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Physical and Cultural Control
There are some effective non-chemical methods for controlling A. fatua. These are mainly soil cultivation and crop rotation. The most effective non-chemical control was achieved by the shallowest cultivation possible, carried out as late as possible (Zorner et al., 1984). Tine cultivation, besides favouring increase of an uncontrolled population, results in a faster population decline than ploughing (Wilson and Cussans, 1983).
Depth of burial and crop rotation influence the seed bank (Froud-Williams, 1987). Peters (1991) found no viable seeds after 3 years of intensive soil tillage. Under zero tillage the numbers of A. fatua are generally reduced, but the control of surviving plants with herbicides can be less effective (Bowren, 1983). Summer treatment of soil after cereal harvest (stubble ploughing, summer deep tillage and spring seed-bed preparation), which buries A. fatua seeds, can create good conditions for weed seed germination and help to markedly reduce weed seed banks (Demo, 1999). Palys et al. (1999) reported that direct sowing and no ploughing caused the greatest increases in the densities of A. fatua in a faba bean/winter wheat/spring barley rotation prior to harvest. Post-harvest soil cultivation can promote weed seed germination and emerged weeds can be controlled with glyphosate prior to drilling. This treatment combined with a pre- or post-emergence herbicide programme resulted in reduced numbers and a decline in A. fatua over a 4-year period (Hutcheon et al., 1998).
Straw burning kills many seeds and reduces the dormancy of survivors (Ivens, 1978; Moss, 1985). In contrast, stubble cultivations have a smaller effect on the germination of A. fatua (Cussans et al., 1987). Delayed sowing results in a consistently high degree of A. fatua control but can also result in significant losses in grain yield and quality (Hunter, 1983).
In many cases farmers have had to seek alternative methods in their control of A. fatua. In a study on the LIFE pilot farm in the UK, the presence of the wild oats in such abundance caused a switch to spring cropping of oilseed rape and peas in addition to a ley period of 1 year grass-clover mix (Davies et al., 1997). In cereal crops, reducing the seed bank of weed seeds is the optimum control method. This can be done through changes in the crop sequences (Malik et al., 1996).
Schoofs and Entz (2000) reported forage systems (e.g. triticale) were at least as effective as the sprayed wheat control in suppressing wild oat.
In contrast to these indirect control methods there are only a few non-chemical measures for direct control of A. fatua. Mechanical methods are mostly less successful because of the large seed and dense root system (Koch and Hurle, 1978). Nevertheless, harrowing or hoeing may break dormancy and therefore increase late emergence (Raju et al., 1988). A. fatua and other grasses are not susceptible to thermal control methods (Ascard, 1995). However, a flame weeder used in an onion crop resulted in 31-93% control of A. fatua (Mojzis, 2002). Tsuruuchi (1986) reported that emergence of A. fatua in wheat and barley can be reduced by flooding. Soil solarization is used in Israel, the USA, Italy and India (Arora and Yaduraju, 1998) to control A. fatua as well as other weeds and pests (Cartia, 1985).
Composting has been found to kill weed seeds (Tompkins et al., 1998). In an experiment conducted using feedlot manure containing 12 weed species of which A. fatua was one, composting reduced the viability drastically within two weeks and killed all seeds within four weeks (Tompkins et al., 1998).
Olson et al. (1999) found that shoot extracts and living tissue extracts from wheat (Triticum aestivum) resulted in a significant decrease in total biomass, pigment, carbohydrate and protein content of A. fatua. In a field trial in Pakistan, sorghum water extract reduced the density and biomass of A. fatua by 22-27% (Cheema et al., 2002). Parthenin, a natural extract from Parthenuim hysterophorus reduced germination of A. fatua and inhibited shoot and root growth (Batish et al., 2002). In a study on the allelopathic effects of Triticum speltoides (a wild relative of wheat), one out of 17 accessions were found to reduce the radicle length of A. fatua by 50% (Hashem and Adkins, 1998).
