Clubroot resistant oilseed rape varieties have a valuable role to play in controlling the rise in clubroot across the UK, but their use should not be an excuse for replacing good cultural control, says DSV UK technical manager Andrew Hartley.
Clubroot is a problem in oilseed rape brought about mainly by close rotations and acidic soils but the way we have changed our drilling pattern in oilseed rape to offset flea beetle pressure is also making it more of a concern.
Able to survive in the soil for 15-20 years in the form of resilient resting bodies and able to survive on cruciferous weeds like Shepherds purse and Charlock, it’s a big problem to some growers and maybe becoming a bigger threat to growers not used to the problem.
The move to the earlier drilling of oilseed rape when soils are warm and the wetter milder autumns have increased the risk, flooding and residues from livestock on different feed types could also play a part. The increased use of cover crops could also be a contributing factor.
Symptoms appear as patches wilting in the field, stunted growth, swollen misshapen roots which rot and in the process re infect the soil. Severe infections can lead to 50% yield loss.
Of course we know acid soil is a big contributor to the problem so addressing that is a key step forward. Rotation of oilseed rape shouldn’t be more than 1 in 5, preferably wider, and we have seen other benefits to adopting this approach.
Improving drainage and restricting soil movement from infected areas is also vital to avoid spreading infection.
Resistant varieties key
Resistant varieties are also highly important and effective but should not be relied upon by themselves if you are growing the crop in a shorter rotation.
Growing such varieties without appropriate cultural controls will quickly breakdown the genetics providing the resistance.
Without doubt the most successful clubroot resistant variety currently available in the UK is DSV Crocodile CR.
First listed on the 2020/21 AHDB Recommended List, Crocodile CR was the highest yielding clubroot resistant oilseed rape to join the RL by a significant margin.
With a seed yield of 106% of control, the variety was right up there with the very best mainstream hybrid oilseed rapes in terms of outright performance.
Today Crocodile CR still convincingly outyields the other recommended clubroot resistant varieties, making it the perfect choice for growers in regions where the condition is becoming an increasing problem.
Significant yield advantage
As well as providing strong protection against the condition, Crocodile CR means growers don’t have to suffer the traditional yield penalties that come with choosing a clubroot resistant variety.
As well as its yield advantage, it’s got the same 45 day rapid establishment period of many DSV top performers and is also quick to get going in the spring, rapidly developing lower buds.
features a really strong agronomic package with an 8 for resistance to lodging, a 7 for stem stiffness and the all important 6 for light leaf spot on the 2022/23 RL
But whilst Crocodile CR’s performance is impressive, it’s important to remember the variety is recommended for growing only on land infected with common strains of clubroot.
It’s not infallible and, like other resistant varieties, may be infected by some strains and infections, so it is important that growers protect its genetics by only planting the variety where clubroot is known to be an issue.
Longer term, lengthening rotations is the most sustainable long-term strategy for managing clubroot, but Crocodile CR can do much to deliver consistent yields and performance where a problem is already actively affecting growth.
Crocodile CR offers a real lifeline for oilseed rape growers with serious clubroot problems but if you feel you are at risk, it’s a good idea to carry out a soil test.
It’s always worth monitoring the situation on mixed farms and if you’ve historically used tight rotations.