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Fall Residue Control and Disease Prevention

The cool summer and ample moisture of this season have led to many complaints of fungal pathogens in southern Minnesota. Some of the most damaging and common ailments that devastate vegetables and fruits—anthracnose, early blight, and verticillium wilt—can overwinter on dead plant stems and leafs. If one simply leaves the residue on the surface, these pests can continue to pose a risk to your garden.

As with many diseases, prevention is preferable and more effective. For fungal pathogens specifically, disposal of infected material is key. The oldest and dirtiest method, burning residue, can be effective but must follow ALL local and county laws. Instead of burning, many cities have lawn waste drop off that can work just as well in removing overwintering spores from your property.

A simple and more labor-intensive method, tillage, is another “old” technique to control the amount of disease in the field. Certain fungi such as anthracnose tend to die once covered with three inches of soil. A word of caution, other fungi thrive if buried, particularly verticillium. Be certain which diseases your garden has had before committing to an intensive tillage regime.

Composting diseased plant material to kill pathogens is possible but comes with considerable risk. Temperatures can be 122˚F inside the pile, but if not properly maintained, heat radiating from the middle may not kill infected material on the outside. When you apply this partially treated compost in the spring, spores may re-infect the same beds they had before.

Certain apple tree fungal diseases, such as apple scab, can be tackled with a unique approach. By mowing fallen leafs of an infected tree then applying a 5% nitrogen/water solution, earthworms and bacteria quickly attack. This feeding frenzy decomposes the leaf material quicker than normal, and disrupts the life cycle of the fungus. This mowing/fertilizing technique works best when temperatures are not freezing, as it requires living organisms to help. Therefore, it may not be applicable late in the season with a frozen soil.

Another way to disrupt the life cycle of the fungus is to adhere to a strict rotational system in your garden. By not planting a species from the same botanical family in the same spot for four or more years, these fungal diseases can die after being dormant too long. One common rotational scheme used by many growers is as follows:

Year 1: Solanaceae (eggplant, tomato, potato, or pepper)
Year 2: Brassicaceae (cauliflower, broccoli, kale, or kohlrabi)
Year 3: Cucurbitaceae (melons, squash, cucumber)
Year 4: Apiaceae (carrot, parsnip, dill, parsley)   

Again, this rotation is not the end-all-be-all of rotations. Other popular species that do not belong in the listed families include beans (Fabaceae), garlic (Liliaceae), and corn (Poaceae). Feel free to tweak the rotation according to your needs. Also, aim to select vegetable varieties that are resistant to many fungal diseases.

This season has had its share of challenges. However, by practicing good fungal hygiene in the yard and garden, you can give yourself as clean a slate as possible for the next growing season.


Shane Bugeja
Extension Educator, Ag Production Systems
(507) 304-4325
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