Q: Last summer, the mums in my beds got diseased with some sort of black spot. This spring, I dug them up and threw them out. I have noticed where they were planted, mushrooms have sprouted in those areas. Is my dirt diseased now? I want to plant some other things in those spots, but am worried they will become diseased also. If I get some bags of good dirt and mulch will that help my soil?
A: Before I answer the question about mushrooms in the soil, let’s discuss the black spot on your mums for just a bit. Since I can’t be sure which type of leaf spot your mums had, here is an overview of several types of leaf spot fungi and what to do for each:
- Leaf spots: Chrysanthemums can develop several leaf spot fungi, including Septoria chrysanthemi, S. chrysanthemella, Alternaria species and Cercospora chrysanthemi. Symptoms first appear as yellow spots that turn brown to black. Spotting usually takes place on lower leaves first. The affected spots can grow larger and eventually cause death of the entire leaf. To control, regularly clean up and destroy infected plant debris and always hand pick affected leaves from lightly infested plants. Avoid splashing water onto plant foliage and water early in the day only so that the foliage dries quickly.
- Bacterial leaf spot Pseudomonas cichorii: Evidence of bacterial leaf spot includes tan to dark brown spots or blotches that are often circled by yellowing tissue. Discoloration may be prominent along leaf veins because bacteria growth is limited by major veins. Leaf wilt and death often follow. Bacteria remains in or on infected plants, plant detritus, any contaminated seeds or soil and pots and tools that came into contact with the plant. The plants cannot be cured. Control this disease by choosing pathogen-free cultivars, resistant varieties, good sanitation and no overhead watering or handling of the plants when they are wet. Once plants become infected with bacteria, pull out the infected plants and those near them to prevent spread of the disease. Dispose of the plants in the trash, not on the compost pile.
As an aside not related to leaf spotting, if your plants are infected with verticillium wilt, avoid planting anything in that area for several years.
Now as to the mushrooms growing in the soil: Mushrooms are the reproductive structures of fungi, and The Oregon State University Extension reports that more likely than not, mushrooms indicate a healthy soil suitable for trees and other plants to grow in.
Fungi and bacteria play a vital role in the soil structure in that they break down complex organic compounds of proteins, carbohydrates and fats into their most basic elements that can be used by other generations of organisms. Since plants cannot chew food or digest it, fungi and bacteria do this job for them. Plants produce sugars during photosynthesis that, in turn, feed soil organisms.
Most native and landscape plants depend on fungi and other processes for optimal health and growth.
In a nutshell, fungi produce microscopic filaments that can reach deeply into the soil.
A tablespoon of soil can contain miles of these filaments, known as mycorrhizal filaments. They are not a fertilizer.
Rather, among other benefits, these filaments produce organic compounds that help to improve soil structure for better plant root growth. They also can suppress soil-borne pathogens and protect plants from root diseases.
Over-watering, over-fertilization and use of fungicides can potentially kill the filaments or hinder their usefulness, which is something you don’t want to happen.
There is no need to add more soil in an effort to eliminate the mushrooms, and the soil should be just fine for planting. Even so, and regardless of their benefits to soil, you might want to remove mushrooms from your garden if you are worried they could be poisonous or otherwise be harmful to children or pets. Simply scrub them off with a rake and bury them in the compost pile. Another crop will probably spring up, but after a while, the mushrooms will stop sprouting.
For more information, call The Ohio State University Summit County Extension Hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3, and request Fact Sheet HYG-3304-98, “Control of Nuisance and Detrimental Molds (Fungi) in Mulches and Composts.”
Please note fact sheets are sent out free; there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at the public library.
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to firstname.lastname@example.org, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.
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