Clubroot is becoming a bigger issue in UK oilseed rape crops, with resistant varieties and rotation issues playing a key role.
Traditionally regarded as something of a niche problem when compared to light leaf spot and phoma, clubroot is typically confined to northern England and Scotland.
But incidence appears to be increasing elsewhere, with the potential to cause significant yield losses of up to 50 per cent in the worst cases.
Hutchinsons technical support manager Duncan Connabeer says: "Clubroot is becoming more of a problem for some growers, although there is no clear regional link.
"The West Midlands has been a problem area for the disease, but it is occurring elsewhere, with reports of crop loss in some situations. Incidence tends to be patchy and not normally over large areas but, even so, there are cases of patches covering one or two acres, which is an appreciable size."
The clubroot pathogen, Plasmodiophora brassicae, favours higher temperatures - development stops below 15degC, plus moist and acidic - pH 6.5 and below - soil conditions so the increasing frequency of warm, wet weather in autumn through to spring could be a factor, he suggests.
"In general, conditions that favour take-all in cereals also favour clubroot."
Cropping and rotation are also big risk factors, Hutchinsons technical development director Dr David Ellerton adds: "Clubroot tends to be more of an issue in vegetable growing areas where there are, or have been brassicas in the rotation.”
Close rotations of any susceptible crops, such as oilseed rape, turnips and swedes, or dumping infected vegetables on land both increase the risk, he says.
Indeed, northern technical manager Cam Murray cites the example of one farm in southern Scotland where patches of clubroot have been linked to past dumping of turnips on those parts of the field years ago.
He too believes disease incidence is increasing, particularly in areas where brassicas have been grown for vegetable production or livestock feed.
"Clubroot can survive in the soil for 15 years so, once it is there, it will be around a long time.
"You have got to keep the rotation 'clean' which, for most growers with other brassicas in the rotation, means not growing oilseed rape on that land."
Mr Connabeer adds Brassicas that have been grown for game cover or cover crops could also potentially increase clubroot risk.
TACKLING INFECTED AREAS
Sowing a resistant varietv Is often the main option for many growers, but Hutchinsons northern technical manager Cam Murray says this must be integrated with other cultural measures to prevent the pathogen overcoming genetic resistance.
In his home country of New Zealand, where clubroot is the main focus for breeders of new turnip and swede varieties, genetic resistance has broken down in as little as two years, he says.
"We have not seen anything as dramatic in the UK, but It demonstrates the pathogen's capability to evolve, so we have to manage it carefully."
Mr Murray says DK Platinum is the main resistant variety grown in his region this year. "It has got good scores for phoma and light leaf spot, establishes well and looks good so far."
Clubroot control tips
- Avoid short oilseed rape rotations -ideally no closer than one year in 7 or 8
- Apply soil amendments (for example lime) before drilling to raise the calcium content and soil pH to 7 or above
- Rectify any drainage issues
- Control cruciferous weeds that may carry over disease (for example shepherd's purse, charlock)
- Grow resistant varieties, but avoid over-reliance on short rotations (no more than one year in 4 or 5)
- Avoid transferring disease to clean land by dumping infected vegetable waste or spreading manures from animals fed on infected produce
- Clean infected soil from cultivation equipment before moving fields
- Avoid growing oilseed rape on severely infected sites
- Soil test land destined for oilseed rape to assess risk before drilling especially if its previous cropping history is unknown