Incidence of grassweeds is largely confined to the major cereal growing regions of the country. Wild oats (Avena spp.) are distributed from Yorkshire to Devon, and the intense arable areas of south and east Scotland.
Identification and Biology
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 (wild-oat)the florets fall as single seeds, whereas in A. sterilis (winter wild-oat) 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. sterilis it is 35-60 mm and inserted below midway on the lemma.
Biology – Wild oats are one of the most aggressive arable weeds and have been encouraged by the increasing dominance of autumn cropping. Only 5 plants/m2 are required to produce a 5% loss in yield.
Avena sterilis 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..
Products to control wild oats