8 October 1999

Better grassweed control can minimise ergot risks

By Andrew Swallow

AGRONOMISTS and research-ers urgently need to find an answer for ergot, says Paul Warburton of North Farm, Shillingford, Oxon.

"The losses can be nearly £50/acre, and when you ask the experts how to control it, they just go quiet. Nobody seems to know anything about the disease," he says.

ADAS Boxworth cereal specialist Bill Clark admits there is an element of truth in that. But there are things growers can do to minimise the risk based on current knowledge.

"Mostly its about grassweed control and, Im afraid, it comes down to variety. If youve had problems with ergot, you have got to pick your varieties better," he says.

Ploughing can help too, as resting bodies are destroyed when buried for a year. "If growers have had a field infected with bad ergot this year ploughing would be well worthwhile. That will have a dramatic eff-ect on inoculum next season."

But Mr Warburton ploughs the whole farm as a matter of routine, taking care to bury all trash. "Its an expensive and slow job, so one might as well do it properly," he says.

Grassweed control is also comprehensive, with little blackgrass and only a few patches of couch on the farm. In fields hit by ergot this harvest either a full-rate tank-mix of Lexus 50DF (flupyrsulfuron-methyl) with 1.5 litres/ha Stomp (pendimethalin), or a mix of ipu/dff/pendimethalin was used last autumn. "The crops were pretty clean," he says.

But spores are airborne and will travel tens of metres, says Mr Clark. That means even weed-free crops can be infected from hedgerow grasses. Mr Warburton accepts this is the likely source of infection at North Farm.

"We have a lot of hedges with wide grass margins, and its a windy, exposed farm," he says. But removing the margins or hedges is ruled out, despite the ergot issue.

"We should be doing these things in all other respects. They keep weeds like brome out of the crop."

Topping margins might be an option, de-laying spore release by delaying grasses flowering until after wheat has flowered. But that would eliminate wild flowers from the margins and add costs.

Switching variety is an option growers of ergot-infected Rialto should consider, says Mr Clark.

But Mr Warburton had no Rialto. "Reaper was dropped because it had bad ergot last year. This year its in all the Consort and Soissons – its the Soissons that really narks me – yet Savannah has had no problem."

The only known ergot fungicide is carbendazim applied to coincide with flowering, but control is far from complete, warns Mr Clark. &#42

TACKLING ERGOT

&#8226 Plough after infected crops.

&#8226 Avoid susceptible varieties eg Rialto.

&#8226 Control grassweeds.

&#8226 Mbc at flowering some effect.

Grass field margins are suspected of harbouring the inoculum which has infected wheats on Paul Warburtons farm for two years.

Ergot explained

Infection of cereal crops is either direct from spores released from resting bodies germinating on the ground, or from ergot-infected grasses. Spores are airborne and can carry from one field to the next, or from a hedgerow into the middle of the field. However, there is a strong correlation between ergot incidence in wheat and the level of blackgrass in crops, says Mr Clark. Other species host the fungus too, including ryegrasses, timothy, and annual meadow grass, and there are numerous strains of ergot itself. "Its not clear which cross-infect to wheat," he says. Rialtos susceptibility is due to the open flowering habit of the variety. "The glumes gape wide open at flowering. The wider they open, the more chance of spores infecting wheat ovaries," he says. Cool, moist conditions at flowering favour infection.