Although farmers are hardly ever thrown by the surprises they sometimes find in their fields, John, who farms southwest of Shoal Lake, Man., was perplexed about the large, bare patches he found in his flax field while on a routine scout.
John produces canola, flax, barley and wheat on his 2,500- acre farm. He thought the over-moist soil had rotted his seed causing the bare patches. “It’s been really wet lately and I think over-saturation has caused my seed to rot,” he explained over the telephone.
The next day, as we approached John’s flax field I could see large, irregular, bare patches surrounded by emerged, healthy plants approximately five centimeters tall. On closer inspection I found the bald spots were mainly located on hilltops and drier areas.
I thought the serious contenders for the cause of the destruction in John’s field could be seed rot due to excessive moisture, fertilizer application rate or seeding depth. But none of these issues turned out to be the cause of John’s spotty field.
We found seed coats in the rows as well as flax seedlings when we checked in the soil, so the bare patches were not caused by poor germination rate or slow-to-emerge plants due to very deep seeding. Also, the seed did not appear to be burned by fertilizer and according to John’s records, his rate of fertilizer application was spot on.
Upon close examination of the flax seedlings we found our first clue to solving the cause of the destruction in John’s field. The seedling appeared to be chewed off near the base of the stem. We carefully searched the surrounding area and found two long, grayish-green larvae. I knew immediately what they were — pale western cutworms.
The larvae of cutworms sever plant stems below the surface of the soil, but can also feed on leaves above the soil. When cutworms are present in a field they often start destroying hilltops and south-facing slopes first and usually move down plant rows leaving bare patches in their wake.
In order to stop the cutworms from causing any more damage to John’s field an insecticide was applied late in the evening — it is important to spray in the evening when the larvae are actively feeding — to kill the cutworms. We applied the insecticide to the bare patches only.
It is impossible to prevent cutworms from invading your fields, but loss can be lessened by catching the problem early through regular scouting of your fields. It is important not to assume bare areas are slow-to- emerge plants. When scouting fields check for low density stands of plants or bare patches. If you find you have thinning or a patchy field, check the areas surrounding the damage for larvae or set cutworm traps at night to determine if your field has been infested.
Because John caught the problem early and applied the appropriate insecticide, his field recovered. To avoid a serious problem in future, John will be on the lookout for irregular patches or thinning of plants frequently between May and July when cutworm larvae hatch and feed.