Tuesday, 28 June 2011 15:05

Crop diseases which hurt farmers last year: they’re back

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By Jamie Woodford
Crop disease is a serious issue, and last year’s growing season in southern Alberta saw a lot of it.

Although a hot, dry summer is predicted, this year’s crop could face the same fate should the wet weather continue.

Ron Howard, plant pathology research scientist with Alberta Agriculture said 2011 is already following the same path as last season.

“We are seeing a very similar scenario to last year with the development of early season diseases favoured by moisture,” he said.

“The long range forecast is for a drier summer this year compared to last year, which we would hope would reduce disease, but so far, it’s starting out almost the same.”

Howard said with pathogens able to survive in 2010’s crop residues the likelihood of disease reoccurring is high.

There are three factors which create good infectious disease development, he said.

First, is a susceptible plant. Second, is the presence of a pathogen, and third, is a favourable environment.

“We call that the disease triangle: host, pathogen, environment. Last year, those coincided.”

Howard said the only factor that could change the course of disease popping up this year is the weather.

“If we get a repeat of the 2010 weather patterns you can expect to see the same diseases coming back at the same, maybe even higher, levels,” he said. “That’s what happened so far this spring is the early onset of these disease. That could change if we get a warm, dry summer, but if the patterns continue and they duplicate 2010, we know that we’re in for a battle.”

In 2010, the leading diseases in wheat were tan spot, spot blotch and victoria leaf blotch. In barley, spot blotch, net blotch and scald were common.

Fusarium Head Bight is another familiar disease in cereal crops. Southern Alberta is an especially high risk area for the fungal disease.

“We see the worst levels of Fusarium Head Bight under irrigation in the Medicine Hat to Lethbridge area,” Howard said.

“This disease infects the heads as spores. You have to have conditions of high humidity, or rain or irrigation water entering the picture at the time of flowering when ... they’re open to the spores depositing inside and infecting the developing kernel.”

Some disease in 2010 occurred well before seeds were able to germinate.

Seedling blight, when seeds germinate, rise above the ground and die, is usually caused by soil borne fungal pathogens or too much moisture, said Howard.

“Years like this where we get higher than normal levels of precipitation and flooding, then we worry about seed not germinating or if it does germinate, the seedling is dying because of too much water in the soil, or activity of seed borne decay organisms,” he explained.

Prevention is key to reducing the impacts of disease.

“With diseases the emphasis is definitely on prevention,” said

Howard. “We don’t have an arsenal of therapeutic products that will control established infections in plants the same way we do it in people or animals.”

Howard recommends three key strategies to prevent disease: field history, vigourous varieties and a management plan that includes fungicide and irrigation strategies to reduce the impact of disease.

“Growers need to know the disease history of their fields and prepare a control strategy based on those diseases,” he noted.

Howard strongly advocates producers to scout their fields on a regular basis, or have a certified crop advisor do it.

“This helps them to anticipate disease while they’re in the early stages and

it may be possible to do something.

Once the diseases get established and virtually out of control, there’s often not much that can be done.”

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