Endophytic Grasses for Turf
Full speed ahead or proceed with caution?
Endophytic turf grasses have become widely available only in the last few years. They are intended to mimic natural control of pests and reduce reliance on chemical inputs. However, we are only just beginning to understand how endophytes function in natural communities where endophytic plants and herbivores (plant eating animals including insects, birds, mammals) co-evolve over long periods of time. Currently, there are several reasons for suggesting some caution in promoting endophytic turf grasses and in using them. These include the toxicity of endophytic grasses to livestock, their potential to become invasive species, loss of endophytes in stored seed, and possible poor performance of endophytic turf grasses compared to alternative cultivars and species.
Since the early 1990s use of commercially developed or selected "endophytic" grasses has been widely promoted as a means of combating chinch bug and other pests in turfs (including lawns, golf courses, right of ways). [E19, E20] Pests may consume the endophytic grasses and be killed or harmed by the toxins, or may avoid them, depending on the cultivar and the pest. [E1, E2, E17, E18]
What are endophytic grasses?
Tissues of commercially distributed "endophytic" grasses are colonized by fungi of the genus Neotyphodium. These fungi do not cause any obvious damage and may confer certain benefits to the grasses including increased resistance to pests and diseases and to some environmental stresses such as drought, mineral stress and soil aluminum or acidity. [E22, E23, E24] The same types of associations opccur naturally. The fungi are transmitted to new plants via infected seeds from an endophytic parent plant, so called "vertical transmission". These fungi do not produce spores and apparently do not survive or propagate outside of living plant tissues. "Horizontal transmission" - from infected to uninfected plants - does not occur or is very rare in nature. [E24, E22, E27] The associations tend to be quite specific, the fungi infecting certain species and cultivars of grass and not others, also there are many different species and strains of the fungus. [E23, 24] An individual cultivar could carry an endophyte (designated E+) or not carry (E-) an endophyte. Within horticulturally produced and managed lines, it appears that once an E+ type is established successfully in the field, the association is quite stable, i.e., offspring from the initial plants, whether produced vegetatively or by seed will also be E+; conversely, E - types remain devoid of endophytes.[E22] However, the endophyte could be lost during storage of seed, hence a cultivar developed and sold as an E+ cultivar could turn out to function as an E+ cultivar in practice. (Conversely, an E- minus cultivar might carry a few contaminated seeds whose offspring multiply and become dominant under grazing or pest pressure in the field, turning an E- stand into a predominantly E+ stand.) Presence or absence of the endophytes is determined by microscopic examination of the plant tissues or by lab tests for compounds produced by the endophytic fungus.
The mechanisms by which endophytic grasses deter pests are quite well understood and are related to the production of alkaloids by the fungi. Unfortunately, in some cases those include alkaloids that are toxic to grazing animals. [E22]
Also, improved performance under low maintenance situations makes some of the endophytic forms good candidates for low maintenance uses such as on roadside right of ways and in parks. The endophytic tall fescue variety Kentucky 31 has been widely used in the U.S. for this purpose since the 1940s.[E21] Tall fescues are considered a rather coarse species for lawns, however, there are now many endophytic cultivars of ryegrass on the market and more limited numbers of creeping red, hard and chewing fescues. [E19] Endophytic cultivars are not yet available for Kentucky bluegrass and creeping bentgrass but patents have apparently been taken out on such grasses by Jacklin Seed Co. in the U.S. [E3]
Endophyte mycelium in tall fescue leaf tissue.
(Photo by Nick Hill, courtesy USDA: ARS
Unfortunately, this seemingly very positive development within the turf industry has some actual or potential downsides.
Toxic alkaloids in tall fescue can make cows sick. The cow in the foreground has consumed so much of these compounds that she is ill.
Photo by John Stuedemann, courtest of U.S.D.A./A.R.S.
