Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
10/14/02
Contacts:
Christine Baker, Plant Pathology, 515-294-6570, cjbaker@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Oct. 18, 2002
Fungal friends
By Christine Baker
Plant Pathology Graduate Student
Iowa State University
In recent weeks, you may have seen a variety of mushrooms growing beneath the trees in your yard. Especially common in Iowa are slimy, yellow mushrooms that pop up in the fall under white pine trees. What are these mushrooms doing under your trees? Do they harm the trees? How can you get rid of them? Surprisingly, the homely fungi that grow under trees during the late summer and fall are often not harmful; rather, they may be your tree's best friends.
A mushroom is the short-lived reproductive structure of a large, thread-like fungal body that lives year-round in the soil and organic debris. Beneath the surface of the soil, these fungal threads are often attached to the roots of trees, providing the trees with extra nutrients and buffering them from stress. This association of a fungus with a plant root is called mycorrhiza (plural mycorrhizae).
"Mycorrhiza" means "fungus-root" in Greek and provides an intimate, mutually beneficial association between a fungus and a plant. The fungal partner extends long threads called hyphae through the soil, and around and into the roots of the plant. The fungus absorbs water and mineral nutrients from the soil, which it shares with the plant. Essentially, the fungus serves as an extension of the plant's root system. In return, the plant gives the fungus the sugar it needs to survive. Plants with mycorrhizae have better access to water and minerals and grow faster than plants without mycorrhizae, especially in nutrient-poor soils. The trees develop larger, healthier roots and are better equipped to handle stress, especially drought. In addition, mycorrhizae protect plants from root diseases and help to improve the soil structure.
Amazingly, this association is so beneficial to plants that approximately
90 percent of plant species, including nearly all trees, are known to
associate with approximately 2500 species of mycorrhizae fungi. Scientists
now think that it was mycorrhizal associations that allowed the first
terrestrial plants to leave the water and live in the harsh, dry conditions
of land -- paving the way for the evolution of all the land plants growing
today.
Not all mycorrhizal fungi produce mushrooms, and not all mushrooms that
grow below trees come from friendly mycorrhizal fungi. Mushrooms or shelf
fungi that develop directly on the tree itself are usually signs of decay,
and those that grow in "fairy rings" cause unsightly lawn problems
without any benefit.
A majority of mushrooms seen in yards arise from beneficial mycorrhizae. One of the most common mycorrhizal fungi in Iowa is Suillus americanus, the slimy, yellow-to- brown bolete (a mushroom with pores instead of gills) that grows under white pine. It is often called the "chicken-fat mushroom" for its color and slimy texture. Iowa is also home to several species of Russula, Lactaria and Cantherellus, which produce a variety of mushrooms under oak trees. Cantherellus, the edible, funnel-shaped chantarelle mushroom, produces its reproductive bodies in midsummer. The other fungi listed usually produce their mushrooms during late summer and fall.
How are mycorrhizae important to a home gardener? First, mycorrhizal mushrooms that grow below trees should be appreciated for the help they provide the tree. Applying fungicide to the soil damages the precious mycorrhizal associations helping to keep your tree healthy. If you cannot tolerate the mushrooms on your lawn, remove them by hand. The only way to permanently eliminate the fungus is to remove the tree! It is much easier to learn to enjoy the mushrooms during the brief times these helpful fungi make themselves visible.
Second, mycorrhizal fungi are abundant in most natural soils. Sterilized, compacted or highly disturbed soils (such as those in new housing developments) are often depleted of natural fungi and not conducive to mycorrhizal growth.
Several companies sell mycorrhizal inoculants, which are fungal spores in a powder or slurry that are applied to the soil or roots at planting. The inoculated fungi quickly develop mycorrhizal associations with the plant roots. These products may help trees and other plants become established in disturbed environments, such as in new landscape plantings. Inoculants are not usually necessary in natural soils, where other plants are growing well and the natural fungal population is healthy.
Although often unnoticed and unappreciated, mycorrhizal fungi are fungal friends that help to ensure the health, vitality and beauty of our valuable trees and landscapes.
-30-
ml: isugarden
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.