**Avena barbata Brot. (Poaceae)**

**Slender wild oat**

**Description**. Annual, 3-6 (8) dm tall, erect, stems erect, glabrous
to short-soft-hairy. Leaves alternate; ligules 1-4 mm long, lacerate,
auricles absent; sheaths glabrous to pubescent; blades linear, flat, 1-5
mm wide, glabrous to soft-puberulent. Inflorescence an open terminal
panicle, 3-10 cm long. Spikelets 20-30 mm long, slightly compressed,
composed of 3-8 florets, the glumes linear to narrowly lanceolate, the
lower one 5-10 mm long, 1-nerved, the upper one 8-13 mm long, 3-nerved;
lemmas 12-17 mm long, lanceolate, 3-5-nerved, the back keeled to
rounded, the apex with two lateral teeth 4-5 mm long, the back of the
lemma with a bent awn l2-20 mm long. In California, flowering from March
to June. (Arnow 1987, Hitchcock 1944, Holmgren and Holmgren 1977, Munz
1959, Rocha Afonso 1980, Wilken 1993).

**Note**: Originally believed derived from *A. fatua, A. harbata* most
likely arose independently as a polyploid derivative of two other
species, *Avena hirtula* and *Avena wiestii* (Alicchio et al. 1995*,*
Garcia et al. 1991, Katsiotis 1997, Ladizinksky *1995). Avena fatua,* a
close relative of A. *sativa* (cultivated oat), may have evolved in
response to early cultivation, first as a crop, and later coincident
with cereal production (Hjelmquist 1955, Lindsay 1956*,* Sexsmith 1967).
Darmency and Aujas (1992) found genetic variation for growth rates and
competitive ability in *A. fatua.*

**Geographic distribution**. A native of Europe, slender wild oat has
been introduced into western North America, southern Africa, and South
America (Arnold and de Wet 1993, Arnow 1987, Gibbs Russell et al.
1955*,* Holmgren and Holmgren 1977, Montenegro et al. 1991, Munz 1959,
Romero Zarco 1996). However, the related Eurasian *A. fatua,* has been
introduced and has become naturalized , in addition to the above, in
Australia, New Zealand, Hawaii and Japan (Chapman 1991, Holm et al.
1977, Ohwi 1965, Wagner et al. 1990, Webb et al. 1988).

*Avena barbata* was first reported from California by Vasey (1885),
although it probably had become widespread much earlier (Robbins 1940).
*Avena barbata* was probably introduced into California more than once
during the 18th century. However, recent studies suggest that nearly all
naturalized California strains are most closely related to those found
in southwestern Spain (de la Vega 1991, Garcia et al. 1989). Cluster and
Allard (1995) and Rai (1985) also provided evidence showing that
significant ecotypic differentiation may have taken place in California
within the last 150-200 generations (perhaps less than 150-200 years).
*Avena fatua* also was well established before the end of the 18th
century (Hendry and Bellue 1925, Robbins 1940).

Both species have been reported from all northern California Channel
Islands and Santa Barbara Island (Junak et al. 1997) and are widespread
in most California counties west of the Great Basin and deserts
(Anonymous 1998, Wilken 1993).

**Reproductive and vegetative biology**. Both *Avena barbata* and *A.
fatua* are self-compatible and strongly selfing (Clegg and Allard 1972,
Imam and Allard 1965), despite their dependency on wind-pollination.
Populations in California show considerable ecological differentiation
with respect to allozymes (Hamrick and Allard 1972). Both *Avena
barbata* and *A. fatua* are characterized by considerable genetic
variation (e.g., Jain 1969, Jain and Marshall 1970, Jain and Rai 1974,
Jain et al. 1981, Marshall and Jain 1969), including such traits as
growth rates, seed dormancy, and germination responses (Somersalo et al.
1988, Thurston 1963). *Avena fatua* shows a broad range of response to
regional climates, including the ability to flower and produce seeds at
any time of the year in subtropical climates (Jain 1969, Thurston 1959,
1963). Persistence in cultivated fields may also depend on variation in
seed dormancy and germiantion responses (Banting 1996).

