Spraying field peas for blight might not be a paying proposition and producers should consider it carefully before spending money to combat mycosphaerella in their crops.
Agriculture Canada research scientist Syama Chatterton told those at a recent crop walk in Lethbridge that plot research in Alberta and Saskatchewan comprising 23 site years of fungicide spraying for blight has found little economic benefit.
“The three conditions that need to be met to spray for mycosphaerella blight (are), you have to see movement from the lower canopy up towards the mid and upper canopy, there should be good disease pressure, so rain or high humidity in the forecast, and peas have to be at a good economic price in order to justify the spray,” said Chatterton.
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Mycosphaerella and ascochyta blight are essentially the same disease. It is caused by a complex group of pathogens and can drastically reduce pea crop yield and quality.
“It always starts at the lower canopy and then moves upwards, and the reason why it starts at the lower canopy is because this disease is primarily stubble borne,” Chatterton said.
“If you only see it at the bottom third of your canopy, you usually don’t need to worry about it. It has to move up to where the pods are to actually cause some yield loss.”
The fungal spores can also spread on wind, in a manner similar to fusarium, and are generally present in the environment so infection is always a possibility given the right conditions.
Chatterton also does research into pea root rot. Surveys over the past two years have found the disease is prevalent in most of the province, though some areas are worse than others.
Peas have now been cropped in Alberta, usually in a four-year rotation, for about 25 years.
That means there have been five or six pea crops in the cycle and that, coupled with recent wet conditions, has allowed pea root rot pathogens to flourish.
“What we’re dealing with in this situation are two pathogens, aphanomyces root rot as well as fusarium root rot. The two of them seem to act in concert a lot and often make the disease impact worse than one alone.”
The only effective management is to avoid planting peas in fields with a history of root rot, and if aphanomyces is the causal pathogen, she recommends avoiding peas for at least six years.
Chatterton said research is underway on seed treatment applications and soil amendments that might combat root rot. However, prevention has more potential than a cure, at least at this point in the research.