Enhanced crop competition can also reduce the growth and yield reduction effect of A. fatua. Increasing the sowing rate of five varieties of barley improved the competitiveness of all varieties as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields (O'Donovan et al., 2000a). In field trials in Canada, hybrid rape varieties were twice as competitive against A. fatua as open-pollinated varieties (Zand and Beckie, 2002). Xue and Stougaard (2002) showed that the combined effects of large seed size and increased wheat sowing rate could decrease A. fatua biomass and seed production by 20%.
A commercially available smoke-water solution has also been shown to stimulate the germination of A. fatua (Adkins and Peters, 2001).
Few papers have been published concerning biological approaches for controlling A. fatua. They are resultant of fungal infections such as those by Erysiphe graminis f.sp. avenae (Sabri and Clark, 1996; Sabri et al., 1997), Puccinia coronata (Chong and Seaman, 1996, 1997; Salmeron-Zamora et al., 1996; Johnston et al., 2000), P. coronata f.sp. avenae (Carsten et al., 2000), P. graminis (Harder and Anema, 1993), P. recondita (Pfleeger et al., 1999), Pyrenophora (Kastanias and Chrysayi Tokousbalides, 2000), nematodes (Riley and McKay, 1991) or hydroxamic acids that have allelopathic effects (Perez, 1990). A. fatua is generally susceptible to the same range of parasites as cultivated oats (Sharma and van den Born, 1978). Research into fungal pathogens for the biological control of A. fatua is occurring in many countries including Vietnam (Hetherington et al., 1996), Australia, USA, Netherlands, Japan and South Africa (McRae, 1998).
A. fatua has been confirmed, via virological analysis, to be a natural host plant for the Oat blue dwarf virus (Vacke, 1998). The majority of host plants identified in this study exhibited characteristic symptoms of the infection. Another pathogen, Drechslera avenacea, was identified and isolated and found to be specific to A. fatua over wheat (Zhang and Li, 1996) and has been investigated as a potential bioherbicidal organism for A. fatua (Hetherington et al., 2002). Chong and Seaman (1997) isolated 101 virulence phenotypes from 189 isolates from A. fatua and commercial field oats in Manitoba and Ontario, Canada. Hot dry weather was seen to slow the infection of the fungus.
The effect of Erysiphe graminis f.sp. avenae on the photosynthesis and respiration of A. fatua was studied by Sabri et al. (1997). It was evident from these studies that E. graminis [Blumeria graminis] reduced levels of photosynthesis and chlorophyll. In a comparison of wild oats with cultivated crops in their tolerance to B. graminis it was seen that the wild oats were significantly more tolerant, due to the lower sensitivity of their metabolism to B. graminis (Sabri and Clarke, 1996).
The ant species Messor barbarus has been shown to preferentially predate A. fatua seeds (Detrain and Pasteels, 2000).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
A. fatua is considered to be among the world's worst agricultural weeds and is still increasing in importance (Holm et al., 1977; van der Puy, 1986). Daugovish et al. (2003) estimated that A. fatua infests 11 million ha of cropland in the US. Mortimer (1985) called A. fatua an intractable weed, because its life cycle is synchronized with the growth of the crop. A computer package has been developed for assessing the economics of A. fatua control in cereal and oilseed crops (O'Donovan, 1996).
A. fatua shows a high competitive ability and is often more competitive than Alopecurus myosuroides (Farahbakhsh et al., 1987), Galium aparine (Wilson and Wright, 1990) or wheat (Martin and Field, 1988). Shoot biomass and competitiveness are enhanced by ploughing and high levels of fertilization with nitrogen (Bozic, 1986) and phosphorus (Konesky et al., 1989). Competition between cereals and A. fatua occurs predominantly below ground (Satorre and Snaydon, 1992). Crop yield response depends on time of emergence and density (Farahbakhsh and Murphy, 1986). In cereals, competition starts mainly at the two-node stage and reduces the number of crop tillers (Morishita and Thill, 1988). However, a study by Dhaliwal (1998) found that when mixed with A. fatua, all barley cultivars being tested displayed improved growth characteristics. O'Donovan et al. (1999b) also found that each year wild oat seed yield and shoot dry weight decreased as barley plant density increased.