Toxicity to livestock
It has been known since the late 1940's/early 1950's that the Kentucky 31 tall fescue variety is highly toxic to cattle and horses, and to a lesser extent to sheep.[E5, E14, E25]. Tall fescues were introduced to North America from Europe, probably in the late 1800s. The Kentucky 31 variety was obtained from a vigorous tall fescue stand on a Kentucky farm in 1931 and widely planted as a forage and for erosion control before its deleterious properties were recognized. It wasn't until 1977 that endophytic fungi were identified as the agent responsible for the toxicity. At about the same time, a similar type of livestock toxicity caused by perennial ryegrass in some pastures was likewise shown to be due to endophytic fungi. The logical solution was to establish forages using endophyte-free (E-) seed. To the surprise of researchers, in side by side trials these E- types, although not toxic to livestock, proved to have reduced vigor and resistance to pests compared to the endophytic E+ types. That discovery in turn led to elucidation in the 1980s (and continuing) of the many beneficial properties associated with the endophytes in grassses. [E22]
The somewhat curious outcome of these discoveries is that the livestock industry is promoting endophyte-free tall fescue and ryegrass for forages [E13] while the turf industry is promoting endophytic types. Although most researchers in the area seem well aware of the dual nature of the endophytes (good for the grass, but harmful to livestock), it seems that many personnel in the turf industry and probably most consumers are not aware of potential hazards of endophytic grasses for livestock and that endophytic types should NOT be planted in turfs adjacent to hay and pasture lands. This issue is relevant to Nova Scotia as ryegrass is an important forage species here. (Tall fescues do not overwinter well in Nova Scotia so are not in general use here.)
DO NOT PLANT RYEGRASSES|
ONLY FOR LAWN USE IN PASTURES!
This alert is on a website of a company marketing ryegrasses for both pasture and turf ( www.ryegrasses.com).
Unfortunately, a similar warning is NOT found on many extension bulletins promoting endophytic ryegrasses for turf or on many websites and brochures advertising endophytic grasses for turfs.
One approach to dealing with the livestock toxicity problem is to find or engineer fungal strains that (in combination with the host plant) produce the alkaloids that confer benefits to the host including deterrence of herbivores, but not the ergot alkaloids that are toxic to livestock; these strains can then used to infect the grass cultivars in place of the original strains, so affording the benefits of the endophytes without the detriments.[E25, E22] Several of these 'novel associations' are now marketed commercially. One follow-up study found that they may not be performing as well as had been anticipated and could exacerbate certain pest problems; the authors comment: "Over-reliance on specific grass-endophyte combinations is, perhaps, a risk-laden strategy." [E40]
Negative effects on biodiversity
Tall fescue is also an "environmental weed" or "invasive species" in much of the U.S., and there is good evidence that its invasive properties are associated with or accentuated by endophytic fungi. [E9, 104] An invasive species is one that "becomes established in natural or semi-natural ecosystems or habitats, is an agent of change, and threatens native biological diversity". [E25].
The U.S. National Park Services describes tall fescue as follows.[E26]
Tall fescue invades native grasslands, savannas, woodlands and other high-light natural habitats. In the Midwest, many thousands of acres of native prairie have been seeded with tall fescue for well meaning but misguided conservation purposes. In the Ozarks, woodlands and barrens were converted to tall fescue pasture to enhance grazing income. Some varieties of tall fescue, including Kentucky 31, harbor a mutualistic fungal endophyte (Neotyphodium coenophialum) that gives it a competitive advantage over some plants, including legumes. As a result, communities dominated by tall fescue are often low in plant species richness. In addition, alkaloids produced by endophyte-infected tall fescue may be toxic to small mammals and of low palatability to ungulates (such as cattle, deer and elk). Many ground-nesting birds, including Bobwhite quail (Colinus virginianus), are unable to use tall fescue fields as foraging or nesting habitat because of a lack of habitat structure and vegetation composition.
In addition to the issues cited above, endophytic plants can have direct negative effects on birds [E10, E29] and small mammals [E6] and indirect effects on the species composition of food chains. [E30]Such effects and interactions also occur naturally, but the combination of exotic grasses (most of turf species used in North America are not native to North America) planted over large areas and primed with high levels of endophytes may make endophytic grasses promoted for turf particularly potent, potential invasive species.
(The variety Kentucky 31 cited above is widely used in the turf industry.)
It is difficult to predict whether an individual variety or cultivar might become invasive, and certainly, endophytes are not required for invasiveness. However, they appear to enhance invasiveness of some grass species. E9, E31 Further, ecologists have concluded that "propagule pressure" is a major factor in invasiveness, E32 also economic development. E33 Thus the more widespread the use of novel types of endophytic grasses, the greater likelihood that one or some of the new endophytic types developed for turfs will become serious invasive species. Spyreas et al. E34 suggest "using extreme care when planting highly vigorous, potentially herbivore resistant cultivars like KY-31 adjacent to natural areas".
