Draft 9/27/01 Mike Amaranthus
Ten years ago the mention of mycorrhizal fungi
to a golf superintendent might have met with a blank stare. Today?s
managers are much more knowledgeable regarding the benefits of mycorrhizae.
Research studies have shown us all how these specialized fungi can
improve fertilizer utilization, rooting depth, the speed of establishment,
disease and drought resistance of turf.
The golf industry and golf managers take their responsibility for
managing the game and the environment seriously. New tools, such
as the use of beneficial mycorrhizal fungi, allow golf managers
to improve the condition of both turf and soil
Golf course management is a balance between the
speed of play, golfer?s desire to see perfectly manicured turf
grass and the ecological concerns of frequent chemical and water
use. Golf courses do not operate in a vacuum but are part of a watershed.
The selection of fertilizers, pesticides and water are important
not only to the "look" of the course but to the surrounding environment
as well. Golf course managers have a new tool in their belt that
utilizes nature?s own way for growing plants and conserving
resources. Golf course managers can use a group of beneficial soil
organisms, the mycorrhizal fungi, to improve the health and vigor
of their turf grass.
Most grass species in their undisturbed natural
environments form a beneficial association with mycorrhizal fungi.
The resulting structure is called a mycorrhiza, or literally "fungus-root".
Although several types of mycorrhizal fungi form mycorrhizae with
plants, the largest group, -endomycorrhiza or also called arbuscular
mycorrhizae form with most grass species. Mycorrhizal fungi are
present in soil as spores, as hyphae in soil (filaments) or as colonized
roots (Figure 1).
Hyphae of mycorrhizae penetrate into and between the outer cells
of the root. Inside the root the fungus forms special coiled hyphae
that provide increased surface area for exchanges of food to the
fungus and nutrients for the grass.
The mycorrhizal fungi once established on the
turf root system radiate out from the roots to form a dense network
of filaments .
These filaments form an extensive system of hyphae that grow into
the surrounding soil and provide a variety of benefits for the grass
plant. This network of filaments obtains 15 major macro and micro
nutrients and water and transport these materials back to the turf
root system. Mycorrhizae are especially important for uptake of nutrients
that do not readily move through the soil such as phosphorous and
many of the micro-nutrients. The elaborate network of hyphae beneath
the soil surface greatly increases the potential of the root system
to absorb nutrients and water. Conserving and incorporating fertility
and water directly into the target turf grass is a goal of golf management
professionals and minimizes off site and groundwater movement of fertilizer
that is not utilized. The network also binds soil particles together,
improves soilporosity and the movement of air and water within the
Soils in natural settings are full of beneficial
soil organisms including mycorrhizal fungi. Research indicates,
however, many common practices can degrade the mycorrhiza-forming
potential of soil. Construction practices, tillage, removal of topsoil,
site preparation, heavy use of pesticides and chemical fertilizer,
compaction, and leaving soils bare are some of the activities that
can reduce or eliminate these beneficial soil fungi (Amaranthus
et al. 1996; Doer et al. 1984; Dumroese et al. 1998). In many man-made
landscapes we have reduced or eliminated healthy diverse populations
of mycorrhizal fungi. (Figure
Putting greens constructed according to
U.S. Golf association standards lack mycorrhizal fungi at the time
of sowing and mycorrhizal populations are slow to increase in the
green (Koske et al. 1997). All important turf grass species can
form a specialized symbiotic (mutually beneficial) relationship
with mycorrhizal fungi. Unfortunately, modern golf construction
practices often reduce or eliminate these beneficial organisms).
New mycorrhizal products designed for the golf industry are now
returning these ancient allies of grass back to golf course soils.
Mycorrhizae are, by far, the most researched
aspect of soil biology. Over 48 thousand studies of the mycorrhizal
relationship with plants are available in the literature.
Studies have shown that grass species in the
family Poaceae benefit greatly from mycorrhizal colonization in terms
of growth and nutrient acquisition (Gemma and Koske 1989; Sylvia and
Burks 1988; Hall et al 1984)(Figure
5 & 6). Warm-season grasses such
as bermuda grass with coarse root systems are very dependent upon
mycorrhiza for sustained growth (Hetrick et al 1988; 1990). Recent
data indicates that cool-season, finer rooted bentgrass species also
form abundant mycorrhiza and benefit from the relationship, especially
where the phosphorous levels are not too high (Gemma et al. 1995;
Gemma et al 1997; Koske et al 1997). It is also well documented that
inoculation of grasses with mycorrhizal fungi in soil with low phosphorous
concentrations can produce greater shoot and root biomass (Hall et
al 1984; Petrovic 1984; Hetrick et al. 1986; 1988).
Recent findings of improved turf grass establishment,
root growth, fertilizer utilization, cover percentage, drought,
nematode and disease resistance has golf course managers including
mycorrhizal inoculations in their construction and maintenance practices.
Golf course greens incur environmental stresses caused by compaction,
frequent mowing, and artificial sandy substrates lacking nutrient
and water holding capacities. Mycorrhizae can benefit many plants
and results are often very apparent in situations where environmental
stress is high.
Attention has focused on water conservation as
water becomes a more expensive and environmentally sensitive component
of golf course management. Research studies have shown that mycorrhizae
can enhance the ability of grasses to avoid water stress (Koske
et al 1995; Auge et al. 1995; Allen et. al. 1991). Recent studies
from the Journal of Turfgrass Science indicate that creeping bentgrass
inoculated with the mycorrhizal fungus Glomus intraradices
tolerated drought conditions significantly longer than non-mycorrhizal
turf (Gemma et al. 1997). Mycorrhizal inoculated turf also recovered
more quickly from wilting than non-mycorrhizal turf. Mycorrhizal
turf maintained significantly higher (avg. 29% more) chlorophyll
concentrations than non mycorrhizal turf during drought events.
