Saskatchewan irrigators can consider themselves warned: look out for bacterial leaf streak.
Gursahib Singh, research director of the Irrigation Crop Diversification Corp. (ICDC), presented to 200 members of the irrigation industry at the Irrigation Saskatchewan conference on Dec. 5 in Saskatoon.
Bacterial leaf streak is so far not a problem in Saskatchewan, but has been a growing problem in Alberta and the U.S. for the last decade.
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The air- and seed-borne pathogen is mostly seen in irrigated crops, with no management practices or crop resistance available for Canadian cereals. Bactericides, copper and seed treatments do not have an effect, said Singh, who offered up the warning while outlining over 50 other research projects going on at ICDC.
Leaf streak often gets misdiagnosed and when farmers see it as a fungal infection, reaching for the fungicide isn’t going to help, he said.
“You are killing all the other saprophytes or other pathogens, and there is no competition left. You’re not killing bacteria, they’re the pathogen that is left and you are giving them every opportunity to invade the leaves or the crop.”
This increase in cases is fairly new, so Saskatchewan researchers are yet to start any extensive research, Singh said, but they are learning from researchers in Alberta and the U.S.
Singh said he and professor Randy Kutcher at the University of Saskatchewan are watching to see whether the problem crosses into the province.
Thomas Kelly Turkington, plant pathologist with the Agriculture and Agri-Food Canada Research and Development Centre at Lacombe, and Michael Harding, crop health assurance lead for Alberta Agriculture and Irrigation, are the leading experts on the disease in Alberta, Singh noted.
Minor cases of bacterial leaf streak have been recorded on the Prairies since 1920, but never as severe as what they are seeing right now, Harding said.
Strong annual increases of the disease have created economic losses in the U.S. Midwest and Plains since around 2012 and for southern Alberta irrigators starting in 2015, he said.
Three factors have to be ideal for the disease to thrive, he said. The pathogen must be present, with a susceptible host and the perfect weather conditions, and the potential is there for the problem to continue growing.
“Depending on those three sides of the disease triangle, that’s really going to determine what happens, but based on what we’ve seen happen in North America so far, it wouldn’t be that surprising if the disease became more prevalent and more severe in more fields across the Prairies.”
All wheat and barley crops grown on the Prairies are “extremely or fairly susceptible,” he said, but drought conditions have slowed the spread of disease. However, irrigation creates the proper moisture conditions for both growth and spread of the disease in these grass and cereal crops.
Spreading information on the signs of infection has been important for the Alberta irrigation community.
When seeing spots on leaves during scouting, most farmers diagnose the problem as cereal leaf spot, and more often they’re correct. This is why misdiagnoses are prevalent: farmers just don’t expect the leaf streak to be in their field.
Telltale signs of bacterial leaf streak include a lesion on the third leaf down the midrib turning from yellow to a heavy bacterial ooze and black chafe on the head.
Letting the canopy dry between irrigation events can help slow the spread of the disease — but crops need water, Harding said, so if it’s a toss-up between spreading the disease and ensuring adequate water, growers are going to lose more yields from the latter than the former.
The best management practice farmers have in their toolbox right now is proper crop rotations, he said.
“If you can get a hold of seed that has little or non-detectable levels of bacteria, and you’ve got a two- to three-year break between cereal crops, you’re probably going to be breaking the cycle enough that this isn’t going to be a consistent problem.”
Even though no specific cultivar has built up any resistance or tolerance to the disease, the search has already begun to identify strains with which breeders can work, Harding said.
“We don’t really have a good answer for what cultivars have higher tolerance to this or what are more susceptible…that work has started and we will over time have those answers.”
– Becky Zimmer is a freelance journalist at Humboldt, Sask.
