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Diagnosing herbicide injury

Application can go wrong. Know how to limit and recognize herbicide injury

Group 2 (Odyssey) injuries in canola on display at CanoLAB 17 in Vermilion. Staff mimicked a drift injury in the greenhouse. Herbicide injury symptoms, 
such as purpling and thickened stems, can mimic other issues. Photo: Lisa Guenther

When it comes to diagnosing potential herbicide injury, record keeping is vital, say Canola Council of Canada agronomists.

“With soil residual herbicides, herbicide history is really important,” says Ian Epp, agronomy specialist with the Council for northwestern Saskatchewan. Because soil residual herbicides are often applied the previous year, good record keeping is important, he adds.

Last year’s herbicide rotation can limit next year’s crop choices, Epp says. With good record-keeping “you can solve a lot of these problems before they even happen.”

Brittany Hennig, agronomy specialist for southern Alberta, says farmers who suspect herbicide damage should also look at recent weather conditions, nutrients and insects to rule out damage from those quarters. For example, purpling is a symptom of possible herbicide injury. But it can also indicate nutrient deficiency, or an extreme temperature change, Hennig says.

Residual herbicide damage

There are herbicides within Groups 2, 4, 5 and 14 that can affect next year’s canola crop, according to the Canola Council’s booklet on diagnosing herbicide residue and drift injury. But not every herbicide within those groups affects canola, the booklet notes, so farmers should check labels.

“We see more Group 14s, which can have some residual activity,” says Epp. More pulse acres also mean more Group 2s being used, which have soil-active properties, Epp adds. Combine that with a dry spring, and farmers can end up with soil residual herbicide injury.

Spraying one product too often in one season can restrict cropping options the next year, Hennig says. And it’s important to pay close attention to labels, she says. “There are just a lot of details and a lot of different actions between the groups as well.”

Epp says soil residual herbicide injury can be tough to diagnose.

“The plants are small, and sometimes plants don’t germinate. It’s more of a lack of symptoms that you’re trying to diagnose as opposed to bigger plants that show all sorts of symptoms, depending on what herbicide it is.”

Along with examining field history, producers can look for patches in the field, Epp says. Sometimes a lack of emergence looks like stand establishment issues. Rule out seeding rate, seeding depth, and moisture issues in the spring. With some soil-residual herbicides, soil organic matter, pH, and temperature can be factors, he adds.

Herbicide injury symptoms also include early season purpling, yellowing, and stunted growth. But those symptoms can also be caused by other problems. Group 2s can cause root pruning, but that can be hard to diagnose, as it can also be caused by seedling disease or cutworm issues. Symptoms can also be relative, Epp says, depending on the field and variety.

Epp recommends gathering several plants, including good, sick and “some really ugly-looking ones.” Farmers and agronomists can then line up the plants on the tailgate to compare and to photograph.

Photographs of seedlings with potential herbicide injury are also helpful, in case agronomists aren’t able to evaluate the plants when the symptoms are most visible. Epp recommends taking as many photos as possible.

Herbicide drift

As for farmers who suspect herbicide drift or a contaminated sprayer, Hennig suggests looking for patterns within the field. “It’s very similar to seeing if there’s a plugged nozzle.”

When it comes to spray tank contamination, the crop injury tends to depend on what part of the sprayer was contaminated. The Canola Council’s herbicide injury booklet states that residue in the boom and spray jets might dissipate after a few passes. In that case, the injury should match the application, the Council states. But a contaminated tank, sump, or filter can affect a larger area.

Farmers looking for herbicide drift injury should scout along the field edges, Hennig says. The Canola Council notes that although drift injury is usually on the field edge or near shelterbelts, herbicides such as 2,4-D ester can drift further into the field.

Herbicide injury is serious, and not something a farmer should assume the crop will grow out of, Hennig says. But a farmer shouldn’t assume the crop has been destroyed, either.

“Look at everything and see if growing points are still intact. Is there a chance for your canola crop to still survive?”

Hennig recommends farmers call in an agronomist anytime they’re unsure what’s going on, rather than hoping the crop will be okay. “If you want a second opinion, definitely give us a shout.”

Farmers unsure about cropping restrictions or spraying a certain chemical can always call the agronomist beforehand. It’s also worth being proactive rather than reactive about calling in an agronomist, Hennig says.

”Stick to the label as much as possible because although your neighbour might have done it and gotten away with it, that doesn’t mean that you’re going to get away with it.”

Get more information

A booklet on this issue, “Recognizing Herbicide Residue and Drift Injury in Canola” is available from the Canola Council. To find it online, visit Contact information for Canola Council staff is also available on the website.

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