[E6, E10]. (Although the turf industry/research community is beginning to give some attention to invasiveness of turf grasses, E35 invasiveness is not commonly identified as a potential environmental impact of turf culture (cf USDA identified Priority Turf Research Needs E36 and warnings of this sort have not to date been part of information packages and advertisements for endophytic grasses.)
Even for lawns considered on their own, there are some potential complications associated with use of endophytic grasses.
- Storage conditions affect the levels of endophytes in seed.[E19, E24]
"The fungus does not survive in seed in hot conditions. In agronomic systems, the fungi may die out if the seed is stored for longer than 6 months, much less if the temperature of storage exceeds 36oC for more than 6 hours. Many so called "endophyte" seed stocks lack the fungus because storage conditions are primitive and seed is often kept for long periods." [E24]
Hence a consumer might purchase seed of an E+ endophytic cultivar that turns out not to be endophytic and performs more poorly than alternative E- cultivars that might have been seeded.
In an undated study by Landscape New Brunswick and Maritime MicroBiologicals Inc. only 35% of viable
seed of endophyte enhanced perennial rye and 60% of chewings fescue variety "T" actually contained endophytes. None of the seed of chewings fescue contained endophyte after storage for 5 months; approximatley 25% of the perennial rye seed contained endophyte after 5 months, and none contained endophyte after 10 months of storage. [E43]
- Cultivar characteristics affecting establishment and local persistence sometimes should have priority over resistance to chinch bug (or other pests). [E15]
- Endophytic ryegrass suppresses white clover compared to endophyte-free ryegrass. [reviewed in E23] ] White clover is a very important species in ecological turf management (see other pages on this site).
"In all likelihood, the grass-endophyte symbioses observed in nature span a continuum of interactions from antagonistic to mutualistic.. That is, the nature of the grass-endophyte symbiosis is contingent on environmental conditions, even for a single host species. -
G.P. Cheplick [E41]
"Our experience of these [beneficial] effects is limited. They depend on
the genotype of grass, the strain of endophyte and the
conditions under which the plants are grown. The extra
vigour of the ryegrass plants, and possibly chemicals
produced by the grass/endophyte combination, may reduce
the productivity of companion legumes in mixed swards." Paul Quigley & Kevin Reed commenting on endophytic ryegrass in Australian pastures [E42]
- Inconsistent relationships between endophyte presence and benefits of endophytes: some endophytic (E+) types of particular cultivars may be more attractive to chinch bug or other pests or be less drought resistant than the non-endophytic (E-) types.[E4, E18, E28, E23] Also site conditions can influence resistance to pests and stress resistance. 
- Choice/mixed species selection problems Endophytic forms are not available for Kentucky bluegrass, a key component of most turfs. Tall fescues may not blend well with other species, and does not persist well in some areas (e.g., Nova Scotia). There are currently relatively few E+ fine fescues available. This leaves perennial ryegrass as the cornerstone endophytic species for most lawn situations. Research by to Shetlar and associates [E3, E15, E37] indicates that "Endophyte levels need to be around 40% of the stand to cause a significant reduction of surface insect pests - sod webworm, chinch bug and billbug." [E3] Unless there persistent pest pressure (which would tend to favour the E+ types and cause them to increase in abundance even if they are initially at low levels), repeated overseeding or complete renovation of a lawn could be required to achieve these levels. In northern areas, perennial ryegrasses tend to have persistence problems, also as noted by Shetlar [E3] they are subject to rust and greyspot leaf diseases which are increasing. He also comments "Perennial ryegrass may not match the existing turf - lighter green and glossy. (Pick a dark green cultivar.)
In short, leaving aside the other limitations already discussed, depending on what E+ cultivars are available, it may be difficult to find an effective, esthetically acceptable combination of endophytic and non-endophytic grasses for the purpose of increasing resistance of a turf to pests. It would certainly be unwise to bank on this approach alone as means of controlling pests. On the other hand, overseeding some E+ ryegrass into a lawn and letting nature take its course (it might or might not increase and persist and prove effective) would not be an expensive experiment. If local lawncare professionals can demonstrate situations where their use of E+ grasses has been effective, then their services might be worth considering!
