For growers that have had trouble with apple scab there are two things that you can do now to prevent disease pressure next spring: mowing and spraying urea on the ground on the falling leaves.
Two fact sheets outline the details and are worth review:
Reducing Apple Scab Risks and Saving Scab Sprays (UMass)
Reduction of overwintering inoculum in orchards with apple scab (MSU)
Dan Cooley, UMass notes,
“In a commercial orchard, virtually all of the spores that can start an apple scab epidemic come from within the orchard. Scab spores don’t travel very far, generally no more than 100 ft. Add to this the fact that early in the season, from green tip to tight cluster, only a very small proportion of the scab inoculum matures and is available to cause infection. This means the risk of scab infection early in the season can be greatly decreased by reducing or eliminating any old infections in apple leaves on the orchard floor.
Research in New England has shown that either flail chopping or urea applications will reduce apple scab inoculum. In addition, in very low inoculum orchards, it is possible to delay the first scab fungicide applications as late as pink, or until after three infection periods have occurred (whichever comes first). In this fact sheet, we present methods describing how to do both things: reduce the amount of scab inoculum in an apple block; and measure the inoculum in a block in order to decide whether the first scab fungicide may be delayed.”From the UMass fact sheet:
Regardless of the scab management program used in an orchard, we recommend reducing apple leaf litter and the scab inoculum it contains. It is a relatively inexpensive and reliable method that decreases the risk of apple scab.
Shredding all leaves on the orchard floor in November or April reduces the number of scab spores by about 85%. If the strip under trees cannot be reached with shredding equipment, then flail chopping the remaining area between trees will reduce scab spores by about 50%. Small leaf pieces break down quicker, and are more readily consumed by earthworms. If shredding is done in April, it will flip leaves and leaf pieces over. The scab fungus has already started to grow by the spring, and forms fruiting structures that will release spores up and into the air. Flail chopping flips probably about half the leaves or pieces over, and spores formed in those pieces of leaves cannot release into the air.