Wild Oats

Identification - Seedlings have an anti-clockwise twist, hairs on the leaf margins, a membranous ligule and no auricles. Mature plants grow up to 150 cm tall. The stem is round, the leaves are hairy. There are no auricles, and the ligule is tall and rounded. The seed head is an open panicle, and the spikelets usually contain 2-3 florets. The panicle may contain up to 250 awned seeds, which range in colour all the way from black to white. In Avena fatua the florets fall as single seeds, whereas in A. ludoviciana the seeds fall as a united floret. The awn of A. fatua is 25-40 mm long and inserted about half way up the lemma. In A. ludoviciana it is 35-60 mm and inserted below midway on the lemma.

Biology - Wild oats are one of the most aggressive arable weeds and has been encouraged by the increasing dominance of autumn cropping. Only 5 plants/m2 are required to produce a 5% loss in yield.
Avena ludoviciana is mainly autumn germinating, while A. fatua is both spring and autumn germinating.

Seedling emergence is dependant on soil moisture and temperature but is also affected by soil cultivation and seed dormancy. Germination flushes occur in the autumn and again in the spring at temperatures in the range of 10-26°C.  Deep burial of the seed by ploughing induces dormancy. Seeds can remain viable for up to 13 years, but few remain viable for more than 3 years. The seedbank half-life is about 6 months.  At weed densities up to 40 plants/m2 each plant can produce about 225 seeds, but at densities over 50/m2 this can fall to below 50. The net result is that in crops which are untreated, seed production can range from 1,000 to 10,000/m².

 Ryegrasses

Italian ryegrass Identification - Leaves hairless with glossy underside, and tend to be wider than perennial ryegrass. When the stem is cut horizontally the leaves can be seen to be rolled in the sheath. The stems are round (perennial ryegrass is flattened) and auricles are present and without hairs (wheat auricles tend to have hairs). The seedhead is a flattened spike with spikelets arranged alternately on opposite sides of the stem. The spikelets are awned and stalkless and have their rounded face next to the stem. (The spikes of couch are similar but have the flattened face of the spikelets next to the stem.)

Perennial Ryegrass Identification - Leaves hairless with glossy underside, and tend to be narrower than Italian ryegrass. When the stem is cut horizontally the leaves can be seen to be folded in the sheath. The stems are flattened (Italian ryegrass rounded). Auricles are present and hairless. The seedhead looks like Italian ryegrass except that there are no awns on the spikelets.

Biology - Ryegrasses have a competitive index of 0.85, compared with 1.0 for wild oats and 0.4 for blackgrass, so even moderate populations can have severe effects on crop yield.  Flowering time is much more variable and later types may not have shed before harvest. Seed can become dormant in the soil and persist for two years and exceptionally for four years.

Italian ryegrass can be annual or biennial, 30-90 cm high. It can be very well tillered or not depending on crop competition, but is very aggressive in its spring growth pattern. Flowering occurs in May-August and seed is shed before harvest and can persist in the soil for up to seven years.

Perennial ryegrass is a competitive weed, but less so than Italian ryegrass. As the name indicates it is a perennial plant 30-60 cm tall and will tiller as much as conditions allow.

 Brome Species

Identification - Although it is relatively easy to distinguish bromes from other grass weeds, identifying individual brome species is difficult, particularly in the vegetative stage. Bromes have a rounded stem and hairy leaves and there are no auricles. The ligule in sterile brome is 2-4 mm long and toothed, in great brome it is 2-6 mm long, rounded and jagged.  In meadow brome it is 1-4mm long, flat, and toothed; In soft brome it is short –up to 2.5 mm, rounded and jagged, while in rye brome it is only 1-2 mm, flat and toothed.

Biology - Brome species are most commonly confined to headlands or to patches within fields. Their relative competitiveness is roughly equal to ryegrass, slightly less than wild oats, but twice as competitive as blackgrass on a plant for plant basis.

Anisantha bromes (sterile, great brome) germinat in the autumn and require vernalisation to flower. They germinate in the dark, and exposure to light induces dormancy. Seed can remain viable for 2 years, so if ploughing brings old seed to the surface it can become a problem in the following crop.

Serrafalcus bromes (meadow, soft, and rye brome) differ in that the seed needs light and also a period of maturation to germinate. For this reason cultivations after harvest should be delayed for a month to prevent inducing dormancy, after which seeds can remain viable for 7-10 years.