Endophytic turf grasses have become widely available only in the last few years. Their promotion is a well intentioned and intended to mimic natural control of pests and reduce reliance on chemical inputs. However, we are only just beginning to understand how endophytes function in natural communities where endophytic plants and herbivores co-evolve over long periods of time. [E9, E16, E27, E34, ] There is a tremendous amount research being conducted on all aspects of the associations and in the long term they could become a predictable and environmentally desirable component of grass management. (My reason for some reservation that this will happen is the possibility, perhaps even the likelihood, that this goal will be sought through genetic engineering of both the grass and endophyte, indeed that process has already begun [E38, E39]. ) Regardless, at this time, there are several reasons for suggesting some caution in promoting grass endophytes and in using them in turfs.
Fortunately, as outlined on other pages on this website, there are other means for sustainable pest management of pests in lawns and other turfs, thus refraining from reliance on purchased endophytic grasses for pest control does not mean one has to accept high levels of pests!
- Purchased seed advertised as endophytic could be lacking the endophytes because of storage conditions; consumers should inquire about the sources and storage of seed, ensure proper storage and use received seed within a few months or less. If large areas are to be seeded, consumers should seek confirmation that seed contains viable endophytes before using it. See
- There may be some variability in the effectiveness of endophytic cultivars in reducing pest problems according to the particular cultivar/endophyte combination and the site conditions; thus users might look for local examples of successful use of the particular endophyte/culitvar combination.
- E+ turf cultivars should not be planted in areas where livestock graze pastures or consume locally grown hay
- E+ turf cultivars should not be planted adjacent to natural grasslands or biodiversity conservation areas.
|- David Patriquin |
Professor of Biology, Dalhousie University.
Posted 18 May 2004
Revised 27 Jan. 2006
References and Links
The sources cited above can be found on the References Page for this website. A comprehensive, multi-authored book and a few documents that can be accessed readily via the web are given below.
Neotyphodium in Cool-Season Grasses
Craig Roberts, Chuck West, Don Spiers (Editors). 2004. 352 pages, Blackwell Publishing.
"This book will be an up to date compilation of the latest knowledge on the genus Neotyphodium including the molecular biology, their effects on their grass hosts, invertebrate and vertebrate herbivores, and the plant communities in which they interact. It also includes information on the commercial uses of endophytes in livestock and turf industries."
See http://store.blackwell-professional.com/9780813801896.html (Viewed 16 May 2007)
- Introduction to Fungal Endophytes of Plants
University of Sydney, School of Biological Sciences
Computer Based Learning Resources, Spons. (Viewed 16 May 2007)
- Debunking Endophytes
(www.omafra.gov.on.ca/english/crops/facts/endophyt.htm) Ontario Ministry of Agriculture and Food, Spons.; P. Pam Charbonneau, Auth. (Updated November 2005. Viewed 16 May 2007)
"The word endophyte keeps cropping up in magazine articles, talks and in seed advertisements. Associated with it are all sorts of claims of insect resistance, stress tolerance, etc. This article will attempt to give you the facts as well as point out some precautions when buying seed containing endophyte." Includes a regularly updated list of Ontario turfgrass varieties containing endophytes, information on storage. (There appears to be an error in the document: endophytic cultivars of Tall Fescue are listed under Creeping Bentgrass for which commercial cultivars have not yet been released. )
- A good infection
Article in Grounds Maintenance, by Kevin N. Morris (2001 Feb 1. Viewed 16 May 2006).
- Toxic Endophyte-Infected Tall Fescue and Range Grasses: Historic Perspective (PDF document)
(www.asas.org/jas/papers/1995/mar/MAR0861.PDF). Paper by CW Bacon, 1995, in the Journal of Animal Science, Volume 73 pp 861-870.
- Weeds Gone Wild: Alien Plant Invaders of Natural Areas
(www.nps.gov/plants/alien/) National Park Service (U.S.A.), spons. (Viewed 16 May 2007)
" a web-based project of the Plant Conservation Alliance's Alien Plant Working Group, that provides information for the general public, land managers, researchers, and others on the serious threat and impacts of invasive alien (exotic, non-native) plants to the native flora, fauna, and natural ecosystems of the United States,"; includes Tall Fescue.
Posted 18 May 2004
Major revision 27 Jan. 2006
Links checked 23 May 2007