Knowledge Hub Article

Italian Rye-grass - Weed Management

Italian Rye-grass is an annual grass-weed propagated solely by seeds and, if uncontrolled, weed populations can increase rapidly.  

For successful long-term control, seed return must be minimised. Italian Rye-grass has a very similar biology to black-grass in terms of emergence patters, 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 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.

Herbicide resistance

First found in the UK in 1990, over 475 herbicide-resistant populations have now been identified in 33 counties of England.  Populations show variable degrees of resistance to a wide range of different modes of action.  ACCase and ALS target site resistance (TSR) occur much less commonly than in black-grass, although this type of resistance is likely to increase.  Non-target site resistance (NTSR), especially enhanced metabolism, is the most widespread type of resistance – as it is in black-grass.

 

Type of resistance

Mechanism

Non-target site – principally enhanced metabolism

Results in herbicide detoxification and is the commonest resistance mechanism in rye-grass It affects most herbicides to varying degrees, but only in severe cases results in complete loss of control.  Tends to increase slowly.

ACCase target site

Blocks the site of activity specific to ‘fop’, ‘dim’ and ‘den’ herbicides.  It only affects these groups of herbicides, but often results in very poor control and can increase rapidly.  Detected much less frequently than in black-grass but likely to be increasing rapidly.

ALS target site

Blocks the site of activity of sulfonylurea and related herbicides.  It only affects these groups of herbicides, but often results in poor control and can increase rapidly.  Found for the first time in 2012 in UK populations of rye-grass - much more recently than in black-grass.  Appears to be much less common than in black-grass but likely to be increasing rapidly.

 

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
Control – herbicides

Pre-sowing – destroying all emerged rye-grass plants before sowing a crop is essential, especially if they are well established.  Use of glyphosate can ensure a better degree of kill than cultivations alone.

Pre-emergence herbicides – flufenacet + pendimethalin, prosulfocarb and tri-allate are good options pre-emergence for control in winter cereals and efficacy is usually only partially reduced by resistance.

Post-emergence herbicides, such a pinoxaden, iodosulfuron + mesosulfuron and pyroxsulam based herbicides are good post-emergence options in cereals, but vulnerable to resistance. Propaquizafop, cycloxydim, clethodim and carbetamide can give good control of susceptible rye-grass in a range of crops, but resistance to most of these herbicides is likely to increase.

  • 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

Pre-harvest – established perennial and Italian ryegrass can be controlled effectively using glyphosate applied pre-harvest in a range of cereal, pulse and oilseed crops.

Non-chemical control

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

  • Delay autumn sowing to reduce Italian rye-grass infestations and ensure all plants on stubbles are destroyed pre-drilling
  • Spring cropping can reduce rye-grass infestations although may need to be repeated for two or three years to achieve adequate reductions in severe infestations
  • Fallowing or growing grass leys for 3 years or more can be effective at reducing weed seed populations in the soil but only if seed return is prevented
  • Competitive crops, such as spring barley, sown at relatively high seed rates will help suppress rye-grass
  • 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
  • Ploughing can be effective at burying freshly shed seeds to a depth (>10 cm) from where plant emergence is unlikely, but good inversion is essential
Future issues
  • Resistance to pre-emergence herbicides – how quickly will it increase?
  • Will there be any new herbicides?
  • Availability of herbicides – how many will we lose through EU and individual country’s regulatory decisions?
  • Will resistance to glyphosate develop widely?
  • Cost of non-chemical control measures – can farmers afford these?