Fungicide season has begun

Flag leaf stage applications provide the best protection

Winter wheat is at, or near the stage, for applying fungicides to protect it from various leaf diseases and spring wheat isn’t far behind, says Holly Derksen, a plant pathologist with Manitoba Agriculture, Food and Rural Initiatives (MAFRI).

Some winter wheat fields were at the flag-leaf stage last week and more will be this week, she said. Farmers trying to protect both winter and spring wheat should apply fungicides at the flag-leaf stage to get the best protection against leaf rust.

Spraying to prevent stem rust should begin at the first sign of disease until the end of the flowering, according to MAFRI’s 2012 Guide to Field Crop Protection.

“Rusts across the West have been showing up two weeks earlier than in a normal year, but crops are also two weeks ahead of where they are in a normal year,” Derksen said. “I’ve had one report of rust near the Dauphin area… It’s unknown if it came in on a wind event or if it overwintered.”

The cooler weather that followed that initial finding slowed the disease down, she added.

Some farmers spray their wheat with a half-rate of fungicide when applying herbicides. Derksen said she normally doesn’t recommend it because diseases aren’t usually a problem that early in the season.

“I want growers to consider rotation and consider your risk management — if you’re willing to put on that extra application cost, but also consider resistance management,” she said. “Is an additional application of fungicide going to limit you later this season, and if not this season, is it going to limit what fungicides are available to you in the future? Resistance is showing up in pathogens and I want to make sure growers are aware of it.”

The early half-rate is something to consider if disease is showing up early or if it’s a high-risk situation, such as wheat planted on wheat stubble, Derksen added.

It won’t be long until farmers will be deciding whether to apply fungicides to protect their wheat against fusarium head blight, a fungal disease that cuts yields and quality.

The first line of defence is variety selection. While no wheat is resistant, some are less susceptible. Planting a less susceptible variety, in combination with agronomic practices and fungicides, is the best approach.

Some years winter wheat flowers early enough to avoid the disease, but if the inoculum is present and the weather is right, winter wheat is susceptible.

Fusarium head blight is most likely to develop when temperatures range from 15 to 30 C and high moisture is continuous for 48 to 60 hours. If conditions remain warm and moist, the pathogen can continue to sporulate and spread to other kernels or heads, the crop protection guide says.

“Under these optimum conditions, crop management has little impact on FHB outbreaks.”

Practices that reduce tillering and shorten flowering can reduce the risk period for fusarium infection. They also help fungicides to be more effective.

A number of fungicides, including Folicur, Caramba, Proline and Prosaro, are registered for “suppression” of fusarium head blight in wheat.

All are Group 3 fungicides and all recommend the same timing for application — when at least 75 per cent of the heads are fully emerged to when 50 per cent of the heads on the main stem are in flower.

The crop protection guide says spray equipment must be set to provide good coverage to heads (e.g. forward- and backward-mounted nozzles, or nozzles that have a two-directional spray).

About the author

Reporter

Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.

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