Seeds of A. *fatua* generally germinate in the late fall and early
winter, depending on soil moisture, in warm and cool temperate climates
(Fernandez-Quinantilla et al. 1990). Germination rates of fresh seeds
can exceed 50% under most temperate conditions, leading to immediate
recruitment following the first seasonal rains (Fernandez-Quinantilla et
al. 1990, Thurston 1962). However, seeds can remain dormant or undergo
secondary dormancy, especially under cold conditions (Fregeau and
Burrows 1989, Sawhney 1989). Dormancy is generally broken by a
combination of moisture and relatively warm (20˚ to 40˚ C) soil
conditions (Foley 1994). Although seeds buried as deep as 20 cm can
germinate and produce viable seedlings, buried seeds may remain dormant
from 4 to 7 years, unless exposed by deep cultivation and short-days,
followed by relatively warm, moist conditions (Conn 1990, Hilton 1985,
Hilton and Bitterli 1983, Johnston et al. 1994, Miller and Nalewaja
1990, Thurston 1961, 1962).

Plants grow relatively rapidly in Europe, with flowering and fruiting
dependent on soil nutrients, density of associated species, and the
extent of spring rains (Cousens et al. 1992). In California oak
*(Quercus agrifolia)* savanna, *Avena fatua* is generally restricted to
open sunny sites, displaying reduced growth and lower competitive
ability under shade (Maranon and Bartolome 1993). Hobbs (1986) provided
evidence that over the long-term, *Avena* and other annual grassland
species are slowly replaced by coastal sage scrub under some conditions.
Although plants of *A. barbata* show reduced fruit production under
drought conditions, the mean fruit weight remained relatively uniform
(Ewing and Menke 1983a, 1983b). In California, natural populations of
*Avena fatua* can have strong allelopathic effects (Tinnin and Muller
1971a, 1971b). Under experimental conditions, root exudates of A.
*fatua* are allelopathic to several different crop seeds (Perez and
Ormeno-Nunez 1991).

**Ecological distribution**. Both *Avena barbata* and *A. fatua* occur
in dry cultivated fields, roadsides, waste places, formerly tilled
fields, and grazed pastures, although the latter species tends to be
restricted to disturbed or formerly tilled sites (Arnow 1987, Baum et
al. 1972, Holmgren and Holmgren 1977, Munz 1959, Rocha Afonso 1980,
Wilken 1993, Stromberg and Griffin 1996)

**Weed status**. *Avena barbata* is not considered a noxious weed in
agricultural or horticultural practice, at least at a global level (not
listed by Holm et al. 1977), nor is it considered a noxious weed by the
State Dept. of Food and Agriculture (Anonymous 1996). It is not listed
for the United States in Lorenzi and Jeffery (1987). In contrast, *A.
fatua* is one of the most widespread and serious weeds of the world,
primarily in cultivated cereal crops (Holm et al.1977, Lindsay 1956,
Lorenzi and Jeffery 1987), probably as a result of its widespread
cultivation for grain and later as a hay crop for over 2,000 years
(Hjelmquist 1955, Jessen and Helbaek 1945, Coffman 1961).

**Microbial pathogens**. *Avena* species can serve as hosts to dwarf
mosaic viruses, but infections in *Avena fatua* and *A. sativa* were not
found to be virulent (Achon et al. 1996). Smut and mildew fungi
*(Ustilago aveneae, Erysiphe graminis)* have been reported from *Avena
barbata* and *A. fatua* (Nielsen 1993, Sabri et al. 1997, Sabri and
Clarke 1996). *Avena barbata* includes strains both susceptible and
resistant to infection by *Puccinia* rust fungi (Karow et al. 1997,
Katsiotis and Forsberg 1995). Both *Avena fatua* and *A. sativa* are
hosts to *Puccinia coronata* and *P. graminis,* which often cause
significant damage to plants under cultivation in Canada (Chong 1988,
1990, Chuang and Harder 1991, Chong and Seaman 1989, 1990, Harder 1989,
Harder and Dale 1990, Kolmer and Chong 1993). Douglas et al. (1996,
1997) summarized and evaluated a program that used *Puccinia coronata*
as a biocontrol of *Avena barbata* on San Clemente Island.

