The garden is getting ready for winter. Unfortunately, so are many of the pathogens that cause plant disease. These stinkers are fungi, bacteria, virus and nematodes. Bacteria, viruses and some fungi will spend the winter happily cuddled up in live tissue like perennial stems or inside dormant leaf buds where we can’t get at them. Unlike the Martha types who cut everything down to the soil line, we like to leave perennial stems uncut for some types of bees to use for their winter home. Some plants hold their seeds all winter making for a grocery stop for our hungry winter birds. Then there are the fungi. They will survive in a dormant state on plant debris or in the soil as reproductive spores or dormant mycelium. This type can live through a cold spell of several months without a host plant. One type of fungi form sclerotia, a hard structure that can survive a wide range of temperatures and even years without a host plant to infect. There isn’t much you can do to kill this one now. For much of the rest, we can at least reduce the amount of pathogens in the gardens by a good clean up of diseased plant material.
If you leave your tomato vines in the garden you may be harboring a white mold. It can live for years in the soil and on plant debris. Powdery mildew on your phlox can live through the winter and release spores in the spring to re-infect the plant. Another bad guy is tar spot on Maple trees. These spots are fungal stomata, fruiting bodies that will open in the spring to release spores.
Plant pathogens can survive quite nicely on plant tissue that they have already infected. As the leaves and stems die back for the year, the fungi that caused spots, rots and other problems either go dormant or, even worse, remain active feeding on plant debris. Then as the weather warms up in the spring, the fungi become active again and infect next year’s stems and leaves. There is a solution. Cut any diseased plant to the soil line and bag the material. Infected tree leaves get the same treatment. Don’t leave infected material near the garden as the pathogen can easily move back in for the winter through rain, wind, or even your feet.
Many pathogens can survive the winter on garden stakes or trellises. Clean these with a 10% bleach solution before you put them away for the winter. You may forget next spring. Don’t use bleach on your tools as it is very corrosive. Instead, use Lysol or mouthwash with alcohol in it. Clean and sharpen your tools as you clean them so you are ready for next spring.
To cut down on winter-kill of perennials, mulch your flower gardens with a nice thick blanket of disease-free leaves. If you chop them up, they will behave themselves and stay in place all winter. Leave this blanket on all year. This will prevent weeds, keep the roots cool and hold moisture all summer. It may even keep soil-borne fungi from getting to your plants. A layer of leaves tilled into the vegetable garden will slowly rot during the winter adding micronutrients to the soil and loosening heavy soil. A much better use for them than burning them and adding to air pollution. You gotta breath that air.
Seems like there is no end to fall chores. A snowstorm will do that nicely. Then we can spend the winter thinking and planning how to make next years’ gardens better.
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.