

 spraying should be made after the leaves have expanded and before 

 the flower buds open. Bordeaux or lime-sulfur may be used for this 

 and for later applications. The second spraying should be given 

 when most of the petals have fallen. This application is the most 

 important of the season. When the disease is at all serious two more 

 sprayings are needed, the third about three weeks after the second 

 and the fourth early in August to prevent a late spread of the disease. 

 (N. Y. E. S. B. 142.) 



Spray Injury. Injury from Bordeaux mixture is of quite 

 common occurrence. On the leaves it appears first as purplish brown 

 spots of various shapes and sizes. They are usually smaller, more 

 irregular in shape and more thickly distributed on the affected foli- 

 age than the leaf spot previously described. Soon after the appear- 

 ance of these spots the leaves may begin to turn yellow. Leaves so 

 affected soon fall, and in serious cases the trees may be almost en- 

 tirely defoliated. Such extreme cases, however, have been very rare. 



On the fruit the injury appears first as small, black or brown 

 specks scattered thickly over the apple. Later in the season the skin 

 may become corky and russeted. In serious cases the apple may be 

 much roughened and deformed, and large, deeply-sunken scars de- 



