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Fall cleanup: Key to reducing risk for next year's plant diseases

Cool weather is a reminder that fall is not far away and soon gardeners will be preparing the landscape for winter. Many plant pathogens are able to survive winter in gardens in infected leaves, flowers, branches, and fruit. Gardeners can reduce the risk of plant disease next year by using the following steps to do a thorough fall garden clean up.
green maple leaves with black spots
Tar spot on maple
M.Grabowski, UMN Extension

Trees and shrubs

  • Examine leaves before they change color for evidence of a leaf spot disease. Leaf spots come in many colors, are randomly scattered across the leaf surface, and often are more severe on the lower and inner leaves. They will be easiest to identify when the leaves are green.
  • If a leaf spot disease is found, leaves should be raked up and removed or mulched into the lawn with a mulching lawn mower after normal leaf fall. 
  • Look for branches with wilting or dead leaves. Discolored, cracked or blistered bark on these branches could indicate the presence of a canker infection on the branch. A large tumor like growth on the branch would indicate a gall.
  • If galls or cankers are found, mark the branch with paint or flagging tape to indicate the presence of a problem. 
  • Do not prune to remove the canker or gall until winter however. Trees pruned in fall before going dormant may produce young sprouts that will not have time to harden off before winter and will be killed by the cold temperatures. The best time to prune out cankers and galls is in January or February when temperatures have been consistently below 32℉.

pink flowering sedum plant with brown spots on leaves
Septoria leaf spot on sedum
M.Grabowski, UMN Extension

Flower gardens

  • Examine both annual and perennial flowering plants for spots, rot, or wilt.
  • Mark the plants that are showing symptoms of disease now.
  • After a hard frost kills the plants completely remove diseased annuals and any perennials suffering from a root or crown rot.
  • Perennials with a leaf spot disease can be cut off at the soil level. Infected leaves, stems, and flowers should be removed from the garden.
  • It is ok to leave plants that have no symptoms of disease for winter interest or to support wildlife.

Green bean leaves with brown spots with a yellow halo
A bacterial leaf spot disease of green bean
M.Grabowski, UMN Extension 

Vegetable gardens

  • In a small vegetable garden it is best to remove all plants that had symptoms of a plant disease during the growing season and place them in a compost pile.
  • For large gardens, infected plants can be cut down and buried in the garden soil. In this case, the gardener should use crop rotation, and avoid planting any plant from the same plant family as the diseased crop on the site for the next 3 to 4 years.
  • Leaves from deciduous trees can be placed on the soil of a vegetable garden to prevent soil erosion over winter and provide shelter to native pollinators. 

black compost bin next to a pink flowering bleeding heart
Backyard compost bin
J. Weisenhorn, UMN Extension

What to do with diseased plant material?

  • Do NOT put any landscape plant material into the garbage. 
  • Diseased plant material should be composted in a compost pile that heats up to 148℉ and results in complete breakdown of all plant material. This will kill the majority of plant pathogens commonly found in Minnesota landscapes. 
  • If your backyard compost pile does not heat up sufficiently plant waste can be brought to a municipal compost facility. Some cities offer curbside pickup of compostable items.

bright red male cardinal sitting on a branch
Northern cardinal
S. Katovich, USDA Forest Service 

Pollinators and Wildlife

Many birds, native pollinators, and other wildlife utilize the plants in our landscapes to help survive the winter. While it is important to remove diseased plant material from the yard and garden to reduce the survival of plant pathogens, it is also important to leave healthy flower stalks, seed heads, grasses, fallen leaves, and other plant parts in the garden to support Minnesota’s pollinators and wildlife. 

M. Grabowski, UMN Extension Educator 

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