Mycorrhizal inoculants for trees

dwheeler at dwheeler at
Tue Dec 30 02:21:14 EST 1997

Having already posted the Importance of Mycorrhizae in Forestry, let's
proceed onward to what mycorrhizae can be used in various applications of

First, most nurseries do not inoculate with mycorrhizae. This can explain
a portion of so-called transplant death of nursery stock when a low-land
nursery tree is transported to elevations above 2500 feet elevation. The
fungi found at 2500 feet are seldome the fungi found under 1000 feet

Estimated mycorrhizae with Douglas fir (Pseudotsuga menziesii) exceed
3,000 species. David Aurora in Mushrooms Demystified notes a considerable
number with oak trees in the western US. Western hemlock (Tsuga
heterophylla) is always associated with mycorrhizae when terrestrially
rooted. Other profoundly mycorrhizal tree species include pines, spruce,
true firs, and alder. The number of mycorrhizal species with most of
these species is not well understood or documented. The concept of fungi
being species specific: found only with one tree species, is recent.

Foresters must therefore learn what mycorrhizae are appropriate to given
slopes, elevation, soil, rainfall, and tree species. It is unlikely this
information will be quickly developed. Foresters can however, learn basic
fungal species and learn about whether these are generally saprophytes
(growing on wood), parasites (attacking wood) or symbionts (beneficial to
woody plants).

Most fungal species of Amanita, Scleroderma, Rhizopogon, Alpova,
Thelophora, Cantharellus, Boletus, Suillus, Leccinum, Tuber, Laccaria,
Tricholoma, and Cortinarius are probably mycorrhizal, even if they
haven't yet been cultured.

Parasites include species of woody conks. A live tree which has a conk
fruiting on it is likely a snag in the making.

Saprophytic fungi grow on rotting, dead wood. They include shiitake,
oyster, morels, Hericium, Grifola, Chicken of the Woods (Laetiporus
sulphureus), Marasmius, and others.

Most of my observations of fungi have taken place in Oregon, since this
is where I live. I have, over the past 12 years, attempted to grow about
50 species of fungi to date. Of these, I have been successful with about
40 species so far. Some mycorrhizal species such as Armillaria ponderosa
may take years to establish a mycelial network capable of producing

Many other fungi are quite easy to grow. Laccaria laccata I grew by
making a simple slurry of pureed sporocarps (mushrooms) in a food
processor. The slurry can be strained, and diluted in a backpack sprayer.
Individual growing trees can be inoculated on site by simply spraying
with this slurry near the roots. Preferably, this inoculation should be
done during rain or while the fungi are fruiting naturally. This ensures
that most of the natural conditions of inoculation are also at work. Most
of these conditions, such as soil organisms, are neither well known nor

Spore slurry works with many different species of fungi, but not with
truffles. People have been trying to cultivate truffles for thousands of
years. Only in the last century have several patents been issued for some
truffle species.

Rhizopogons are abundantly associated with pine and firs in a host of
different environments. The late Alexander H. Smith, after being
introduced as an expert in this genus of hypogeous (underground) fungi,
droley noted that in addition to have the largest collection of
identified Rhizopogons, he also had the largest collection of
unidentified Rhizopogons. Over 100 species of this genus are known to
exist. Many of them are found with specific tree species: Rhizopogon
occidentalis with Lodgepole and Ponderosa pine; Rhizopogon pinyonensis
with Pinyon pine; Rhizopogon sunrisensis with Madrone; Rhizopogon
vinicolor with Douglas fir. In addition, many of these fungi are found in
specific soil types: R. occidentalis with sandy soil; R. colossus with
sandy loam; R. parksii in humus-rich forest soils.

The Rhizopogons and Sclerodermas are among the easiest fungi I have found
to cultivate. I have grown R. villosulus, R. vinicolor, R. parksii, R.
colossus, and R. villescens with Douglas fir in Clackamas County, Oregon
at about 500 feet elevation. Sclerodermas have been grown with Douglas
fir, Italian Spruce-pine, Easter Red oak (Quercus palustra), Red alder
(Alnus rubra), Chestnut, English Walnut, Rhododendron, and oregano. Thus
Scleroderma species make desirable mycorrhizal inoculants for a wide
variety of trees. Unfortunately, they are also poisonous, so dried
sporocarps should be added directly to water before pureeing. Direct
inhalation of dried spores can be VERY DANGEROUS and possibly LIFE
THREATENING, similar to direct inhalation of puffball spores.

Foresters must way this against the growth potential that mycorrhizae
give trees. A Eastern Red oak in my backyard grew 3 feet the first year
when inoculated with Scleroderma cepa. A year later it had reached 8
feet, and I cut it at the base. The tree was quite persistent, and in the
6 years since has grown to nearly 40 feet tall, or around 6 feet per
year. Oddly, while this tree is considered a timber tree on the east
coast, in Oregon it is merely an interesting tree.

Rhizopogon rubescens is reported to be common in SE US Loblolly pine
plantations. I have personally never collected this species, and probably
wouldn't recognize Loblolly pine if I saw it. However, someone I know did
find a Rhizopogon rubescens in Southern Oregon at about 4-5,000 feet
elevation with White pine. A single Rhizopogon weighed 1.8 lbs. and had
sufficient spores to inoculate several _billion_ seedling trees in a
nursery situation.

I am interested in hearing what other common mycorrhizal fungi are found
by other foresters in other areas of the US.

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