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Stopping the spread of clubroot

Whether you’re trying to keep clubroot from infecting your soil in the first place, or stop it from moving from field to field, there are strategies to use

By the time you find a patch in your field that’s infected with clubroot, Clint Jurke, agronomy specialist with the Canola Council of Canada told delegates at the International Clubroot Workshop in Edmonton in June, “that disease has probably already been in the field for years.”

In fact, it’s likely already spread to the rest of your farming operation. At this point, Jurke said, “the cat’s already out of the bag.”

Jurke presented eight things that won’t stop the spread of clubroot.

Eight things that won’t stop the spread

1. Fungicides Fungicides will reduce yield damage in infected plants, but won’t fix the root cause. However, “they stop infection. They’re not eradicating the clubroot from the soil.”

2. Seed treatments Clubroot spores can spread in dirt that comes attached to seed that’s imported from an infected area. Seed treatments will keep this from happening.

However, if you already have clubroot spores in your field, seed treatments won’t kill them. Jurke said, “Seed treatments will kill that pathogen that’s on the seed, but not the pathogen in the ground.”

3. Boron Researchers have been studying the effect of boron on clubroot. “Boron will reduce clubroot infestation,” Jurke said. Unfortunately, “the concentration of boron that’s required is phytotoxic to the canola plants.” In this case, the prevention is worse than the cure.

4. Liming High pH soils have been shows to be associated with lower incidence of clubroot infection. However, Jurke said, “having high pH soils will not stop clubroot from arriving on your farm.”

Jurke says, “This might be a tool that we can use to kind of slow it down, but it’s not going to be the most cost effective.”

5. Other soil amendments Researchers are examining other soil amendments, such as calcium carbonate. So far, nothing has been found that isn’t cost prohibitive.

Jurke says, “In a cost-benefit analysis, these do not work.”

6. Bait crops Researchers have been testing the possibilities of using bait crops to convince the crops to germinate, then destroying the spores. So far, Jurke said, “It hasn’t panned out.”

7. Tillage Not only will tillage not kill clubroot spores in your soil, adding more operations and traffic to your field could actually help the spread of the disease. Additional tillage can also lead to soil erosion, which can help spread clubroot spores.

8. Crop rotation Crop rotation can slow the increase of clubroot spores in the soil, but it will not eliminate the spores or stop clubroot from arriving in your field.

So what can you do?

Slowing the spread of clubroot

1. Crop rotation While good crop rotations won’t stop the spread of clubroot, growing canola on canola stubble will increase the amount of inoculum in your soil.

“Where a longer crop rotation actually works is in conjunction with resistant varieties,” Jurke says. “A long rotation is not enough if you’re using susceptible or moderately susceptible varieties.”

2. Clubroot resistant varieties Resistant varieties can help farmers with infected soil continue to grow canola. “Resistance is our saving grace,” Jurke said. However, he added, “It’s not bulletproof.”

If farmers put too much pressure on resistant genes, Jurke said, “you will eventually start selecting for the clubroot to overcome resistance.

“We do have two sources of resistance,” Jurke said — one developed by Pioneer Hi-Bred and another developed by Monsanto. Jurke suggests farmers maintain recommended crop rotations, and also rotate clubroot resistant seed between the two types.

3. Seeding date “The earlier you plant your canola,” Jurke said, “the better your chances.” As soil temperature increase, clubroot can spread faster.

4. Sanitation “Sanitation is our best weapon to really help control the spread of disease,” Jurke said. “But it is a big cost.” Effectively cleaning and disinfecting farm machinery to the point where not a single clubroot spore could survive is time consuming. “Sanitation has to be used in a strategic fashion,” Jurke said.

5. Early identification “if you can find clubroot when it first arrives in your field,” Jurke said, you may be able to quarantine it in a small area.

6. Reduced tillage Reducing tillage “will reduce the amount of wind and water erosion,” Jurke said. Also, travelling over the field less will give spores fewer opportunities to move around the field.

7. Quarantine/isolation Clubroot spores are more likely to be near the field entry point. “Ninety per cent of the time that is were you’ll find the pathogen first,” Jurke said.

If you find clubroot at the field entry point, you might consider grassing in that area, or moving the approach to the field to a new location. If you isolate that area, Jurke said, “you don’t have to treat the whole farm as being infested.”

8. Eradication Researchers are looking at fumigants as an option to totally eradicate clubroot spores from the soil. So far, Vapam is showing some good results.

However, while Vapam is effective in greenhouse studies and plot-sized areas, it is not yet cost-effective on a field scale. “That is an option that we do need to explore a whole lot more,” Jurke said.

9. Brassica weed control Canola is not the only plant that clubroot will attack. The spores will also attack weeds in the Brassica family. These include wild mustard, stinkweed and shepard’s purse. A large population of Brassica weeds in your field, Jurke said, “could be propagating that disease.”

10. Planning In developing a clubroot strategy, remember that if you’re growing wheat in your field, the clubroot spores are still there. For example, if you’re moving harvest equipment from an infected field to a clean field, you should sanitize your equipment, Jurke said, “even when it’s not a canola year.”

11. Inputs Seed imported from an area infected with clubroot can bring the pathogen with it. Cleaned, treated seed, Jurke said, “can reduce the pathogen to almost zero.”

This doesn’t just apply to canola. Spores can also travel with bin run barley seed imported from an area infected with clubroot.

12. Management plan Coming up with a plan to prevent clubroot and identifying it early if it does reach your field can help prevent the spread of clubroot. †

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