As wheat crops across Ontario break dormancy and get growing in earnest, farmers and agronomists need to be on alert for symptoms of micronutrient deficiencies — particularly manganese. On this week’s Agronomic Monday edition of RealAg Radio, Peter “Wheat Pete” Johnson dug deep into why manganese matters, why timing is critical when correcting a deficiency, and why this sometimes-tricky nutrient demands respect.
“Wheat can look great one moment and be struggling the next,” says Johnson, “especially when manganese is in short supply.” While not as widely discussed as nitrogen or phosphorus, manganese plays a critical role in photosynthesis and enzyme systems in wheat. A deficiency, if left unchecked, can dramatically impact tiller development and ultimately yield potential.
It’s important to understand that manganese doesn’t move within the plant. “If you foliar-apply manganese to the lower leaves, it’s stuck there. It won’t transfer to new growth,” Johnson explains.
This immobility limits how “proactive” farmers can be with manganese. Applying it before symptoms appear might seem like a smart hedge, but it’s often wasteful and ineffective. “If your wheat isn’t showing symptoms, and there’s no history of deficiency in that area, don’t just spray it,” he says.
Some growers may choose to tank-mix manganese with herbicides or fungicides; however, this can cause an issue. “You can get antagonism,” Johnson says. “Especially if you’re using dry manganese sulphate at higher rates, mixing it with other products can really backfire.” Instead, growers should monitor closely and respond immediately when deficiency signs — such as interveinal chlorosis on upper leaves — show up.
Growers hoping to rely on soil tests to predict manganese issues may be in for a rude awakening. Unlike many other nutrients, manganese availability is heavily influenced by soil moisture, pH, and organic matter.
“In wet conditions, manganese is available. In dry areas, it becomes locked up,” Johnson notes. “Soil tests are incredibly variable and not reliable for manganese. You really need historical context and in-season scouting.”
This means that what works in one part of the field — or one year — may not work the next. One listener, Ryan, saw the consequences of delay firsthand. After spotting manganese deficiency in the fall, he was advised to wait until spring to correct it. “That was a mistake,” says Johnson. “The growth difference is dramatic now. You can’t make up for lost time with manganese.”
It’s a lesson that reinforces Johnson’s golden rule: when you see a manganese deficiency, treat it immediately.
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