Early indications show clear differences between winter oilseed rape varieties in their ability to tolerate verticillium wilt. Louise Impey reports

First year results from HGCA-funded trials being conducted with Farmacy on an infected site in Lincolnshire have given some useful preliminary information on variety performance in the presence of verticillium wilt.

But the work is continuing for another year, stresses Peter Gladders of ADAS, as more information is needed on the yield impact of the disease before any firm conclusions can be made about particular variety strengths and weaknesses.

“We know all winter varieties will succumb to infection,” he says. “But some will only have half the disease severity of others. That means they can finish their yield formation and come out virtually unscathed.”

In contrast, in severe infection conditions – as some growers have experienced this year – there are varieties killed by the disease, he notes. “That’s been seen at another variety demonstration site in Kent during 2010, which had 100% infection.”

Colin Button, seeds manager with Hutchinsons, confirms the Kent findings. “Some of the susceptible varieties were totally dead. There were very high levels of verticillium wilt present, so the premature ripening associated with the disease was obvious.”

At the Lincolnshire site, there was only 24% infection, he reports. That, combined with a bad hailstorm just before harvest, means the site didn’t produce any yield differences. Even so, Dr Gladders has begun to rank varieties, using a scale of 0-100.

Susceptible Castille and Kalif were used as standards in the trial. Other varieties showing a lot of disease included Es Astrid and Excalibur, although the latter still produced good field performance.

“Excalibur is interesting because it had a high disease score, but a very respectable yield. It’s a good example of why we mustn’t be too hasty with our verdict – some varieties don’t suffer as much as others.”

The early maturity of Excalibur may help, Dr Gladders suspects. “It could be that it has produced its yield by the time the disease comes in.”

One of the best performers, so far, appears to be Catana. Compass and Es Alienor have also come out well.

In the middle, with a moderate level of resistance, are a number of varieties, including DK Cabernet, Dimension, the semi-dwarf hybrids and Flash.

“Growers in England need to know what variety they should grow where verticillium wilt is present,” he points out.

“At the moment, it appears they should opt for one at the top end of the Recommended List. As yet, we haven’t tested all the varieties on the List but most of the higher yielding ones appear to be less susceptible than Castille.

“Even if verticillium causes a small yield loss, these top performers should still deliver well.”

Short rotations are believed to suit the disease, so growers should also switch to longer rotations where possible, he adds.

“If they’re reluctant to do that, then it might be worth trying Catana.”

Mr Button says there are plans to include more of the up and coming varieties in future work, so that a ranking system can be produced. Information from breeders is limited and there are no chemical control options.

“This first year has shown there are differences. With a heavy infection, all varieties succumb to the disease over time, but even where we had a moderate infection, varietal responses were recorded.”

Farm Decision

Farmacy agronomist Richard Hartley, who advises on the farm where the trial is taking place, says oilseed rape will continue to be part of the rotation, even though the disease is present.

“However, we are expanding the rotation a bit, so that rape is grown every third year instead of every other year. This will also help with weed control and the new label limitations on metazachlor use.”

He also plans to slightly delay the drilling date when temperatures have dropped a bit, in the hope that the resting spores have less time to germinate and infect the roots.

“Variety choice has been made for the coming year, but it hasn’t been based on the trials results. One year of work isn’t enough for a firm decision.”

As the main losses from the disease seem to come from late lodging, the grower has gone for semi-dwarf types, so that lodging doesn’t occur, notes Mr Hartley.

“Interestingly, they come out as having moderate resistance to Verticillium wilt in the trials,” he says. “And they’ve done very well on this farm.”