It’s going to happen – your healthy canola crop is bound to attract some less-than-savory critters, such as bertha armyworms, lygus bugs and diamondback moth larvae. Canola will suffer pest outbreaks - but with a little work on the front end, you can limit the economic cost of insects on the crop. Scouting your fields regularly helps you to identify and manage those hungry bugs.
Here are a few tips when scouting your canola:
1. Find the right scouting method for each insect. Some thresholds are based on sweep net counts, while others are monitored by larvae found after shaking plants.
2. Choose the best time of day to scout. Some bugs are early risers and some are more active in the middle of the day. Also consider that insects may be lower down in the canopy on hot afternoons or in heavy winds.
3. Be proactive. Don’t just wait until you see insect damage. Know when to expect bugs and be ready to head them off. And then keep checking.
4. Take action if economic threshold numbers are met. For example:
- Bertha armyworm – Research shows that per square metre, each bertha armyworm larvae can cause a 0.058 bushel per acre loss. Once numbers reach the economic threshold, which varies with the price of insecticide and the price of canola, spray as soon as they start feeding on pods.
- Lygus - One lygus can cause a 0.1235 bushel per acre loss at the late flowering to early pod stages and 0.0882 bushel per acre loss at the late pod stage. While thresholds vary based on prices, researchers advise against insecticide applications when lygus numbers are below 50/10 sweeps.
- Cutworms: Thresholds for cutworms in canola sit around 25-30 percent. Below 25%, canola plants may be able to compensate for some of the damaged or destroyed plants. If bare spots develop, spray around these patches to limit their size.
- Diamondback moth larvae: Thresholds are 100-150 larvae per square metre in immature to flowering plants, or 200 to 300 larvae per square metre in plants with flowers and pods.
- Cabbage seedpod weevil: The economic threshold is 25 to 40 weevils in 10 sweeps. The higher the price of canola, the lower the threshold.
- Flea beetle: The point at which foliar insecticide is recommended is 25 percent – canola can handle up to 50 percent defoliation, but aggressive flea beetles can move from 25 percent to 50 percent in as little as a day.
5. When spraying is necessary, choose a product with a pre-harvest interval that’s right for you. For example, Coragen™ has a 1-day interval from spray to swath, whereas Lorsban™ 4E has a 21-day interval, and RIPCORD® has a 30-interval. Whatever product you use, always read and follow label instructions.