A Bulletin on Orchard Practice 17 



unfurl in spring and later these spores escape from the capsule 

 and float about in the air. Some of them lodge on the leaves, 

 flowers and fruit. If they germinate they will cause the parts 

 to become diseased. The summer stage then makes its appear- 

 ance in a few days in the shape of small, usually nearly cir- 

 cular, dark, 'olive green colored blotches. These blotches are 

 composed of numerous short stalks on the tips of which sum- 

 mer spores are borne. The summer spores mature at once 

 and drop off. If they lodge on the leaves and fruit of the same 

 tree or a neighboring one thjey will cause new areas to become 

 diseased. Very shortly a second crop of summer spores is 

 produced by the fungus in the new areas which in turn drop 

 off. Some of them are carried by the wind and other agents 

 to the leaves and fruit and thus spread the disease more 

 widely. Summer spores mature in such a short time and are 

 produced in such abundance that thousands of scabby spots 

 appear in the course of a few days when conditions are fav- 

 orable. As the parts mature the new blotches become less 

 frequent and finally cease to appear. The greater number of 

 them appear during the interval of time between the unfolding 

 of the leaves and a few days after the petals have fallen. The 

 reason that the fungus no 'longer produces new diseased areas 

 is perhaps due to the epidermis (skin) of the leaves becoming 

 somewhat thicker and firmer and thus more resistant so that 

 the fungus is unable to make an entrance. 



Since the fungus that causes the disease winters in the 

 dead leaves it is evident that the destruction of as many of 

 the fallen leaves as possible will materially lessen the number 

 of winter spores to be set free in the spring. Plowing the leaves 

 under in the autumn is perhaps the easiest method of getting 

 rid of a greater number of them. This will not altogether 

 prevent the disease. The trees must be sprayed every year. 



Several sprays have been used in combatting apple scab 

 but none has given as good results as properly prepared Bor- 

 deaux mixture. Two applications applied on the proper dates 

 are sufficient to hold the disease in check. The first application 

 must be made just before the flower buds open and the second 

 just after the petals have fallen. 



