The survival of many oilseed rape crops hangs in the balance as slow growth and high slug pressure take their toll.

Up to 50% of fields nationally are at medium to high risk of failing to make it through the winter, according to Agrii business development manager David Neale.

“Crops are under incredible pressure. Some will pull through, but we are potentially looking at a 20% reduction overall in the winter crop area, and that could be optimistic.”

Low temperatures and wet soils meant many crops have hardly moved in the past few weeks, Mr Neale says. Slugs are ravaging plants, especially on fields that were mauled in late.

Some fields have already been sprayed off. But most are too wet to do anything with and are likely to remain that way for weeks or months, he adds.

Weather, pests and disease over the autumn and winter would be a key factor governing crop development and survival, says United Oilseeds technical manager Richard Elsdon.

Areas worst affected include those north and west of a line from Bristol to the Humber, and in the far South East where seed had lain in dry soil for weeks before the weather broke.

“Slugs are rampant in many crops and pigeons are queuing up. Some growers have put bangers out already.”

Phoma was a real threat to small, backward crops, he adds. “How quickly farmers respond will be critical.” A fungicide should be applied once 10% of plants were infected, he says.

Although East Anglia had fared best, it had its share of problem crops, says Frontier Agriculture’s technical manager Bob Mills. Sub-cast fields were hard hit, with difficult-to-close slots creating a “motorway feeding station” for slugs.

Some growers have reached the 210g ai/ha advisory limit for metaldehyde. Methiocarb is difficult to find, and although ferric phosphate is more available, there were on-farm concerns over cost and efficacy, Mr Mills notes.

Growers must give crops every opportunity to do well. “Unless you have decided they won’t survive, take cereal volunteers out. For crops yet to receive it, metazachlor can go on at the same time.”

Propyzamide/carbetamide programmes should also be followed up where possible. “Provided you have 25-30 plants/sq m fairly evenly spaced, I would go.” However, in the event of crop failure, a plough will be needed before spring planting, he adds.

Herefordshire-based AICC agronomist Antony Wade says many growers have applied their two half rates of metaldehyde and are now applying ferric sulphate.

About 20% of his area is looking poor, and spraying decisions are proving difficult. “I have just come off one farm where the farmer has decided not to risk the expense. Slugs are everywhere, and seem to be worse where seed-beds have come down well.”

• Slugs, cold weather and wet soils taking toll
• 20% reduction in winter crop area likely
• Difficult management decisions
• Give all but worst crops a chance to perform
• Wait until spring to assess poor crops’ chances