We really need a chemical control to slow the spread of blight during summer. Fruit russetting caused by delayed-dormant copper sprays is again evident in some blocks of apples and pears. Copper sprays have been recommended and were applied to reduce fire blight inoculum. However, this year we had only about 2.5 inches of rain between green-tip on 3 April and kingbloom on 4 May. With so little rainfall, copper residues persisted on the tree and were washed to the developing fruitlets beneath the open blossoms.
Copper residues that persist until bloom can cause fruit russetting.
When rainfall between green tip and bloom exceeds 3 or 4 inches as it usually does, we do not see damage from early copper applications. However, the possibility that copper can damage fruit in years with sub-normal prebloom rainfall leaves growers in the unfortunate position of having to decide each year whether they prefer to risk copper damage to their fruit or whether they prefer to take their chances with fire blight. Flyspeck started appearing on unsprayed fruit at the Hudson Valley Lab during the last week in July. Dry weather during June and early July slowed symptom development, but disease development was promoted by eight inches of rain and 138 hours of rain-associated wetting between 23 July and 6 August. Commercial orchards were probably well protected from primary infections by mancozeb used in scab control programs.