Italian rye-grass

Identification

Italian rye-grass can be distinguished from perennial rye-grass by two characteristics:

• Leaves are rolled in the shoot in Italian rye-grass but folded in the shoots of perennial rye-grass
• Spikelets of Italian rye-grass have awns whereas those of perennial rye-grass are awnless.

Damage

Rye-grass is more competitive than black-grass and 5 plants/m² typically causes a yield loss of 5% in cereals, but crop losses of up to 89% have been recorded at high infestations. Rye-grass also tillers more profusely than black-grass; each plant commonly producing over 20 heads and 5,000 seeds. As a result populations can build up very rapidly.

Management Options

Rye-grass has a very similar biology to black-grass in terms of emergence patterns, seed persistence and depth of emergence, so the non-chemical methods of control used against that weed are also appropriate for rye-grass.

Many farmers and agronomists believe that there is greater spring emergence with rye-grass than with black-grass and, as a consequence, herbicides tended to be applied in spring against rye-grass. Recent Rothamsted studies do not support this belief - monitoring studies on many fields showed that the majority (94%) of Italian rye-grass plants in winter wheat fields emerge between October and December, with only 6% emerging in spring. Autumn emerging plants were also much more competitive and produced on average 23 times as many seeds per plant as spring emerging cohorts. These are very similar characteristics to black-grass.

• Delay autumn sowing to reduce Italian rye-grass infestations and ensure all plants on stubbles are destroyed pre-drilling
• Aim to achieve effective chemical control in the autumn
• Base control programmes on both pre- and post-emergence herbicides
• Herbicides such as flufenacet+pendimethalin, prosulfocarb and tri-allate are good options pre-emergence in winter cereals.
• Pinoxaden, iodosulfuron+mesosulfuron and pyroxsulam based herbicides are good post-emergence options, but vulnerable to resistance
• Apply post-emergence herbicides in autumn at the earliest opportunity according to label recommendations and soil moisture status
• Rotate herbicides over successive seasons to minimise resistance risk
• If resistance is suspected, have a seed or plant sample tested
• Hand rogue or spray off patches of rye-grass in early June to prevent seeding
• If rye-grass is sown on farms either in grass leys or as part of environmental stewardship, try to avoid it becoming a weed by preventing seed production and spread of seeds
• Consider spring cropping or fallowing to reduce rye-grass infestations, especially if resistance is confirmed

Herbicide resistance

Herbicide-resistant Italian rye-grass was first found in 1990 and now occurs on >475 farms in 34 counties of England. Compared with black-grass, there have been far fewer confirmed cases of herbicide resistance in rye-grass. ACCase (‘fop’/’dim’/’den’) and ALS (e.g. sulfonylurea) target site resistance have both been confirmed in rye-grass, but appear a lot less common than in black-grass. The main mechanism conferring resistance is enhanced metabolic non-target site resistance (NTSR) which can reduce the efficacy of most herbicides used against rye-grass.

Although resistance is currently less of an issue with rye-grass compared with black-grass, there is no room for complacency. It should be borne in mind that:

• Rye-grass species globally have shown cross-resistance to 11 different herbicide modes of action – more than for any other weed.
• The first case of a glyphosate-resistant weed in a European annual arable cropping system has recently been reported – it was rye-grass in Italy