Growers who run short rotations and over use fungicides risk losing their magic bullet in the war on plant disease.
Lentil breeder Bert Vandenberg has a name for market chasing producers who put pulse crops on short rotations and routinely spray fungicides on everything – fungus breeders.
Their practices can cause disease mutations that overcome the resistance that has been bred into current varieties. When that happens, fungicides, a grower’s last line of defence, can also become useless.
“We all know we shouldn’t push our rotations, but there are people who do it anyway,” says Vandenberg, a plant researcher at the Crop Development Centre at the University of Saskatchewan in Saskatoon.
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“Short rotations automatically give a biological advantage to the fungus. It helps them mutate and adapt.”
He says growers make the problem worse when they try to compensate for short rotations by spraying fungicides. Applying fungicides routinely to a whole field gives the disease more chance to develop tolerance to the chemical.
Short rotations and routine fungicide use have also become more common in cereals, oilseeds and other pulse crops. As well, a similar scenario of increasing pesticide tolerance is playing out with weeds and insects.
Vikram Bisht, a plant pathologist with Manitoba Agriculture, says mutant fungi use two different schemes to escape human efforts to control them.
He said the pathogen is continually mutating to overcome resistance bred into the plant and is also mutating to become tolerant to the fungicide being used.
“If you apply fungicide frequently, the pathogen develops tolerance to it.”
Bisht says the pathogen always wins over time.
“You see it happening now in canola where there’s a lot of blackleg due to tight rotations.”
“I’ve seen fields this summer where 30 to 40 percent of the canola plants have blackleg.”
Genetic resistance in canola varieties previously played the major role in blackleg suppression. But now chemical control has become necessary and blackleg is proving to be a strong opponent.
Bisht adds that improperly applied fungicides have a major impact in breaking down the effectiveness of control programs.
Fungi that survive incorrect fungicide applications, produce spores that are more resistant than the previous generation, and appear in much larger numbers. If the process repeats itself, the population of fungicide resistant organisms rapidly rises.
Agronomist Phil Needham said this type of occurrence is common.
“This summer in the central (American) plains states, we had major genetic changes with stripe rust.”
The region has wheat varieties that traditionally had been moderately resistant to stripe rust.
“The (pathogen) race changed. That’s common, but it’s hard on our plant breeders. It takes them eight to 12 years to bring out a new wheat variety.
Although the problem isn’t widespread on the Canadian Prairies yet, resistance problems are occurring more often, according to agronomist Lee Moats.
He cites the clubroot problems plaguing Alberta canola as another example. Fungicides don’t touch clubroot. Breeding resistance into new canola varieties is not a simple two-year project.
Moats says lentils are the one crop that scares him because many producers don’t check for ascochyta blight and automatically spray every year.
“We don’t risk just our own crops and our neighbours crops when we push rotations and abuse fungicides,” says Moats, a lentil grower who farms 2,650 acres at Riceton, Sask.
“We stand to sacrifice our whole lentil industry for a short-term gain. Once a variety has lost disease resistance, the only weapon we have left is fungicide. But where do we go after we wear out the fungicide?”
Vandenberg says ascochyta blight in lentils was the Prairie’s first bad experience with a pulse crop disease.
That occurred because farmers were growing lentils on lentil stubble.
“We expend a lot of effort and money on new resistant varieties. Why lose them because of bad management -short rotations and over use of fungicides?”
In the past 15 years, the Saskatchewan Pulse Growers through their grower checkoff have pumped $21 million into variety development.
Vandenberg says some producers don’t understand that money is sometimes wasted because of poor agronomy.
“Diseases keep people employed, but we’d be better off putting our efforts into developing new customers for pulse crops.”
Additional losses from lower pulse crop quality and grades also add up.
He urges growers to stick to a long rotation as it provides the greatest long-term net return to the farmer.
“In drier areas, you might get away with three years. In the dark brown soils, you need four years.”
Farmers on the Canadian Prairies may not have a long list of viable crops, but Moats says a rotation of cereal/pulse/oilseeds is practical for most farms.
