Ryegrass trouble on the increase
Ryegrass trouble on the increase
By Andrew Blake
AVOID sowing ryegrass, especially Italian ryegrass, on set-aside, warns Oxon-based AICC member Laurence Sim.
Only a limited range of herbicides controls the grasses in following arable crops and resistance in Italian ryegrass restricts the choice still further, he explains.
Ryegrass damages output. Just five plants/sq m in a typical winter wheat crop will cut yield by 8.5%, US work suggests.
"It is very competitive in early spring and responds well to nitrogen, fungicides and growth regulators," says Mr Sim. "It germinates from the autumn right through to May and produces lots of seed which sheds before harvest. And although perennial ryegrass seed persists for only 3-4 years in the soil, Italian may still be present after seven years."
His recent survey of AICC members drew 67 reports, with only 12% – mainly in East Anglia, the north and Scotland – not considering ryegrass to be a problem. "Overall about 9% of all arable fields contained ryegrass. 4% had Italian ryegrass alone, 3% perennial only, and about 2% mixed populations."
The figures are similar to findings in 1981 and 1993, he says. "The problem is that none of the selective products currently available gives consistently high levels of control. There are also now over 30 confirmed cases of herbicide resistance in Italian ryegrass in 12 counties, though thankfully none so far in perennial ryegrass."
Miss one seasons control and a slight infestation will soon become troublesome, he warns.
AICC feedback suggests more than one treatment per crop may be needed, especially where emergence is protracted. Comments on control from active ingredients in wheat include:
lTri-allate – Good effect as part of a programme.
lTralkoxydim – Can give very good results, but many also poor.
lIsoproturon – Poor to moderate.
lChlortoluron – Better than IPU but over-spraying often needed.
lPendimethalin – Variable.
lFlupyrsulfuron-methyl – Poor to acceptable.
lDiclofop-methyl (no longer available as straight) – Good on small plants.
lClodinafop-propargyl/trifluralin – Can be good on small plants.
A few of the poor results after tralkoxydim (as in Grasp) could be attributed to resistance, Mr Sim believes. Six per cent of survey respondents had at least one confirmed case of resistance, and 22% suspected resistance but had no supporting evidence.
The choice of ryegrass graminicides for breaks is more restricted still, making cultural control even more important. "Its also worrying from an anti-resistance point of view that five of the seven products for use on oilseed rape are fops or dims." Results from the other two, carbetamex and propyzamide, can be quite variable, he says.
"Clearly its inadvisable to base set-aside green cover on Italian ryegrass. But growers need to think about every means of preventing ryegrass taking hold in the first place." These include careful grazing and cutting of grass breaks to avoid seeding, spraying off with glyphosate before ploughing and employing stale seed-beds.
"It is worth remembering that ryegrass seed can be carried between farms in seed, straw and combines. One AICC respondent thinks Italian ryegrass got on to one farm in straw used to cover carrots." *
Ryegrass problems are increasing, warns AICCmember Laurence Sim.
RYEGRASSTHREAT
• Nearly 10% of arable fields infested.
• Highly competitive and persistent.
• Limited range of useful herbicides.
• Avoid introducing through set-aside.