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CDFA Plant Health

Noxious Weed Photographic Gallery

Punagrass [Stipa brachycaetum Godron][Bayer code: none] [CDFA list: A] Photographs Map of Distribution


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[SYNONYMS] [GENERAL DESCRIPTION] [SEEDLINGS] [MATURE PLANT] [ROOTS and UNDERGROUND STRUCTURES] [SPIKELETS/FLORETS] [HABITAT] [DISTRIBUTION] [PROPAGATION/PHENOLOGY] [MANAGEMENT FAVORING/DISCOURAGING SURVIVAL] [SIMILAR SPECIES] [CONTROL METHODS]


SYNONYMS: Achnatherum brachychaetum (Godron) Barkworth

GENERAL DESCRIPTION: Densely tufted perennial, with shallow roots and erect stems to 1 m tall. Foliage is tough, unpalatable to livestock, and present nearly year round. Punagrass is often associated with alfalfa fields. The dense clumps can mechanically interfere with mowing. Because it grows faster than alfalfa, infestations are easier to detect 1 to 2 weeks after cutting. Introduced from Argentina. There are other Achnatherum species in South America that closely resemble punagrass and have not been studied in detail. At publication time, the relationships of these species and correct scientific name of California plants are questionable.

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SEEDLINGS: No information available.

MATURE PLANT: Tufted. Blades linear, 1-2 mm wide, 40-60 cm long, flat or slightly rolled upward (involute), and rigid. Sheaths open, glabrous, but with ciliate hairs along the upper margins and especially at the position of the auricles. Ligules membranous.

ROOTS and UNDERGROUND STRUCTURES: Roots fibrous, shallow.

SPIKELETS/FLORETS: Spring. Panicles nearly pyramidal or with ascending branches, 20-30 cm long, lax, barely exceeding the tops of the blades. Spikelets with 1 floret. Glumes glabrous, nearly equal, 6-8 mm long. Lemmas stiff to hard, sparsely covered with very short hairs (< 0.5 mm long), and tightly enfolding palea and caryopsis. Lemma tips with hairs 0.8-2 mm long and 1 awn. Awns 15-20 mm long, bent twice, with very short rough hairs (scabrous) along the basal segment. The distal awn segment is typically straight at maturity. Paleas thick, stiff, with conspicuous veins, and at least ¾ of the length of the lemmas. Florets disperse as units when the axis (rachilla) breaks above glumes. Florets 4.5-6 mm long, cylindrical, and blunt at the base (callous). In addition, small cleistogamous seeds (from self-fertilization) develop within the basal leaf sheaths. Cleistogamous spikelets have papery glumes, lemmas, and paleas enclosing the caryopses (grains or 1-seeded fruits of grasses). Glumes about 5 mm long, long-pointed or with an awn 2 mm long or less. Caryopses variable, +/- ovate, slightly compressed, gray-, reddish-, or yellowish-brown, smooth, hard, and about 3 mm long. Cleistogamous seeds appear to remain within the leaf sheaths until disturbed or senesced culms fall to the ground.

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HABITAT: Disturbed sites. Often associated with alfalfa fields and nearby drainage ditches, dairies, and horse pastures.

DISTRIBUTION: San Francisco Bay region (s Contra Costa, n Alameda cos.), southwestern South Coast Ranges (sc Santa Barbara Co.), southwestern Transverse Ranges and northern South Coast (s Ventura Co.). Previous infestations now eradicated in central San Joaquin Valley (c Fresno Co.) To 300 m (1000 ft).

PROPAGATION/PHENOLOGY: Reproduces by seed. Cleistogamous seed develops within the leaf sheaths at the bases of plants in early summer and matures by late summer. Cleistogamous seed is hard-coated and can persist in the soil for at least 2 years.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Cultivation discourages survival, especially of seedlings.

