By Brian Hrudka
Flea beetle damage to an emerged canola crop is a relatively common occurrence across the Northern Plains every year. However, the timing and severity of damage can vary tremendously from year to year and even from one field to the next for various reasons.
In the spring, when the ground surface temperature warms to about 60 °F, adult flea beetles emerge from overwintering habitats, including canola trash, volunteer cruciferous plants and certain weeds that may be growing in non-crop areas. Flea beetles are dark-colored, oval-shaped, and less than 1/10th of an inch long.
The beetles feed on canola seedlings and quickly disperse across a field by jumping (like a flea, hence the name “flea beetle”) and flying. Infestations typically begin on field edges and move inward. Damaged plants have a “shot-holed” appearance. After mating, the female will lay her eggs in moist soil adjacent to the host plant’s roots and the adults die off.
From the cotyledon to four-leaf stage, canola plants are most susceptible to flea beetle damage, which varies according to pest density, stage of the emerged crop and growing conditions at the time of infestation. A vigorously growing canola plant can recover loss of up to 50 percent of its leaf area without significant yield reduction.
However, under conditions such as those found in many canola growing areas this past spring –slow emergence and plant growth due to dry conditions combined with warm temperatures that stimulate flea beetle activity – a flea beetle infestation can quickly damage a young crop to the point where the slow-growing seedlings cannot recover and the crop must be replanted.
Usually, a seed treatment insecticide will protect the seedling until it has grown past the susceptible stage. (Some feeding will still occur, as ingestion of the systemic insecticide is required for control.) However, when seedling emergence is delayed, the seed treatment insecticide may have degraded in the soil to a level that no longer provides flea beetle control.
Should such a break in seed treatment control occur, flea beetles can be controlled with an insecticide applied by ground or air. Key to a successful crop rescue is early pest identification through vigilant scouting and immediate spraying before the infestation damages the seedlings beyond the point that they can no longer recover.
Flea beetle damage may vary in adjacent fields which faced the same flea beetle pressure. This is the result of different emergence time and growth rates, planting times and depths, and seed varieties. One canola variety may be more susceptible than another only because it was at a more susceptible growth stage when the flea beetles appeared.
The most effective way to lower the risk of flea beetle damage is to delay planting. For many compelling reasons, producers tend to plant canola as soon as possible after the April 15 crop insurance planting date. Soils may be cold at that early time in the planting window and dry before spring rains arrive.
However, seeding into a warm, moist seedbed will promote rapid plant growth, allowing the crop to quickly outgrow the susceptible stage and any flea beetle damage. Also, with rapid emergence, a seed treatment insecticide is still present at a level that provides control.
In addition, calibrating equipment to optimal seeding depth, seeding at lower speeds, and ensuring proper fertilizer placement can reduce the risk flea beetle damage by encouraging good crop establishment and rapid growth. All of these practices will strengthen a crop and help it overcome any damage caused by flea beetles.
Brian Hrudka is the InVigor® Canola Seed Lead at BASF Corporation in Research Triangle Park, N.C.