9 January 1998

Ns wasted on stressed rape

ROUGH looking rape crops may need a fungicide soon. But dont be tempted to pep them up with a dose of nitrogen – any fertiliser applied now will be money down the drain.

That is the advice from ADAS consultants as the winters wet weather takes its toll on the crop.

"There are always some odd looking crops about at this time of year as stress sets in," says Cambs-based John Garstang. Viruses and sulphur deficiency as well as the more normal fungal problems of phoma and light leaf spot can all be to blame.

"But a lot of poor crops are probably suffering more from wet feet." The give away is the red and purple tissue, especially of the more susceptible younger plants.

Disease control may be required soon, especially if no autumn applications were made, advises Mr Garstang. "But growers certainly should not be applying nitrogen yet. Even for the most forward crops February should be the earliest timing." Dressings now would be mostly washed out and wasted, he explains.

Phoma is developing quite rapidly even in some fields treated in October, notes colleague Peter Gladders. "Ideally wed like to see them treated in January to stop the disease getting to the stems." Stands with smaller plants should take priority, he advises, since the fungus has less far to spread from the leaves and cause canker.

The big increase in autumn treatments should be holding light leaf spot in check, notes Dr Gladders. Growers should concentrate inspections on the more susceptible varieties like Apex.

If the weather is wet and windy it is easier to spot the tell-tale white spores of the disease if samples are put into polythene bags for a couple of days, he adds.n


&#8226 Stressed crops.

&#8226 Range of causes.

&#8226 No nitrogen needed yet.

&#8226 Phoma control main priority.