SIMILAR SPECIES: Several native needlegrass (Achnatherum, Nassella) species resemble punagrass. However, native needlegrasses do not produce cleistogamous seed within the leaf sheaths at the bases of plants. In addition, native needlegrasses are not weedy and are unlikely to inhabit disturbed sites such as agricultural fields and dairies.

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CONTROL METHODS:

Prevention: Punagrass is a shallow rooted perennial bunchgrass found primarily in alfalfa fields or along irrigation ditches. It is native to Argentina, where it is a serious problem in alfalfa. It is believed to have arrived in contaminated alfalfa seed. Therefore, prevent new infestations by planting only certified alfalfa seed. If it is economically feasible, shift crop rotations to other annual or perennial crops where tillage can be utilized for weed management.

Mechanical: Punagrass may vegetatively reproduce from the crown, but is not stoloniferous or rhizomatous. It also has the ability to produce seed cleistogamously (seed produced from self fertilized flowers in the base of the leaf sheaths). Cleistogamous seed production has allowed punagrass to persist in alfalfa fields that are cut every month. Frequent mowing can eliminate aerial seed production. However, vegetative regrowth will rapidly occur, and viable, cleistogamous seed will be produced. Mature punagrass clumps are very rigid, but may be pulled or dug. Clumps should be removed, dried, and possibly burned. Tillage is an effective control method, especially when punagrass is in the seedling stage. Repeated cultivations will also eliminate established clumps. Infested areas should be monitored for at least two years since seed are viable for that length of time.

Biological: There are no biocontrol agents for punagrass, and there is little information regarding any plant/insect interactions. The primary objective should be punagrass eradication. Livestock in Argentina will generally graze around infestations and will graze punagrass if it is the only forage source.

Chemical: Recent research has examined several herbicides for punagrass control. In alfalfa, fall applications of either sethoxydim (0.45 lb ai/A) or clethodim (0.25 lb ai/A) provided 70-80% control, 8 months after treatment. Fall applications (late October) were more effective than spring (early March) applications. Applications in both the fall and spring resulted in 95% punagrass control, 8 months after treatment. A fall tank mix application of sethoxydim (0.45 lb ai/A) and thiazopyr (0.50 lb ai/A) also provided 95% control. Pronamide (2.0 lb ai/A) did not control punagrass. Fall applications of glyphosate (2% v/v) to individual plants resulted in excellent control (99%), eight months after treatment. However, alfalfa plants surrounding the punagrass clumps were also killed. Therefore, glyphosate may be an excellent spot application treatment for punagrass along irrigation ditches or non-crop areas. Any infested site should be monitored for regrowth and new seedling recruitment following treatment. Regrowth from treated clumps has been observed with most herbicide treatments. Larger clumps will be more tolerant than seedlings or small clumps.

Integrated Management: Crop rotation that allows the use of both tillage and selective grass herbicides is the best approach for eradicating punagrass. Infested areas should be monitored for several years and new seedlings should be aggressively managed to prevent new clumps from forming.

References
1972. Puna Grass. Sacramento: CDFA, Division of Plant Industry, Exclusion and Detection Manual.
Ares, J. O. 1972. The reproductive characteristics of Stipa brachychaeta and their importance in colonization. Malezas y su control 1:15
Eilberg, BA de and Soriano, A. 1-1972. Dormancy and germination of disseminules of Stipa brachychaeta buried in soil and undergoing periodic depth changes. Malezas y su control 1:64-75.
Morris, D. I. 1983. Stipa brachychaeta, a weed new to Tasmania. Australian Weeds. 2:172-
Santis, L. de, Loiacono-de, Silva MS, De-Silva, MS Loiacono, and Silva-MS, Loiaono de. 1983. Insects that destroy 'espartillo' (Stipa brachychaeta) and their parasites. Contributions of the American Entomological Institute 20:402-427.
Verdejo, J., Etiennot, A., Quiroga, R., Maluf, E. J., and Schell, J. 11-1983. Trial with pre-sowing and pre-emergence herbicides for control of Stipa brachychaeta Godr. Malezas 11:261-263.

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3/18/15