Spray for sclerotinia or give it a pass? That’s no simple black or white question, but one thing is certain — by the time you can see it, it’s too late.
Anastasia Kubinec, Manitoba Agriculture, Food and Rural Development oilseed specialist, said that doesn’t mean you shouldn’t scout though. If anything it means it’s more important than ever to manage a disease that relies on specific environmental conditions to flourish, including dense stands and elevated moisture levels in the crop’s canopy.
“And you can’t tell that when you are driving by — you really do need to walk through it,” Kubinec said. “I think for assessing for sclerotinia application, scouting is very important because you do need that humidity and moisture in the canopy to have the infection take hold in the plant… if it is really dry, even if there is some infection the actual sclerotinia infection can dry up and then you don’t get the yield loss.”
The spraying window usually falls when the plants are between 20 and 50 per cent in bloom.
“You’ve got to go in and spray before you see symptoms in the field, that is why you have to go through that checklist of environmental factors and your practices to see if spraying is warranted or not,” said Justine Cornelsen, an agronomy specialist with the Canola Council of Canada.
Both the province and the canola council offer online calculators to help producers make the decision whether or not to spray.
However, Tim Gardner, a senior market development specialist at Bayer adds that the fight against sclerotinia should begin before seeds are even in the ground, when producers are still planning out their crop rotations.
Having gathered questions about the fungus from farmers across the Prairies, Gardner said there are still myths out there about which crops can host the disease and which cannot.
“Rotations are definitely another important consideration,” he said. “We are running crop rotations pretty tight on the whole… and the thing is that sclerotinia is not just specific to canola, there are a lot of bridge rotation crops, it could be sunflowers, it could be peas, lentils, dry beans, all of the above.”
The sclerotia bodies that cause the disease can also live in soil for as long as 10 years, said Cornelsen.
“That’s why the recommended rotation if it is canola is at least four years before having it in field again,” she said. “Although that can be hard to justify because you are going to have spores blowing in from the surrounding fields and you can’t control what your neighbours are doing, so the chances of infection are probable.”
Some weeds are also hosts for the fungus, meaning even empty fields or ditches can hasten the spread of spores.
As much as evaluating environmental factors is key in predicting and preventing sclerotinia losses, so too is the evaluation of economic factors.
“It usually ends up boiling down to return on investment,” said Gardner. “Factor the cost of application — and obviously the product — then going out and leaving wheel tracks in the field.
“I fully admit that there are years where I have seen just break-even numbers on it as well, and then the hard part about it is that I’ve also seen the hard years where people are losing up to 15 bushels per day per acre,” he said.
Cornelsen offers a rough guide for the economics of spraying.
“If you figure yield potential is over 30 bushels an acre it is just a safe insurance to spray,” she said, provided you have a high number of risk factors.
Kubinec adds producers also need to calculate their margins carefully, looking at market conditions as well.
“With 30 bushels per acre you have to know how much you are making per bushel too, if you’re only making $6 a bushel on canola — and I hope we never get there again — 30 bushels isn’t going to pay for it. Not with your application costs, whether they are going to have to get someone to custom do it, if they have their own equipment to run, as well as the product,” she said.
And while the 2016 planting season is just getting underway in Manitoba, it’s not too early to start thinking about sclerotinia, even if it’s too early to predict what disease incidents will emerge. Last year’s canola disease survey found sclerotinia was present in about 70 per cent of Manitoba fields.
“It had an incident rate of probably around 15 per cent, but it is still present,” said Cornelsen. “And if we give it the perfect conditions it will take off.”
That said, producers do have excellent tools available to them, Kubinec added.
“With canola the products that they have and timing they have figured out, if guys can assess their risk and they are going to use the products, they do work very well when applied at the right time,” she said. “I mean you may still have a little bit of sclerotinia in the crops, but it’s not the 50 per cent or the 80 per cent yield lost that guys were getting in the early ’80s when there were no products to use on canola.”