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Crop advisor casebook: Wheat heads not your typical yellow fellows

A Crop Advisor's Solution from the December 3, 2019 issue of Grainews

As the wheat matured, some of the wheat heads weren’t turning the typical bright yellow but instead were much darker in colour and had striped kernels.
Naomi Darragh. photo: Supplied

Back in mid-August, I got a call from Jay after he noticed something wasn’t right with his wheat crop.

Jay, who is a grain producer in the Provost region, had just finished scouting one of his fields planted to CWRS wheat. He was alarmed to see that as his wheat matured, some of the wheat heads weren’t turning the typical bright yellow but instead were much darker in colour and had striped kernels.

I wanted to have a look at the plant symptoms myself, so I made my way out to Jay’s farm.

When I arrived at the field and surveyed the crop, my first impression was it had a dull appearance similar to wheat that had stood through a couple of heavy rains, and I thought it might have some mould on it. As I walked through the field, I could clearly see blotches and stripes on the glumes of affected wheat heads that were dark brown to dark purple in colour.

Jay told me he hadn’t seen symptoms like this in his wheat before and asked if I knew what might have caused the symptoms.

I had my suspicions, but first I needed to rule a few things out. I was informed by Jay that the field had been planted with treated seed, but there were no foliar fungicides applied in-season. There had also been a number of herbicide applications, which achieved good weed control. I inquired about Jay’s nutrient applications on the field, and based on soil tests and field history, he appeared to have a good fertility plan in place.

When I inquired about what kind of weather patterns Jay had noticed throughout the summer, he mentioned there had been above average rainfall and during the flowering and grain-fill periods, the temperatures were consistently in the mid-20s.

At this point, I had a good idea what was behind the injury in Jay’s wheat field.

Crop Advisor’s Solution: Glume blotch ailing Jay’s wheat crop

I knew then the most likely culprit was glume blotch — a cereal disease caused by septoria infections that thrives in moist and humid growing conditions and with temperatures ranging between 20 and 28 C.

I double-checked my disease resources and found the injury pattern and symptoms in Jay’s wheat matched the description for glume blotch. I also consulted a local plant pathologist who agreed with my diagnosis.

At this point in the season, there wasn’t anything Jay could do about the disease symptoms in his wheat crop. The disease caused a slight drop in yield, and the crop was downgraded due to the presence of both glume blotch and fusarium head blight. The two are similar; however, the glume blotch pathogen doesn’t produce mycotoxins, unlike fusarium.

In future cropping seasons, Jay will keep a closer eye out for glume blotch and other leaf diseases in his wheat fields prior to the flag leaf stage through to flowering, and he will apply foliar fungicides when necessary. For wheat producers like Jay, there are a number of other measures they can take to help protect their fields from glume blotch. These measures include implementing at least a three-year crop rotation with pulses and oilseeds, utilizing resistant cultivars, planting disease-free seed, wider row spacing, and ensuring a balanced fertility program to avoid canopy conditions that favour disease infection.

Naomi Darragh, PAg, CCA, is an agronomist with Richardson Pioneer Ltd. in Provost, Alta.

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