While assessing his crop for damage after a storm last year, Ian, a Manitoba producer, noticed some barley plants had white heads. Also, the kernels of the affected plants didn’t fill. Ian, who farms 1,500 acres of wheat, barley and canola near Oak Lake, Man., wasn’t sure if the storm had damaged the barley plants, or if there was another reason for the whitened heads and impaired kernel development.
It was the first week of July when I visited Ian’s farm. As I walked through the field, I noticed only a small percentage of barley heads had turned white. These plants were distributed randomly throughout the field. Of these plants, most of the barley heads hadn’t filled, and, when pulled, these heads separated easily from the stem.
Ian thought the rain, wind and hail the area received that week could have damaged the barley heads. However, the whitened and empty heads were not consistent with damage typically caused by inclement weather such as hail wounds and broken stems.
Although root rot also causes white heads, I could also rule out this type of infection because, usually, the entire plant turns white and the heads don’t pull out easily. In the case of these plants, the roots also looked healthy.
Rather, I thought the damage looked similar to what I’d seen in wheat fields, and caused by a certain pest, which burrows into the stem, killing the head.
I checked my pest guide, which indicated both wheat and barley can play host to this insect.
Crop Advisor’s Solution: Wheat stem maggot: a barley-bingeing bug
The symptoms looked like those caused by a pest I’d found in a few wheat fields that season — the wheat stem maggot.
Wheat and barley crops, as well as oats and rye, are favourable hosts of the wheat stem maggot, which burrows into the stem, consuming it and shutting off the flow of nutrients and water to the upper stem and head, thus killing them.
Wheat stem maggot larvae over-winter in the plants’ lower stems and pupate in the spring, emerging as adults in June. Once the adult flies have mated, the females lay one egg per stem on host crops, which hatch into green- or cream- coloured maggot larvae, burrow into the host stems and consume the interiors, completing the cycle.
Cultural control methods are recommended when managing wheat stem maggot infestations. For example, include non-host crops in the rotation, destroy infested stubble, control volunteer plants, and delay planting.
Because only a small percentage of plants were affected in Ian’s barley field, the yield loss at harvest was almost negligible.
Kathy-Jo Toews works for Richardson Pioneer Ltd. in Brandon, Man.