Authors: Don Pitcher, Mary J. Russo, Global Invasive Species Team, The Nature Conservancy
- 1 STEWARDSHIP SUMMARY
- 2 NATURAL HISTORY
- 3 CONDITION
- 4 MANAGEMENT/MONITORING
- 5 RESEARCH
- 6 INFORMATION SOURCES
General Description: Holcus lanatus is a grayish, soft-pubescent, fibrous-rooted perennial grass.
Diagnostic Characteristics: Holcus lanatus is rarely mistaken for any other species with the possible exception of H. Mollis, H. lanatus can be distinguished by the purplish coloration on the panicles and veins of the sheaths, soft hairs all over, and lack of rhizomes. The two species may be able to hybridize.
Holcus lanatus is a perennial grass, native to Europe, which was brought into California as forage. It escaped from cultivation and has become a weed species, particularly in the California Coast Ranges. Velvet grass frequently occurs on poor, moist soils. It is a prolific seeder and can exist in the seed bank in large numbers. It can also reproduce from decumbent tillers. Holcus lanatus is an aggressive weed and can become dominant if not controlled. The most effective control measure is physical removal by hand pulling or hoeing. Mowing or grazing used in combination with prescribed burning may also reduce the plant's dominance.
Velvet grass is of European origin, its center of origin thought to be the Iberian peninsula, and is a native of temperate areas of Europe and Asia. It was probably introduced to North America either accidentally as a contaminant of forage seed or deliberately as a component of seed mixtures for meadow. It has since spread and become locally abundant from British Columbia to Nova Scotia, Canada, south from Maine to Kansas and Colorado, south to Georgia and Louisiana and in primarily moist areas below 7500 feet along the Pacific Coast from British Columbia to California and to Montana and Arizona.
Velvet grass is common throughout Europe except the extreme north and northeast where it is only casual. In England, it is widely distributed in fields, particularly on north-facing slopes. The grass is now found throughout Asia, Africa, New Zealand, Australia, and sub-Antarctic islands. It has escaped cultivation and become a weed pest along roadsides, fencerows, ditch banks, in old pastures, and other disturbed sites, particularly in moist places. In the Coast Ranges, it has become a weed of minor importance.
Holcus lanatus exhibits a wide climatic tolerance of temperate regimes over a wide range of altitudes (0-1500m). It is killed by severe frost. Optimal growth occurs under moist conditions; however, it grows well in very wet conditions and can survive moderate periods of drought.
In Britain H. lanatus occurs on a wide range of soil types including those of rich-fen and fen-meadow communities, poorly drained, waterlogged, low to moderately fertile, and nutrient-rich soils. It occurs independent of soil phosphorous content and grows well in potassium- and/or nitrogen-poor soils. It tolerates a wide range of soil pH, growing best between pH 5.0 and 7.5. Studies in Oregon indicate an increase in the abundance of velvet grass under mildly acidic conditions.
Little research has been done on Holcus lanatus in North America. In Europe, it is an adaptable, competitive species that tolerates a wide range of habitats, particularly acidic, low nutrient sites.
GROWTH, PRODUCTIVITY, AND COMPETITION
In the Soviet Union, Trapaidze and Gogiya (1981) report that Holcus species have an exceptionally long growing season. Germination occurs from seed or as sprouts from roots in late autumn, with flowering between May and July. In a Dutch experiment, velvet grass leaf area peaked 15 weeks after sowing, and maximum dry weight was attained two weeks later. In the later stages of growth, root mass increased dramatically, reaching half of the total plant weight. Nitrogen levels also showed a marked increase after 15 weeks of growth. Nitrogen availability may be the limiting factor in Holcus lanatus growth (Watt 1978). Holcus lanatus normally occurs on soils of moderate to low fertility, but fertilization appears to improve its competitive ability.
High water table levels reduce the productivity of velvet grass. Holcus manages to persist on these wet sites by producing a large number of fine roots on the soil surface where aeration and nutrient levels are higher. Grootjans (1979) noted that a lowered water table increase the N-mineralization rate and the nitrate content leading to a strong site dominance by Holcus lanatus. Severe winter weather and high ground water can kill the grass, perhaps by lowering the N-mineralization rate. Velvet grass can tolerate soils with a pH range of 3 to 8.1 but does best on sites with a pH of 4.5 to 5.5.
Like other weeds from disturbed but productive habitats, Holcus lanatus is able to grow rapidly. The mean recorded growth rate is 1.56 g/g.week while the maximum growth rate exceeds 2 g/g.week. This rapid growth may indicate a high potential competitive ability among crop and weed species. This aggressiveness is shown in the dominance of velvet grass in English pastures. Holcus also does well in both high and low levels of light.
