Crop advisor casebook: What’s causing these wheat heads to curl?

A Crop Advisor's Solution from the July 17, 2018 issue of Grainews

Crop advisor casebook: What’s causing these wheat heads to curl?
Allison Attema. photo: Supplied

John, who owns a mixed grain farm near Lacombe, Alta., called me last July after he discovered curled and deformed wheat heads in his crop. He said the affected plants were scattered throughout the field, and approximately 10 per cent of the crop was affected.

At the field, examination of the plants revealed healthy and normal development, however, a small percentage had curled or deformed wheat heads.

Many factors can cause this deformity, such as herbicides, insects or environmental forces. Regardless of the cause, this type of damage to the head often occurs when it is coming out of the boot.

For example, incorrect herbicide timing can cause the flag leaf to become twisted. Awns become trapped in the damaged flag leaf, causing head deformity. In addition, herbicide drift from a neighbouring field can also cause injury to the developing heads.

However, we easily ruled out chemical drift as the wheat field was surrounded by pastureland that hadn’t been sprayed with any herbicides. Injury due to incorrect herbicide spray timing could also be eliminated because John’s application rate and timing were spot on. Additionally, in general, the plants looked healthy and were developing normally, and didn’t present symptoms typical of herbicide injury.

There are also a few insects that can make wheat heads curl. The wheat curl mite and the Russian wheat aphid can cause a plant’s flag leaf to curl, trapping the awns and causing the head to distort when the awns emerge from the boot.

Once again, this theory could be easily eliminated as the flag leaves of the affected plants were not curled.

To determine if the damage originated from an environmental source, we examined the affected plants once again. Sure enough, we found a few minor wounds on some of the plants’ stems. I now had a diagnosis for John.

Crop Advisor’s Solution: Hail no! A storm robbed this farmer’s field

Because the herbicide spray timing and application rate were correct, and pastureland that was free of any herbicide applications surrounded this field, we could also rule out herbicide injury as the cause of the deformed wheat heads.

This left us with injury from an environmental factor. A closer look at all the affected plants revealed slight wounds on stems and some minor tears in the leaves. With this evidence, John and I checked weather reports for the weeks preceding the discovery of damage.

A few storms had passed through the region, and a hail event occurred during the crop’s boot stage — the plants had been injured by hail!

While severe hail damage is easy to identify, lighter storms during certain plant developmental stages can cause symptoms that appear long after the storm has moved through the area. Hail or wind damage can rip the plant’s boot or flag leaf, and the awns catch as the wheat head is emerging, which causes the head to look deformed or curled.

Unfortunately, there’s nothing a producer can do to prevent hail damage. However, the damage to John’s crop earlier in the season didn’t appear to affect yield at harvest.

The bruise on this stem offered a clue that hail was likely responsible for the damaged wheat plant. photo: Supplied

Allison Attema works for Richardson Pioneer Ltd. in Lacombe, Alta.

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