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Clean up Fall Leaves and Clean Up Leaf Spot Diseases

Michelle Grabowski, UMN Extension Educator

M.Grabowski, UMN Extension

Photo 1: Fallen Leaves Infected with Apple Scab

As the weather turns cold, disease management in the yard and garden shifts from thinking about protecting plants this year to working to reduce disease problems next year. Many leaf spot diseases of shade trees overwinter in the fallen leaves below the tree. Apple scab on crab apple and tar spot on maple are two examples. When warm wet spring weather returns, these leaf spotting fungi become active again and produce spores that are then blown or splashed onto new emerging leaves. This starts the disease cycle all over again.

Gardeners can help reduce the amount of leaf spot fungi surviving from one season to the next by raking up and removing leaves from underneath trees that experienced a leaf spot problem this year. Leaves should be properly disposed of in a backyard compost or at a municipal or commercial compost facility. The compost needs to heat up in order to kill the leaf spotting fungi.

Removing leaves will reduce the amount of fungi available to start disease next year. Unfortunately it is not a guarantee that leaf spots will be eliminated. Fungal spores can blow in from neighboring trees and some fungi can infect small twigs in the canopy in addition to leaves. Reducing the amount of fungi directly below the tree can slow the disease down, reduce the number of leaf spots, and possibly even eliminate the problem.
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