In an English study, Remison and Snaydon (1980) found that Holcus lanatus outcompeted Dactylis glomerata (orchard grass) under a wide variety of conditions. Velvet grass yield increased by 50% on sites with competition over sites where it was grown alone. Similar results are reported for competition between Holcus lanatus and Lolium perenne (ryegrass). Velvet grass is particularly aggressive in root competition due to its higher proportion of roots than other British pasture species.
In a Dutch grassland study, Holcus lanatus became dominant when the grass was mowed following maturation and seed dispersal. When earlier cuts were made, Holcus lanatus survived but became less dominant. Holcus lanatus responds well to cutting, even when cut back to only 2 cm above the ground. On unharvested sites, velvet grass gradually forces other plants out, reducing species diversity. This process is particularly apparent on unfertilized sites. Allelopathy may also play a role in the dominance of Holcus lanatus over other grasses.
In North America, flowering occurs June through August (September). H. lanatus is wind pollinated and predominantly an outcrossing species. Successful self-fertilization occurs only occasionally and is impossible in some plants. During anthesis the panicle opens from the apex down and closes likewise.
In England, Holcus lanatus seeds are shed from June to September. The plants require vernalization to flower, but this process is enhanced and, to a small extent, replaced by short-day treatment. It flowers and produces seeds from the second year onwards and behaves as a "paucennial." In places with reduced competition, the plant will often die after a few years, particularly following luxuriant flowering. In southern Europe, very short-lived races that flower the first year are found in dry habitats. In northern races, the plants require a period of vegetative growth prior to flowering in the second year. Holcus lanatus also exhibits variation in culm length and growth habit. In exposed maritime habitats, it grows as a low plant, while farther inland, the plants are more erect with tall culms.
Trapaidze and Gogiya (1981) report up to 850 wind-dispersed seeds per plant in the Soviet Union. In England, Watt (1976) found production of up to 240,000 seeds per plant, most of which germinated shortly after landing on moist soils.
Williams (1983) found that when stored under dry, shaded conditions, velvet grass seeds remained viable for at least 48 weeks with 90-99% germination. Trapaidze and Gogiya (1981) found a germination rate of 95% for the first two years after seed harvest. Both vertebrates and earthworms appear to significantly reduce velvet grass populations by their burial or consumption of seeds. When the seeds were buried, only 3% of them were still viable after a year. Seeds buried at a depth of 1-2 cm had a much higher chance of emergence than those at a depth of 3 cm. In the Soviet Union, Holcus seeds showed 87% germination rate on the ground surface, 76% at a depth of 1 cm, and only 5% germination at 2 cm. Holcus lanatus seeds are thus apparently not innately dormant, though certain field conditions may enforce dormancy. Even though most of the seeds are nondormant, the potential number of seeds produced by each plant is so high that even a 1% level of innate or enforced dormancy would result in a large amount of buried viable seed. The species can thus exist in large numbers in a seed bank, even if it is not an important plant on a given site.
Seed germination can occur at 7-8° C. Thompson and Whatley (1984) suggest that burying the seeds may induce a requirement for fluctuating temperatures of greater than 19° C. The result is that Holcus lanatus seeds germinate more readily in larger canopy gaps (wider than 25 cm) where their survival chances are improved. Mortimer (1976) estimates that when various mortality factors are taken into consideration, each Holcus lanatus plant can produce 9.9 adult plants the following year.
Holcus lanatus is not usually considered a stoloniferous species, but regeneration can occur by the formation of decumbent tillers in late summer that subsequently produce roots and shoots at the nodes. Growth of these shoots may be enhanced by grazing or mowing, but root growth does not appear to be affected.
Holcus lanatus is present on Oregon and Washington westside grassland preserves and the Northern California Coast Range Preserve. It is apparently not a major problem species on Nature Conservancy lands in California, but where it occurs, control may be difficult due to its prolific seeding ability and its possible allelopathic effect on native grasses. It has, however, become a major problem on western Oregon and Washington grassland preserves.
With the right combination of control measures, it should be possible to eliminate velvet grass from selected areas. Constant monitoring of previously infected sites will be necessary since it can quickly become dominant on a site.
Control of velvet grass requires active management once it becomes established in an area.
Hoeing or hand pulling Holcus lanatus plants are effective, albeit time-consuming, control methods. Intensive mowing or grazing suppresses the establishment and spread of velvet grass on a site. However, low intensity grazing may allow invasion of pastures. Haggar and Elliot (1978) found that H. lanatus increased from 18 to 43% of the total herbage over four years at a low stocking rate. The effects of grazing on velvet grass can be influenced by associated species and nutrient status. Holcus lanatus is also susceptible to damage from heavy treading by stock.
