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Reapply the mulch every few years as it breaks down . The fungus may also infect stub ends of stems from which flowers have been cut . The fungus produces a large amount of cottony white , thread-like material called mycelium , which can grow up the stems of plants and also spread out across the soil to infect other plants . Ideally , the tree should receive one inch of water from rainfall and / or irrigation every week from May through August . For now , however , sanitation ( promptly removing and destroying fallen fruit and leaves ) , cultural practices designed to promote optimum tree health , and perhaps occasional physical or chemical intervention are all that is normally needed to obtain a satisfying crop in most years . The quality of the fruit from these disease-resistant trees is acceptable , although it may not measure up to that of some other varieties recommended in Table 1 for zones 4a and 4b . Mildew diseases of other plants do not infect roses . Control efforts with fungicides require reapplication every 7 to 14 days . Pruning the trunk back in this way is intended to induce branching that will result in scaffold branch options the following year . Excessive pruning should be avoided because it greatly reduces the crop for that year . At that point , caterpillars have grown to about 1 to 2 inches in length . Since this fungus is able to infect many different garden plants , it is important to verify a plant 's immunity . In order to be effective , they must be applied at the first sign of disease and repeated every 7-10 days . Frozen apples release more juice than fresh ones , and you must compensate for the extra liquid . Fertilize the soil every month during late spring and summer , but mix your fertilizer half-strength . Varieties and Rootstocks : Apples Selecting Apple and Pear Varieties Apple flowers must receive pollen from another variety of apple to produce fruit .