EGARDENING               Last modified December 12, 2006

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Mycorrhiza
by Catherine Kavassalis

I know a bank where the wild thyme blows,
Where oxlips and the nodding violet grows,
Quite over-canopied with luscious woodbine,
With sweet musk-roses and with eglantine:
There sleeps Titania sometime of the night,
Lull'd in these flowers with dances and delight.


"A Midsummer Night's Dream" (2.1.255-60)

Mycorrhizal fungi forming a tethered fairy ring.

"Out, damn’d spot! out, I say!" Lady McBeth was not of course speaking of black spot on her roses. But, perhaps, had Shakespeare's sweet musk-rose been so afflicted, he would have penned a different tale. Fungal infections have certainly been around since well before Elizabethan times, and farmers and gardeners alike have had to battle fungal blights for centuries.  Most gardeners rue the growth of fungi in their yards, but not all fungi are a bad thing.

Last fall, as the trees began to send their photosynthate below-ground to their root system for winter storage, mushrooms began shooting up throughout my yard. In past years, I had removed these fungal fruits as soon as they appeared, not realizing what a pretty picture they would make. Picking off the mushroom fruits doesn't affect the body of the fungi, its mycelium, growing beneath the ground (but it can reduce their spread). As I took a closer look at what types of mushrooms were growing, I realized that I was cultivating a varied population of beneficial mycorrhizal fungi. 

A mycorrhiza is a highly evolved mutualistic association between soil fungi and plants. The term mycorrhizal comes from the Greek words myco, meaning fungus, and rhiza, meaning root. Mycorrhizal fungi produce root filaments called hyphae in close association with the roots of photosynthesizing plants. These fungal filaments in the soil act as an extension of a plant's root system and help that plant to absorb water and nutrients. They may also provide plants protection against pathogens and insect attack. In return the fungus receives photosynthetically derived nutrients from the plant. It is believed that the majority of plant families are benefited by mycorrhizal associations. For those of you interested in the more scientific details of mycorrhizas, I highly recommend Mark Brundrett's comprehensive Introduction to Mycorrhizas:  http://www.ffp.csiro.au/research/mycorrhiza/intro.html.

Although most plants can survive in the absence of mycorrhizal fungi, they are healthier when they are supported by their fungal friends. You can help support this relationship by first and foremost not using fungicides as part of your regular garden practice. How then do you deal with the nasty infections associated with parasitic fungi?

First, planting disease resistant species, like Shakespeare's musk rose, Rosa arvensis, is always a good idea. Next, practice good garden maintenance. Allow for air circulation around susceptible plants, water at the base of susceptible plants, and remove infected plant material to prevent spores from spreading the disease. Also you can try a bicarbonate spray (1 liter of water, 3 tsp. of bicarbonate of soda and some fish emulsion) when fungal growth first appears.  Finally, encourage the growth of beneficial fungi. 

Some mycorrhizal inoculates are becoming available through garden centers and can be added at planting time. A rose bush inoculated with the appropriate mycorrhizal fungi is far more able to thwart off an attack by the fungus Diplocarpon rosae (a black spot producer) than one in sterile soil. However, be aware that there are numerous mycorrhizal fungi and some are extremely host specific, so you must match the type of inoculate to the particular plant, shrub or tree of interest. Note that many mycorrhizal fungi do not produce mushrooms, so you will never know they are there. You can promote their growth by not tilling too deeply around root systems and by using plenty of organic matter in your garden. Also, you might consider leaving a few of those cute toadstools (as long as they're not the truly toxic ones) to grow in your yard - some are just lovely. Thus, I would like to encourage you to become like Shakespeare's elves: “By moon-shine do the green sour ringlets make… you whose pastime is to make midnight mushrooms.” The Tempest (5.1.42-44)

May toadstools nestle in your flower beds and help you tend your beauties in the spring.

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