Many damage threshold levels have been estimated for various crops. For cereals the following have been reported: eight A. fatua plants/m² caused 14% yield reduction and 5.5% less protein content in wheat (Wimschneider et al., 1990); 100 panicles/m² reduced the yield of winter wheat by 34% and of spring wheat by 40% (Rola, 1987); 60 plants/m² caused an average yield loss of 0.5 t/ha in about 100 wheat trials (Meinert, 1983); wheat yield loss was below 1% up to 3 plants of A. fatua/m², reached 2.2% at 5 plants and was 50-60% at 100 plants (Walia et al., 1998); infestations ranging from 8 to 662 seedlings/m² in the spring resulted in yield reductions varying from 0 to 72% in spring barley (Wilson and Peters, 1982; Weaver and Ivany, 1998); 10 culms diminished spring barley yield by 0.08-0.15 t/ha (Korolova et al., 2000); 17-30% reduction in winter wheat yields was caused by 8-16 A. fatua plants/m², although with fewer than 8 plants/m² yield reductions were not significant (Pardo and Encina, 1977); 1% yield loss was measured in cereals for each A. fatua plant/m² (Wilson and Wright, 1990); the damage threshold in spring barley is around 10 A. fatua plants/m² (Murdoch et al., 1988); no yield loss was observed with 4 A. fatua plants/m² in wheat and with 15 plants/m² in cultivated oats (Mondragon et al., 1989). In contrast to the majority of reports, Kiec (1997) found that planting densities of 0, 4, 8, 16 and 32 pcs/m² in crops of spring wheat had no effect on crop yield or other triticale variables. In the case of sugarbeet, Mesbah et al. (1995) found that one A. fatua plant/m of row reduced yield by 14%, but in mixed density with 0.8 Sinapis arvensis, yield (plants/m of row) was reduced by 29%. For maize, 9 or 27 A. fatua plants/m of row reduced maize grain yield by 14 or 25%, respectively, whereas 3 plants/m of row caused no significant yield reduction (Castillo and Ahrens, 1986). In field trials using peas, A. fatua was shown to cause significant reductions in total yield and also a reduction in seeds per pod (Wright and Baloch, 1999).
Variations in the yield reduction potential of A. fatua as evidenced above are inevitable and are the result of site to site, climatic and genetic variation. An analysis of the economic benefits of integrated weed management approaches for the control of A. fatua in northern New South Wales, Australia, reinforced the idea that strategies that directly reduce seed production and seed bank populations yield the greatest economic benefit (Jones and Medd, 1997). Crop competition and bioeconomic decision support models have been developed for A. fatua control. A decision model of Cousens et al. (1986) predicts that the highest long-term benefits will be obtained when A. fatua is controlled at a density of 2-3 seedlings/m². Jones and Medd (2000) convincingly identify the shortcomings of A. fatua control strategies that simply attempt to minimise yield impacts in a single year and advocate population based management that attempts to reduce the soil seed bank over a longer term.
The continuous and widespread use of herbicides for the control of A. fatua has frequently resulted in the evolution of herbicide resistance and A. fatua is listed as the second most herbicide resistance prone weed in the world (Heap, 2003). Herbicide resistant populations of A. fatua have been reported in Australia, Canada, Belgium, Chile, France, South Africa, the UK and USA (Heap, 2003) and resistance to at least five herbicide modes of action has been documented. In Canada, where the problem is most severe, upwards of 2 million acres of cropland are infested with herbicide resistant A. fatua. In a recent survey in Saskatchewan, Canada, over one half of fields had populations of A. fatua resistant to either ACC'ase or ALS-inhibiting herbicides (Beckie et al., 2002).
Only a few data are available concerning the long-term effect of A. fatua as a host for cereal pests and diseases. Rauber (1977) and Sharma and van den Born (1978) found no obvious differences in susceptibility between A. fatua and A. sativa. Nevertheless, Madariaga and Scharen (1985) reported that Septoria tritici [Mycosphaerella graminicola] on A. fatua was not pathogenic to wheat. In a study by Barlow et al. (1999) results indicated that A. fatua was a poor host for the tarnished plant bug (Lygus hesperus).