In oilseeds, growers can exchange canola and flax to put a lot of years between repeating a crop. Pulse crops include peas, chickpeas and lentils. Within the cereal category, there are numerous crops, including winter wheat.
“If you look at it like that, then you’re a long way out before coming back to the same crop on the same piece of ground,” says Moats.
“The rotation system on our farm is completely independent of marketing. You figure out an agronomic system that works for your farm and let the markets take care of themselves.”
Moats has grown lentils since 1993 and has never sprayed for ascochyta blight. He has tested his seed and ascochyta has never been detected.
“So why apply fungicide?” he asks. Moats says row spacing is another
factor in preventing disease. He seeds with a Conserva Pak on 12 inch spacing, saying that the extra breathing room and air circulation help limit ascochyta.
Bisht says it’s difficult to convince a farmer to grow a different rotation when monetary returns are not good on some of the crops.
“Soybeans are finally coming into the picture, so some areas can look at that option. But for sclerotinia control, soybeans and canola are the same host.”
When a plant’s genetic resistance breaks down, fungicides serve as the backup.
In North Dakota, strobilurin fungicides have lost their ability to control ascochyta blight in chickpeas and researchers fear this tolerance is moving into lentils and peas.
In Europe, the strobilurin fungicides have lost their efficacy, especially on septoria and mildew, according to Needham.
“This is due to over use of the strobilurin chemistry.”
He says producers should use at least two modes of action in selecting fungicides.
“Fungicides really are like the magic bullet in a farmer’s arsenal. If we lose our magic bullet, it can be a bad deal for all of us.”
For more information, contact Bert Vandenberg at 306-966-8786, Vikram Bisht at 204-745-0260, Lee Moats at 306-536-8348, and Phil Needham at phil@needhamag.com.
Whether or not a fungicide application has a payback depends largely on management and expectations for the crop.
“If you grow 30 bushel wheat, the canopy isn’t dense enough to promote much disease,” said Phil Needham of Needham Ag Technologies in Calhoun, Kentucky.
He said the typical mid-range wheat crop doesn’t return enough money to justify fungicide. Such a crop is seldom limited by disease.
It has the basic yield limiting factors like moisture, nutrition, seed quality, weed control, insects or herbicide residue.
“But if you’re growing 50 or 60 bushels or maybe 90 bushels, then all the rules change. You cannot achieve those high yield potentials unless you’ve first addressed all the basic yield limiting factors.
He said fungus occurs by creating a heavy crop stand.
“So not only does the fungicide pay for itself in this situation. Now it’s become essential if you expect to get the most out of your investment.”
However preventative applications of fungicide may not pay.
“It’s very clear from looking at five years of data that indiscriminate use of fungicides does not pay, at least here in the Indian Head area,” states Indian Head Agricultural Research Foundation research manager Chris Holzapfel.
IHARF has done 20 field scale trials since 2004 on field peas, spring wheat, barley, oats, canary seed and canola.
Yield response to all fungicide products was variable on all crops in the test.
“In years when a yield response did occur, the increase in profit ranged from zero all the way up to $100 per acre,” said Holzapfel.
“However, applying fungicide every year regardless of disease pressure or environmental conditions does not appear profitable.”
Timing of the application is critical to payback, said Needham.
If the timing isn’t right, the fungicide application is wasted and it’s often necessary to anticipate the problem in advance.
Needham said it’s a little easier with early season fungicides because problems, like tan spot, can be identified before it’s time for the regular herbicide application and can be combined with that application.
Problems like Fusarium head blight require early diagnosis and specific timing for treatment.
“I had a call this morning (Aug. 17) from a farmer up near Saskatoon,” said Needham.
“With all the rain you’ve had up there, you’re getting thick, heavy stands in some areas. Perfect for Fusarium. If he had read the signs, he might have gotten in there on time with a fungicide.”
Needham said growers shouldn’t expect 100 percent control, but suppression of 40 to 50 percent is realistic.
For more information, contact Chris Holzapfel at 306-695-4200 or Phil Needham at phil@needhamag.com.
