19 July 2002

Rotation major part of min-till

Getting to grips with min-till establishment, choosing wheats for wet sites and surviving without pgrs in

oats were key topics at an SAC Scottish Agronomy

open day last week. Andrew Swallow reports

GROWERS tempted to switch from traditional plough and power-harrow/drill establishment to min-till systems must rotate crops or cultivation techniques to combat the increased grassweed risk such systems will introduce.

That was one of the key messages that growers took home from the SAC Scottish Agronomys open day at Kilrie Farm, near Kirkcaldy, in Fife, last week.

"If you are going to go for min-till then the first thing to think about is what grassweeds have you got and how are you going to manage them," according to SAC weed specialist Ken Davies.

Relying on traditional in crop herbicides such as ipu, pendi-methalin and dff alone will not do.

"The problem is these herbicides will only give you 90-95% control at best and that is not good enough with grassweeds."

Trash on the surface following min-till establishment reduces efficacy, and an expensive spring follow-up treatment such as Monitor (sulfosulfuron), Cheetah (fenoxaprop-P-ethyl) or Topik (clodinafop-propargyl) is likely to be needed.

Even that should not be relied on and growers going for min-till should make use of the green bridge between crops to chit and kill grassweed seed, he says.

But the narrow window between harvest and drilling with winter crops in Scotland severely limits stale seed-bed opportunities. Hence including a spring crop in the rotation is a must, he says.

Growers should also use set-aside as a tool to clean up grassweeds and keep the plough in reserve.

"Do not throw the plough away. Keep it in the back of the barn and be prepared to bring it out perhaps one in three years."

But open day and trials host farmer John Drysdale questions that. None of his 1500ha (3700-acre) combinable cropping enterprise has been ploughed in the past three years.

"We cant afford to if we are to produce wheat that will compete with Black Sea exports."

Yields have not suffered and a flexible rotation including set-aside and spring crops has kept grassweeds in check at a reasonable cost.

"I reckon that my weed control cost averaged across all my wheat area was £15/ha this year, and that includes the Round up," says Mr Drysdale.

SAC explodes slug pressure myth

CONTRARY to popular belief min-till will not necessarily lead to more slug problems, says SAC Scottish Agronomys Eric Anderson.

"Perceived wisdom is that minimum tillage means higher slug pressure, but that is not the case in my opinion. The tillage that gives you the best seed-bed will give you the best slug control."

Indeed, there is evidence to suggest that reduced tillage allows ground beetle and carabid beetle numbers to increase. These beetles eat slug eggs, so may help reduce slug populations in the long-term, he says.

Pellets will only ever achieve a 50-60% control of slug numbers, he adds. A fine, firm, seed-bed is imperative if problems are anticipated. Growers should trap before sowing to assess risk.

"If you are catching five a trap that equates to about 10% plant damage and it is worth treating before you drill."

In wet conditions durum-based pellets are generally more durable, lasting 14-21 days, and carbamate pellets such as methiocarb or thiodicarb give a more reliable kill. "With metaldehyde the slugs can recover."

Pellets mixed in with the seed is the least effective method of baiting and an increased seed rate is cheap insurance against losses to slugs, he adds. "You have to plant enough seeds to feed the slugs." &#42

If you are going to go for min-till, you must keep a tight grip on grassweeds, says SACs Ken Davies.

Septoria surprise

Assessments of septoria in min-till and ploughed plots at Kilrie Farm has produced some surprising results, says SACs Simon Oxley. Despite trash left on the surface of the min-till plots septoria levels were lower than in wheat sown in ploughed plots. Differences in crop canopy structure could be to blame, believes Dr Oxley.

Blackgrass threat

Rough-stalked meadow grass, ryegrass, bromes and annual meadow grasses are the main threats in Scotland. But blackgrass is now encroaching south of the Forth, notes Dr Davies. "There are probably about 20 farms with blackgrass on them north of Morpeth now. If that weed is around, then min-till will encourage it," he warns.

&#8226 Beware grassweed build up.

&#8226 Rotate winter & spring crops.

&#8226 Glyphosate green bridge.

&#8226 Do not dump the plough.

Claire and Deben (left) survived waterlogging, where most varieties perished, points out SACs Eric Anderson.

Growing oats without straw stiffeners is a substantial risk – premiums need to reflect that, says SAC Scottish Agronomys Huw Phillips.

Wheat beats wet feet

SOME varieties of wheat will cope with wet feet in winter better than others it seems.

In SAC trials, prolonged water-logging wiped out most plants in many varieties, but Claire and Deben survived to produce a normal stand. They stand out as being totally different," says SACs Eric Anderson. "We believe it is something to do with the root structure."

The probable explanation is that the varieties have more aeroenchyma tissue in the roots than others, he says.

This special tissue, found in large volumes in the roots of rice, transports oxygen allowing roots to survive when underwater.

Wheat is known to have more aeroenchyma tissue than barley, hence wheats greater tolerance to water-logging. The findings at Kilrie Farm suggest there are notable differences between varieties of the same crop, too, he concludes.

Straw issue in pgr-free oats

DANISH demand for oats grown without straw stiffening products is posing some tricky agronomy questions for growers in Scotland, says SAC Scottish Agronomys Huw Philips.

Contract premiums fail to recognise the risk growers are taking by cutting out chlormequat and Moddus (trinexapac-ethyl), he believes.

"They are paying £8-10/t premium at present. That may be enough once we get to grips with the agronomy, but it is not enough now. £2.50/ha is the only saving for a lot of risk."

Trials are in progress to draw up a reliable crop protocol, but in the meantime the advice to spring oat growers going for the pgr-free market was to cut seed from 400 to 300 seeds/sq m and apply split dose Landmark (kresoxim-methyl + epoxiconazole).

"Landmark has given some standing power differences in previous trials."

Scope to reduce nitrogen below 100kg/ha (80 units/acre) is limited for fear of raised screenings and reduced specific weight, he adds.