Cabbage stem flea beetle (CSFB) is moving into areas where it has rarely been seen or only seen at low levels before with devastating consequences for some oilseed rape crops under attack from larvae in the stem or leaf petioles.
Martin Smart, who farms in Wiltshire and has hosted many oilseed rape trials over the years says he has lost 70-80ha of a total of 350ha of oilseed rape to CSFB. “We are really badly affected - I had hardly experienced flea beetle damage before – nothing like this. A lot of crops in the area have been ripped up in the last 10 days.
“It is heart breaking and soul destroying. Field walking here has never felt like this. I have never experienced crop failure like this.”
Mr Smart says in one local crop he found 4-5 larvae with some affecting the stem and some, side branches. “Where it is bad they are taking the main stem and plants are disappearing. When you walk it, tell-tale signs are any stem that looks like an over-ripe banana and is a mustard colour. It takes the vigour out of it and it cannot get away.”
Looking back to autumn, Mr Smart says spraying CSFB with pyrethroids and Biscaya (thiacloprid) seemed to have no effect. “We sprayed at cotyledon stage and it was a losing battle. You felt as though you were doing something to spray but you would have been better staying at home.”
He says that OSR planted near forage maize or woodland, which harbour CSFB, has fared worst. “You plant rape then the forage harvesters go into maize. The beetles come out of maize on an air stream and land in crops of freshly emerging rape and off they go.”
In terms of husbandry practices to reduce beetle attack, Mr Smart says precision drilling helps. “Where it is precision drilled, all plants emerge together and there are too many for the flea beetle to take out.”
There are also varietal differences, he says. “Even some of the leading varieties were wiped out. SY Harnas was fine. Alizze on heavier land seems to be the most forward crop.”
He is disappointed that a variety in a trial on his farm which was hardly affected by CSFB and had high vigour was discounted by the company trialling it because its disease resistance scores were deemed to be too low. “You can manage a low disease rating but you cannot manage with no crop,” says Mr Smart.
Independent agronomist Ben Boothman of B M Boothman Agronomy covers North Yorkshire and says it has not been uncommon to find more than 30 CSFB larvae in an OSR plant. “Now rape is really starting to move we are noticing differences – healthy plants are jumping away but those destroyed by larvae are not growing at all.”
While it is difficult to put a figure on crop lost to CSFB, Mr Boothman says in affected areas such as the Vale of York, 50-80 per cent of crop can be lost in a field. “It is so varied – around Ossett there is little damage and Scotch Corner, very little.”
He believes the fact more OSR is grown in the Vale of York and that warmer temperatures for longer in autumn meant CSFB stayed active for longer may account for why this area was worse affected than other parts of his territory.
However, even where 50 per cent of the crop has been lost, there is still chance of a reasonable yield, says Mr Boothman. “Plants can compensate. All rape should have had half of its fertiliser dose and make sure all fertiliser is on by the end of this month,” he advises.
During the recent spell of warm weather ADAS set yellow water traps in some plots of oilseed rape. The traps caught a number of pollen beetles. This is one of the earliest records it has of pollen beetles in crops and the early migration of these pests was confirmed by their presence in Rothamsted suction traps across the country, according to senior ADAS research scientist Steve Ellis.