Crop advisor casebook: Patchy problems in a canola field

A Crop Advisor's Solution from the September 25, 2018 issue of Grainews

Plant density was low in some areas. The plants in these patchy regions were also much smaller than those in the rest of the field.
Samantha Marcino. photo: Supplied

On June 11, while spraying his canola plants with an in-crop herbicide, Wade noticed regions of the crop had uneven emergence, causing some patchy areas.

Wade farms 10,000 acres of canola, wheat and barley near Yorkton, Sask. He thought he might have an insect problem in his canola crop. “My guess is it’s flea beetles or cutworms,” he said.

Wade asked me to make a trip out to his farm to help diagnose the issue. When I arrived, we scouted the canola fields. Only one field was exhibiting symptoms.

In that field, plant density was low in some areas. The plants in these patchy regions were also much smaller than those in the rest of the field. Some plants appeared to have just emerged.

Additionally, there was a distinct pattern to the damage — the affected areas all occurred within one big region. Within that region, some rows were more affected than others. The rest of the stand had larger plants, which also appeared healthy.

Wade thought the damage could be caused by pest pressure. Cutworms cause chewing damage, such as holes and notches, to leaves. They also cut stems below the soil surface, so plants are found lying on the ground, or they look like they’ve been knocked over.

There were no signs of leaf-chewing damage. photo: Supplied

Cutworms create patches in fields. These areas are randomly distributed, usually expanding outward from a point of origin as the insects continue to eat more plants.

When we examined the field for cutworm pressure, we didn’t find any evidence of activity consistent with cutworm damage. For example, there were no cutworms, severed plants or notched leaves.

At that time, we also looked for leaf-chewing damage caused by flea beetles, such as notches or circular pits on leaves. Again, there was no signs of excessive flea beetle feeding on the plants in these areas or the field.

With the dry conditions farmers experienced this past spring, fertilizer burn had to be considered. In general, producers must be cautious when using seed-placed fertilizer with canola seed because the seed can be easily injured. Too much fertilizer placed with the seed reduces the germination rate.

If the seeds were injured due to fertilizer burn, I would expect to find that they hadn’t sprouted in the affected areas. When I dug into the soil, I found germinated seeds; thus, fertilizer burn wasn’t to blame. However, while inspecting for fertilizer burn, I discovered the reason for the poor emergence and thin plant stand in the damaged areas.

Crop Advisor’s Solution: Keep checking your depth setting when seeding canola

When we dug into the soil, we found the seeds had germinated, but they were seeded more than two inches deep — much too deep for canola. I found many seed shells from germinated seeds, but the seeds didn’t have enough strength to get to the soil surface to produce viable plants.

The patches occurred in one specific region of one field. This was clearly a seeding malfunction, as Wade didn’t purposely seed the canola that deep. He probably had a few shanks sink slightly deeper into the ground in the affected areas of the field. Perhaps a setting was off as he moved from one field to the field in question, and one section of the drill was sinking in deeper than the others.

Although Wade didn’t detect the problem until early June, enough canola came up in the affected areas to make a crop. However, those areas were significantly delayed when compared with the rest of the crop. This issue also made herbicide and fungicide staging more difficult because of the uneven plant development.

With canola, a rapid, even germination, which produces a uniform plant stand, is desired. Seeding depths from 0.5 to one inch produce the highest emergence rates and the most uniform plant stands.

It’s vital to set the seeding depth correctly — and to keep checking that depth setting throughout seeding to ensure it hasn’t changed.

Had the crop been a cereal, this issue wouldn’t have been such a concern. Seeding depth is important when planting canola because the seed is so tiny and it only has so much strength and energy to make it out of the ground.

Samantha Marcino works for Richardson Pioneer Ltd. in Yorkton, Sask.

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