I have a very large Norway maple that almost always has leaves infected with anthracnose and sometimes tar spot, depending on the weather during the spring and summer. I have always read that it is important to rake up all the infected leaves and dispose of them in order to minimize re-infection the following year. Mulching and leaving the leaves with the fungus on them seems to contradict this. I would love to avoid the work involved in disposing of the infected leaves, but it seems too good to be true. Please comment.
Although we don’t have any scientific studies of how mulch mowing might affect disease inoculum survival and dispersal, we also don’t have evidence to suggest that it makes these disease issues worse in an urban forest environment (e.g.; a wooded neighborhood) where Norway maples are fairly common and where other factors could be at work to influence over-wintering and subsequent dispersal. With anthracnose in particular, the inoculum source is not likely to be just on the leaves.
One expert suggests that tar spot tends to be very prevalent for a year or two and then has been observed to become much less dramatic, even when no one takes any action at all. Weather fluctuations and other competing pathogens will most likely affect tar spot build up over time, as well.
Thus you have a personal choice: either perform a practice such as LELE mulch mowing that could increase organic matter in your lawn’s soil, and that could in turn benefit both your trees and your turf; OR DO NOT employ this practice on the chance that removing leaves will lessen the occurrence of said commonly occurring diseases (in this case, on an invasive species).
Your observations over time, concerning whatever path you choose, would be interesting to document and share.