With autumn in the air, gardeners’ thoughts are turning to end of growing season clean-up, and that usually means lots of material going onto the compost pile. But what about diseased plant material that can be very prevalent in the landscape late in the season?
Brian Hudelson, Department of Plant Pathology at the University of Wisconsin, Madison Extension, warns about plant diseases that should not end up in your compost pile.
Not surprisingly, Late Blight makes the list. This disease impacts potatoes and tomatoes and is encouraged by cool, wet weather – something we have not seen much of this year. Hudelson says if you do end up with Late Blight – which affects both the plants and fruit – remove the plants and plant parts, fruits, and any volunteer plants and destroy them. He recommends burning where allowed or double-bagging and sending to the landfill. For next year, use fresh potatoes as seed, which are certified seed potatoes, and grow resistant tomato varieties. Apply fungicides to prevent infections according to label directions BEFORE there are signs of Late Blight.
Impatiens Downy Mildew is another no-no for composting, Hudelson says. Garden impatiens, Balsam impatiens, Jewelweed (native impatiens), and even New Guinea impatiens can act as a host, although New Guinea impatiens have resistance/tolerance for the disease. This disease also likes wet weather.
To control it, do not grow impatiens in the same location every year. Look for tolerant/resistant/immune plants. Do not overcrowd plants, and do not water from overhead. Bag and discard affected plants, including asymptomatic surrounding plants. Fungicide can be used to help prevent this disease.
Verticillium Wilt is another disease that Hudelson says to be cautious about adding to your compost pile. Many woody ornamentals, vegetables, and herbaceous plants host this disease, including maple, ash, redbud, smokebush, tomato, potato, pepper, eggplant, cucurbits, purple coneflower, and blazing star. Cool, wet weather is favorable for infection, while hot, dry weather is favorable for symptom development. It is recommended that you avoid municipal mulches to help control this disease, as well as keep broad-leaf weeds under control and clean up leaf litter. Prune diseased (wilted) areas and burn where allowed. Do not use fungicides for Verticillium Wilt.
Interestingly, Hudelson notes hot compost – with a question mark – as a way to destroy infected plant material in the case of Verticillium Wilt. He does not provide any additional explanation.
I found an article written a few years back entitled “Dos and Don’ts of Composting,” by Steve Reiners, a professor in the Horticulture Section of the School of Integrative Plant Science, Cornell University, Cornell Agritech. Reiners notes plant diseases can survive the compost process, but also says that if he excluded all diseased material, he wouldn’t have much to put in his compost pile. He says his pile is very biodiverse, and the heat it produces is likely great enough to destroy most diseases. He is willing to take that chance, mainly because he has a healthy, active, hot compost pile.
Reiners explains that efficient compost piles need a balance of high nitrogen greens and high carbon browns (straw, dried leaves, wood chips, etc).
So, if your compost pile is generating good heat, you might consider adding at least some diseased material, especially if you are limited in the amount of healthy material you have to add. Keep in mind that if the pile does not heat up enough, diseases can survive and reinfect your garden.