Control of the grass is most effective when it is cut prior to seed dispersal. Elimination of the plant will be difficult, however, due to its perennial nature and ability to regenerate from decumbent tillers even when cut to only 2 cm above the ground surface. The enormous Holcus lanatus seed bank means that the grass can quickly re-establish itself after any disturbance, so careful monitoring is needed.
Holcus lanatus is considered a "low-fertility species". Studies in Oregon showed that nitrogen application reduced relative abundance. However, Haggar (1976) and Elliot et al. (1974) documented a positive response to nitrogen fertilization.
Burning has a deleterious effect on velvet grass under some conditions. It is particularly effective in controlling the grass when combined with grazing.
Very little research has been done on controlling Holcus lanatus with insects or phytotoxins. Most insect predators of the weed also attack other, more desirable grass species. No list of insects preying on Holcus lanatus exists for Canada. However, Beddows (1961) has compiled one for British populations which includes various species of leafhoppers, butterflies, and flies.
Holcus species are hosts to the fungus Gaeumannomyces graminis which also infects wheat and barley, so it is unlikely to be used to control Holcus. Holcus lanatus is a host to the club-root disease Plasmodiophora brassicae which also infects several important vegetable crops. Toms (1964) and Conners (1967) listed the following plant virus and fungus parasites from Canada: twist (Dilophospora alopecuri), leafsmut (Entyloma dactylidis), crown rust (Puccinea coronata), rust (P. recondita), stripesmut (Ustilago striiformis), Epicholoe typhina, and Helminthosporum triseptum. Lists of fungi that infect velvet grass in Britain are compiled in Beddows (1961).
Holcus lanatus is susceptible to a variety of herbicides, but not all are safe or legal to use. Near streams or lakes, particular caution should be taken when using herbicides. Prior to using any herbicide, check with the County Agricultural Commissioner to determine which chemicals are legal to use in a given situation. The labels should also give more precise information on proper mixing and safety precautions. A certified Pest Control Applicator should be hired for large jobs or those requiring non-selective herbicides.
Dr. Jim McHenry (1985) of the University of California, Davis, recommends the use of Dalapon® (Dowcon™) to control Holcus lanatus on California preserves. For perennials such as velvet grass, spraying should be done in spring when the seed head first appears. This results in better translocation of the herbicide into the root system. Dalapon® will also kill other grasses and can kill some broadleaf species. It should be applied at a rate of 1 quart/100 gallons. Haggar and Elliot (1978) suggest biennial application of Dalapon® to control Holcus lanatus. Dalapon® is cleared for use on rights-of-way and for spot treatment of grazed areas. It is lethal to 50% of tested animals (LD50) at 9330 mg/kg of body weight but is classified as being of "relatively no hazard." The herbicide will persist in the soil for up to 8 weeks.
There are several petroleum oils used for weed control. The herbicidal use of oils depends on their chemical and physical properties. Most contact oils evaporate slowly and owe their plant toxicity to their high content of aromatic compounds. Spraying oil on Holcus lanatus will be effective only if the entire plant is coated.
Herbicides can be applied uniformly over an area of large infestations or by spot spraying individual plants. Dr. McHenry recommends using a flat-fan nozzle (Spraying Systems Co. #8003 or #8004 nozzle tip), rather than the cone nozzles available on most garden sprayers. Cone sprayers produce greater atomization of the chemicals and increase the chance of drift into unwanted areas. Spraying should be done on calm days to dry plants, as dew or rain will tend to dilute the herbicide reducing its effectiveness. When spraying large areas, a horizontal boom (6-8 feet long) made from aluminum tubing will improve herbicide coverage.
Holcus lanatus is present on the Northern California Coast Range Preserve (NCCRP). It is not a major problem species but is present along roads in wet portions of several of the meadows. Hand pulling of the plants and removal of the flowering heads has decreased the size of some of the infestations. Prescribed burning has not been used due to potential fire control problems.
Contact: Peter Steel, Caretaker NCCRP 42101 Wilderness Lodge Road Branscomb, CA 95417 (707) 984-6653
Monitoring is needed to determine the effectiveness of any velvet grass control measures. These will vary depending upon the degree of the problem on a given preserve.
Monitoring programs are ongoing at the following Oregon TNC preserves: Willow Creek, Cascade Head, Wren Prairie, and Camassia Plateau. For further information, contact:
Cathy Macdonald, Land Steward The Nature Conservancy Oregon Field Office 1205 25th Avenue Portland, OR 97210 (503) 228-9561
Management Research Needs:
Much additional research is needed on obligate parasites and pathogens of Holcus lanatus before any viable biocontrol measures can be developed. Prescribed burning is a relatively effective control technique in Europe, but more information should be obtained on its use as a control method.
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