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Barley leaf diseases stealing yield

Spot blotch, net blotch will join fusarium head blight as problems in Sask. and Alta.

Fusarium head blight (FHB) is the most high-profile of the diseases that threaten wheat and barley annually across the Prairies. But researchers say foliar diseases will likely be the biggest barley “yield culprits” in Alberta and Saskatchewan in 2016.

“From a regional perspective, leaf diseases tend to be Prairie-wide and are habitually something producers should be concerned about, especially in continuous barley or where you have a single year between barley crops,” says Kelly Turkington, a research scientist with Agriculture and Agri-Food Canada.

In some areas of Alberta and Saskatchewan, Turkington says, 50 to 60 per cent of growers allow just a single year between cereals in the rotation. Short rotations mean net blotch diseases — like net-form net blotch and spot-form net blotch — can gain a foothold in crop residues.

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All of the leaf diseases of note — net blotches, spot blotch and scald — can be transmitted through the seed, but crop residue is generally the culprit in short rotations.

Scald is always a concern in cooler regions of Alberta and northern Saskatchewan. But spot blotch (as distinguished from spot-form net blotch) is also becoming an issue for growers in those provinces. “Spot blotch is a different animal than net blotch — it’s the same fungus that causes root rot, seedling blight and kernel smudge, and it’s been more of an issue in the eastern prairies,” he says. “But we’re seeing more of it in Alberta now, while it is one of the more dominant leaf diseases in Manitoba and Saskatchewan.”

Some variety guides, including Alberta’s, omit spot blotch ratings, but Turkington says his team intends to propose its inclusion for the 2017 Alberta guide.

In Manitoba, 2015 saw fewer occurrences of leaf diseases than the other Prairie provinces, according to Xiben Wang, a pathologist at AAFC’s Cereal Research Centre in Morden, Man.

“Leaf spots were normal. Cochliobolus sativus, the causal agent of spot blotch, and Pyrenophora teres, the causal agent of net blotch, were the principal pathogens — I would assume because farmers are spraying a lot of fungicide, so disease pressure overall was a bit lighter than normal in 2015,” he says.

Manitoba growers will likely face FHB as the chief disease in 2016. Wang says their best defense is the use of resistant varieties, proper crop rotations and staying on top of timely fungicide applications.

Scouting for leaf diseases

Turkington says the best time to scout for leaf diseases is at the seedling stage, but unlike with FHB, control can happen well after symptoms are noted in the field.

“The nice thing with leaf diseases is that you can follow them through the growing season. It’s not the same as FHB, where you have to make the call before you see symptoms,” he says. “With leaf diseases, you can note the presence of the diseases and then go back out.”

For spot-form net blotch and spot blotch, growers should look for small brown spots on barley leaves. Higher severity will appear in the lower leaves, with severity decreasing toward the upper part of the canopy. “As the symptoms become more mature and severe, you’ll see yellowing around the lesions,” he says.

Spot blotch can be distinguished from net-form net blotch by the shape of the lesions: spot blotch lesions are larger and oval-shaped, whereas net-form net blotch lesions elongate, following the veins, with necrosis or browning between them. Unfortunately, Turkington says, symptoms of spot blotch and spot-form net blotch can be quite similar.

Scald, on the other hand, will first appear as “water soaked spots” in oval, eye-shaped lesions on the leaves. “If you take a healthy leaf and crunch it up, the damaged tissue takes on a more intense green, a ‘wet’ look,” says Turkington. The dead tissue will eventually turn tan-coloured with dark purple-black margins.

Turkington says the research suggests that fungicide should not be used on barley until flag leaf emergence or anthesis. Herbicide timing is not recommended.

“My rule of thumb is to look at around flag leaf emergence — look at the lower canopy. Do you see signs of disease? And it has to be actual symptoms, not leaf yellowing due to heat stress or nitrogen deficiency,” he says.

“Look at the third leaf down from the head, and look at 50 to 100 leaves in several locations, and if you’re not seeing any disease, or on average less than one to two per cent of the leaf area is affected, chances are you don’t have a huge issue developing,” he says. “If you do see one to two per cent, I would re-evaluate as the crop is coming into head emergence, and then hit it with a fungicide if you see a problem.”

Barley varieties with a good or very good resistance rating to leaf diseases will likely withstand disease pressure. “You’re better off relying on the resistance as your key disease management strategy, especially if it has the disease package required and meets your on-farm or marketing needs,” Turkington says.

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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