*Avena barbata* growth may be enhanced by mycorrhizal infection (Rillig
et al. 1998). Infection by mycorrhizal fungi *(Glomus etunicatum, G.
intraradices)* enhanced growth of *Avena fatua* in cultivated fields of
*Avena sativa.* (Koide et al. 1988, Koide and Lu 1992, Lu and Koide
1991).

**Insect pathogens**. No literature was found that reported insects
detrimental to *Avena barbata* or *A. fatua,* although the latter has
been reported as a incidental host to Mirid bugs *(Calocoris
norvegicus)* infesting pistacios (Purcell and Welter 1990).

**Herbicide control**. Price et al. (1988) described the use of barban
and difenzoquat in controlling *Avena barbata..* Numerous studies have
evaluated the use of several herbicides in controlling *A. fatua,*
including chlorsulfuron, diclofop-methyl, dipenzoquat, flamprop-methyl,
fluazifop, glyphosate, haloxyfop, metribuzin, quizalofop, sethoxydim,
2,4-D, and triallate (Chow 1988, Donald 1990, Eberlein et al. 1988,
Friesen 1988, Harker and O\'Sullivan 1988, Jam and van den Born 1989,
Kafiz et al. 1989, Kirkland et al.1989, Kudsk 1988, Martin et al. 1989,
Miller 1990, Morrison 1990, Thai et al. 1989, Warkintin et al. 1988).
Nietschke (1996) and Nietschke and Medd (1996) provided general reviews
on control of*Avena fatua* in cultivated crops.

Combinations of flurtamone and ethalfiuralin was shown to be more
effective against *A. fatua* than either alone (Blackshaw et al. 1992).
Harker et al (1995) reported successful treatment of *Avena fatua* with
ethametsulfuron when mixed with sethoxydim, but other combinations (with
haloxyfop, fluazifop, and quizalofop) caused significant injury to the
associated dicot crop (canola). Wall (1994) found mixtures of fluazifop
and clethodim effective in controlling annual grasses, including
*Avena,* in flax fields. Wells (1989) reported enhanced effect of
glyphosate treatments using adjuvants in control of *Avena fatua..*
Grayson et al. (1995) and Murphy et al. (1995) reported similar results
with flamprop-m-isopropyl. Ammonium sulfate increased the efficacy of
sethoxydim in experimental plants of *Avena fatua* (Smith and Vanden
Born 1992). Ahrens and Ehr (1991) reported enhanced efficacy of
atrazine-cyanazine mixtures when plants of *Avena fatua* were treated
with tridiphane. Sodium bisulfate enhanced the effect of imazamethabenz
in controlling *Avena fatua* (Liu et al 1995). Xie et al. (1994, 1997)
reported effective control of *Avena fatua* using mixtures of
imazamethabenz and fenoxaprop under drought conditions.

In contrast, Jensen and Caseley (1990) reported antagonistic effects of
2,4-D amine and bentazone with tralkoxydim in attempts to control *Avena
fatua.* Eberlein, et al. (1988) studied anatgonistic combinations of
herbicides, showing that, in some cases, thiameturon interfered
significantly with diclofop control of *Avena* *fatua.*

Strains of *Avena fatua* resistant to atrazine, diclofop, triallate,
cyclohexanedione, and aryloxyphenoxypropionate have been reported by
Powles and Stewart (1990), Devine et al. (1992), Joseph et al. (1990),
Morrison and Devine (1995), and Seefeldt et al. 1994). Kibite et al.
(1995) studied inheritance of genes conferring resistance to diclofop
and fenoxaprop -p-ethyl in *Avena sativa* x *A. fatua* hybrids. However,
strains resistant to triallate were susceptible to and could be
controlled by atrazine, ethalfiuralin, fenoxaprop-P, flamprop,
imazamethabenz, and tralkoxydim (Blackshaw et al. 1996). Thill et al.
(1994) evaluated and discussed Integrated weed management strategies for
delaying the evolution of herbicide resistance in *Avena fatua.*

**Other control methods**. The use of organic mulches enhanced the
competitive ability of outplanted *Artemisia californica* over *Avena
fatua* in potential coastal sage scrub communities (Zink and Allen
1998).

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