Date: 07/2021

The tighter arable rotations used by growers in recent years, an increasing number of large mixed farming operations and greater use of brassica elements in cover crops is making Clubroot a growing threat to oilseed rape growers.

With spores that can last in the soil for up to 20 years many crop producers could be vulnerable to flare-ups resulting from farm practices carried out as far back as the 90’s, says Frontier regional seeds manager David Waite.

“Clubroot can easily take out 50% of your yield so it’s something you need to take seriously. Furthermore, it’s spread pretty widely across the UK now so few areas are completely safe.

“Spores from previous Brassica crops, including cruciferous weeds, kale, turnips, swedes and mustard frequently used as cover crops, can survive in the soil for many years before spouralating when a suitable host crop emerges.”

“If this is oilseed rape, large root galls form on the taproot which ultimately decay and break open releasing more of the Clubroot pathogen back into the soil and also allowing secondary rots to enter the root which severely affect their function, reducing water and nutrient uptake.”

As the season progresses plants wilt, become very stunted and are eventually lost completely, he explains.

“Wet conditions allow spores to disperse and infect roots with flooding accelerating spread of the condition but it can also be caused by soil transfer from machinery, the storing infected vegetables, such as Swedes, on land or the dumping of vegetable waste.

Scottish problem

Clubroot can even be spread from the manure of animals fed on infected produce, David Waite adds.

“That’s probably why the North of Scotland suffers so much as such a large proportion of farms are mixed with a significant area of swedes and turnips grown to feed stock.

“Over the years, I would say 75% of all oilseed rape sold in the North of Scotland is Clubroot resistant which falls to 50% in Central areas and then 25% in the South.”

“If you have Clubroot on your farm it’s black and white really. Don’t grow oilseed rape or at least choose a resistant variety.”

Crocodile CR is the highest yielding clubroot resistant oilseed rape to join the 2020/21 AHDB Recommended List by a significant margin, says DSV’s Mike Farr.

“With a seed yield of 104% of control in the 2020/21 RL Crocodile is right up there with the very best mainstream hybrid oilseed rapes in terms of outright performance.

“It 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.”

“2019 saw a 20% increase in plantings of clubroot resistant varieties over 2018 and this rate of increase is likely to continue over the next few years.”

Growers choosing clubroot resistant varieties have traditionally had to pay a yield penalty Crocodile CR changes all that, he adds.

“Crocodile CR hasn’t just closed the yield gap, it’s reversed it with many of the highest performing varieties on the current Recommended List struggling to keep up with it.

“When the variety joined the candidate list November 2019, it was the first ever Clubroot resistant variety to get there on its own merit without special dispensation.

“As well as strong development in the autumn, the variety is also quick to get going in the spring, rapidly developing lower buds.

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, Mike Farr emphasises.

A real lifeline

“It’s not infallible and, like other resistant varieties, may be infected by some strains and infections that have been reported in some fields so it is important that growers protect its genetics by only planting the variety where Clubroot is known to be an issue.”

Frontier’s David Waite agrees saying whilst many of the features of Crocodile CR would make it a good choice for growers without Clubroot problems, this is not advisable.

“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.

“Acidic soils and warm, wet weather can increase incidence of the disease with more variable growing conditions and increased numbers of flooding events adding to the problem.

“Longer term, lengthening rotations is the most sustainable long-term strategy for managing Clubroot, but a strong variety like Crocodile CR can do much to deliver consistent yields and performance where a problem is already actively affecting growth.”