John, who farms 2,000 acres of wheat northeast of Medicine Hat, Alta., changed things up a bit
last spring by planting 400 acres of canola for the first time. Things were going well until he suddenly noticed a large number of plants, about 30 to 40 acres, were disappearing from hilltops, hillsides and drier areas of his field as they were starting to cabbage out in mid-June. Since this was his first time growing canola, John had a lot of questions about the damage to his canola stand, but he also had his own theory: “I’ve got a lot of damage on the hillsides, it looks like cutworms to me,” said John.
Later that evening, I examined John’s field—the hillsides were patchy with some areas completely empty of canola plants, it looked like his stand was disappearing. The plants appeared to be eaten and chewed off at the base of the stem. Only the very bottom of the plant remained. Small pieces of stem were found in the soil and above its surface. Cutworms often destroy hilltops
and south-facing slopes first, so John’s theory seemed sound. Evening is the best time to scout for cutworms—as this is the time when they are actively feeding—so we decided to examine the soil and plant leaves for their presence. Cutworms sever plant stems below the soil’s surface as well as feed on the leaves.
We carefully examined the plants for feeding larvae and found none. We then dug in the soil looking for the long, grayish-green larvae—but, again, found nothing. Also, we expected to see plant stems severed below the soil surface by the cutworms, but below the soil the plant was intact.
Plants began disappearing from hilltops and hillsides, but were chewed above ground
The plants looked nipped off right at ground level—not typical evidence of cutworm activity. All evidence suggested cutworms were not causing John’s canola plants to disappear.
Because other areas of John’s canola field had healthy plants we were able to eliminate some of the conditions that could account for the bald patches on the hillsides, such as fertilizer application rate, seeding depth and germination rate. John wondered if the extreme amount of precipitation that spring could have caused the damage he was now experiencing in mid-June. Although soil erosion caused by large amounts of water could create some bald patches the plants would not look neatly nipped off at the stems. Clearly, we were looking for something eating the plants, but what?
What is plaguing the canola plants in John’s field? Send your diagnosis to GRAINEWS, Box 9800, Winnipeg, MB, R3C 3K7; e-mail [email protected] or fax 204- 944-5416 c/o Crop Advisor’s Casebook. Best suggestions will be pooled and one winner will be drawn for a chance to win a GRAINEWS cap and a one-year subscription to the magazine. The reasoning which solved the mystery will appear in the next Crop Advisor’s Solution File.
KeithLeveeisacropinputmanager atRichardsonPioneerLtd.atMedicine Hat,Alta.