June winds add to risk of bacterial blight

Some bean, oat, pea crops in Manitoba showing bacterial infections

Mature lesions caused by common bacterial blight in dry beans.

Glacier FarmMedia – Add bacterial blight to the problems Manitoba producers are fighting this year.

Agronomists have noted blight issues in a number of crops, such as oats, dry beans, and some concern in peas, according to provincial crop pathologist David Kaminski.

High winds in June did little to help mitigate bacterial blight risk. Parts of the province saw wind gusts over 100 km/h June 11, with several other days in June clocking wind gusts near or above 70 km/h.

"I don't know if we can attribute everything to the wind," Kaminski said, though he noted high wind, by picking up soil and blasting plants, results in wounds that pave the way for bacteria to infect a plant.

"Otherwise, bacteria have to get into the plant through natural openings like stomata," he said.

Bacterial blight in oats is a problem year-after-year, he noted. They have not noted issues as widespread in peas, he said, but added that, given a general rise in pea acres this year, there is increased scrutiny on the crop in general.

Outside of wind damage, Kaminski said some issues might be seed-borne, particularly in non-certified, carried-over seed, while variety susceptibility or rotation issues may be other contributing factors. Nearby oat stubble, for instance, can be a vector for bacterial blight, he noted.

"With the pulses I don't think it's as common, but oats is quite common. There's always a good chance that you're on or near oat stubble as an early source of infection," he said.

Producers might also have courted blight spread if dry beans were cultivated while leaves were wet, provincial pulse specialists told attendees of a provincial Crop Talk webinar June 23.

"Right now, the plants are still quite small, so the risk is quite low for spread that way, because you're not really touching the plants, but if you're cultivating later in the season and there's some bacterial blight, you want to be careful not to cultivate when the leaves are wet," pulse specialist Dennis Lange said during the webinar.

Hard to hone in on yield impact

It's difficult to say how much those blight issues might come due at the bin, Kaminski noted.

In many cases, blight symptoms are noted early in the season, while the crop seems to grow out of the problem as the year goes on.

"That's especially true in the cereals," he said.

Eyes are typically drawn to damaged parts of the leaf, leading many to overestimate exactly how much of the flag leaf, so critical for head-fill, is actually lost, Kaminski had told webinar attendees earlier.

Australia plant pathologist Dr. Mark McLean shows symptoms of bacterial blight in an oat crop. photo: ExtensionAUS video screengrab via YouTube

Make the ID

Some producers may be wasting time and money spraying a problem that won't be fixed with fungicide, Kaminski noted.

"Get it to a lab as soon as possible," he said.

The Crop Diagnostic Centre in Winnipeg is "as good a place as any to start," he added.

"They would be able to tell you in fairly quick time," he said. "If it turns out to be a fungal disease and fungicides are an option, most of the timing for fungicides is at early flowering or later, because the pathogens, or the disease, can't do too much in terms of yield until it gets onto the developing pods, and then it can be a real issue. So you want to have the fungicide there if you have disease developing before any of the pods are beginning to form."

Kaminski says he is fielding pathogen identification questions from producers noting symptoms on the lower leaves of their pea plants.

In the most recent Bean Report published by Manitoba Pulse and Soybean Growers, the grower group noted that pea producers risk misdiagnosing bacterial blight with mycosphaerella (ascochyta) blight, which, unlike bacterial infections, can be treated with foliar fungicide.

Treatment

For fields that do come back with bacterial blight, producers have few in-season options.

Dry bean producers may turn to copper fungicides to slow halo blight, although the province warns that such products have to be applied repeatedly, early in the season, and are only moderately effective.

There are some peroxide-based products registered for dry beans, although Kaminksi noted that those labels do not extend to crops like peas.

Likewise, he cautioned, those products are more protectant than treatment, and producers turning to them to prevent a problem will likely have to reapply multiple times.

"They may stop the disease where it is, but they won't necessarily protect any new growth," Kaminski said.

Studies on the efficacy of such products out of the University of Guelph showed little difference in leaf damage or yield between treated plots and an inoculated control, Crop Talk attendees heard June 23 and, while similar research out of North Dakota State University did see some benefit to foliage, that benefit similarly did not transfer to greater yield.

Alexis Stockford is a reporter with the Manitoba Co-operator. Her article appeared in the June 24, 2021 issue.

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