Other research studies indicate that greater chlorophyll content
and enhanced photosynthate production can lead to increased drought
resistance. Mycorrhizal inoculations can be a useful tool to managers
because sand/peat putting greens dry out quickly and creeping bentgrass
is intolerant of drought and difficult to maintain under summer
Research (Gemma et al, 1997; Green et al.
in preparation) indicates that mycorrhizal inoculation at the time
of sowing can increase the rate of establishment by turfgrass species.
The early establishment of turfgrass
in sand/peat medium has received the attention of managers where
early playability can have a significant economic payback. In recent
trials in Oregon and California, mycorrhizal inoculants at the time
of sowing doubled the percent grass cover in the early establishment
period.(Figure 7, 8, 9).
Root pathogenic fungi and parasitic nematodes
can be acute problems for golf course managers. Research indicates
that the mycorrhizal relationship can improve grasses resistance
to the negative effects of these organisms (Newsham et al. 1995;
Little and Maun 1996; Thompson and Wildermuth 1989, Linderman 1994).
Mycorrhizal fungi improve the plants resistance to soil born diseases
in several ways for a wide range of host species (Allen 1991; Linderman
1994). The literature of recent years, indicates that mycorrhizal
control of plant diseases may be strongly influenced by enhanced
nutrition. Other factors might also play a role, such as less availability
of resources for the pathogens, physical changes in roots and root
tissues, chemical changes of root and plant tissues, reduction of
environmental stresses, and increased concentrations of other beneficial
soil organisms around roots.
Some specific mycorrhizal fungi like Glomus
Glomus intraradices are particularly effective in preventing fusarium,
pythium, and phytophora infections (St-Arnauld et al 1995; Sitaramaiah
and Sikora 1981; Baghel and Bhatti 1990))
Root infections by pathogenic nematodes are generally
less severe on mycorrhizal plants than on non mycorrhizal plants,
but the responses may vary, and the mechanisms involved are being
studied (Linderman 1992). Symptoms of nematode infection are generally
reduced, and often, nematode populations themselves are reduced
(Hussey and Roncadori 1978; 1982). One reasonable proposed mechanism
is the improvement in turf grass vigor as a result of the mycorrhiza
relationship masks yield losses caused by nematode infection. Also,
changes in root exudates by mycorrhizae may change the attractiveness
of roots to nematode pathogens. Increased production of inhibitory
substances by mycorrhizae may additionally affect nematode population
and survival. Research has demonstrated mycorrhizal fungal species
Glomus mosseae and Glomus intraradices can help control the negative
impacts of parasitic nematodes (Pinochet et al. 1993; Calvert et
al. 1993; Zambolim and Schenck 1983; Chou and Schmitthenner 1974).
Sand/peat medium incorporated during construction
of golf greens is generally devoid of mycorrhizal inoculum (Gemma
et al 1997) and is a prime candidate for achieving the benefits
of the mycorrhizal relationship. Mycorrhizal inoculum can be incorporated
during construction and aerification. Mycorrhizal propagules are
then incorporated into the rooting zone where they will be effectively
Mycorrhizal inoculum should be incorporated
both spring and fall for several years until healthy populations
of mycorrhizae are established. Mycorrhizal colonization assessments
are simple tests now available at many soil testing laboratories.
Incorporating mycorrhizal inoculum during aerification is an appropriate
way of developing a mycorrhizal network in the soil even for greens
not inoculated during construction (Figure
Natural areas generally contain an array
of mycorrhizal fungal species. The proportions and abundance of
mycorrhizal species often declines following any disturbance. Not
all mycorrhizal fungi have the same capacities and tolerances. Because
of the wide variety of soil, climatic, and biotic conditions characterizing
golf environments, it is improbable that a single mycorrhizal fungus
could benefit all turf grasses and adapt to all conditions. For
example, the types and activities of mycorrhizal fungi associated
with grasses are often different than those associated with woody
plants. Mycorrhizal fungi have differing abilities to produce antibiotics
that retard soil pathogens. Likewise, some mycorrhizal fungi are
better at producing enzymes that facilitate mineral uptake such
as phosphorous and iron. Still other mycorrhizal fungi can access
organic forms of nitrogen. Selecting mycorrhizal products that contain
several mycorrhizal species likely provides a range of benefits
to the plant not found with only one species.
How often do you think about the impact of your
golf course maintenance practices on turf and environmental quality?
Annually? Weekly? Daily? If you responded weekly or daily you are
probably a person who is interested in organic, environmentally
friendly products that will improve turf and soil quality. Mycorrhizal
fungi are not new, trendy, genetically engineered organisms. These
specialized fungi have been fundamental to the survival and growth
of plants for over 400 million years. When you view turf grass at
a golf course it is like viewing an ice burg. Between 50 to 80 percent
of the energy absorbed by the grasses is allocated below-ground.
This energy can be put to work by the manager utilizing specific
beneficial soil organisms.
New scientific advancements in the cost effective
growing of certain mycorrhizal species beneficial to turf grass
are rapidly bringing mycorrhizal products to the golf management
marketplace. Mycorrhizae can help lower costs over the long
run. Healthy living soil and turf will retain nutrients, build soil
structure, reduce stress and suppress disease, thus reducing the
frequency and level of certain maintenance activities. Choosing to
incorporate mycorrhizal fungi into construction and aerification
programs will not only benefit the environment but improves turf
cover, rooting, fertilizer utilization, disease and drought resistance.
Protecting the environment has never made more sense. Myco-what?
This may be a question of the past.