Our changing canola practices have been beneficial for flea beetles. Here are some tips to help you stop them from taking a bite out of your profits
Flea beetles are one of the most common and persistent insect pests in canola in Western Canada. They are present in virtually all areas and can cause significant plant losses when present at the seedling stage of the crop.
In the years since lindane was phased out (lindane’s federal registration expired in 2004), much has changed in our canola farming practices. Many of the changes increase the potential for flea beetles to cause problems.
First, there are simply more acres of canola. We have gone from a Western Canadian canola acreage of about 12 million acres in 2000 to over 18 million acres in 2011 — an increase of over 50 per cent. Obviously, there is a lot more habitat available for the flea beetles.
Canola rotations have been shortened in most areas. Ten to 15 years ago, it was much more common for farmers to use one in three year or longer canola rotations. However, in many areas one in two year rotations are now the norm, and it’s common to hear of farmers using a canola-snow-canola rotation. There are more opportunities for flea beetles to build up.
Secondly, we have gone to direct seeding and earlier seeding. Soil temperatures are generally much cooler than when there was more tillage conducted and seeding was later. These cooler temperatures generally slow the emergence and early growth of the canola seedlings and make them more susceptible to insect feeding.
A third agronomic change that benefits flea beetles is the lower seeding rates used for herbicide tolerant varieties. We no longer need to rely on crop plant competition to compete against weeds as we did with conventional varieties in the past. As well, we have moved largely towards hybrid varieties with the lure of higher yields. With these hybrid varieties comes a higher seed price, so there is a tendency for famers to reduce seeding rates as much as possible. These hybrid varieties generally are much larger seeded than past open pollinated varieties, so that for a given fixed seeding rate in terms of pounds per acre, there are far fewer seeds. This also dovetails with more recent seeding equipment advances, like independent row openers, that allow for more consistent seeding depth which further allows farmers to consider reducing seeding rates.
While these practices are good in terms of optimizing seedling emergence and reducing seeding rates, they still leave one fact. We generally have fewer numbers of canola plants per unit area then what we used to have. And that leaves far fewer plants for the flea beetles to feed on.
Compounded by all these conditions, we also have the fact that with the seed treatment insecticides, the flea beetle has to eat some of the plant and ingest some insecticide before it dies. Even if the insecticide is effective, with higher flea beetle numbers, fewer plants for the beetles to feed on and slower growing plants due to earlier and resulting cooler conditions, is it any surprise that we have more problems with flea beetles?
Another phenomenon has been noticed by entomologists and agronomists over the years. We have seen a bit of a species shift from the previously predominant crucifer flea beetle, which prefers warmer areas in the southern Prairies, to the striped flea beetle, which was previously found mostly in the northern Parkland areas and the Peace region.
The striped flea beetle can tolerate cooler temperatures than the crucifer flea beetle, so it has adapted to the conditions of early seeding into direct seeded fields better than the crucifer flea beetle.
Optimize your efforts
There are several ways to optimize flea beetle control efforts.
Treat your canola seed with a higher rate of seed treatment insecticide whenever available. For example, some varieties are available with the choice of either Helix or Helix Xtra. If you have the choice, choose Helix Xtra if you have had or are anticipating problems with flea beetles. As well, make sure it has a good fungicide package suited to the predominant seedling diseases in your area. This will help your crop ward off seedling diseases as much as possible.
Do whatever you can to get the crop to come out of the ground as soon as possible after planting and get off to a vigorous start. This means shallow planting (generally one half to one inch) in a firm, moist seedbed with an average soil temperature of at least 5 C. When the soil is warmer, seeds will generally emerge faster.
Use some seed-placed phosphorus for the “pop-up” effect. As well, have the nutrient content of your soil and seed tested. If other nutrients are low, consider using a seed nutrient dressing to enhance the nutrition available to the seedling.
Use a pre-seed burn-off to ensure that you don’t have moisture robbing weeds stealing available moisture away from your seedlings and slowing their development.
Make sure that you put as little fertilizer as possible (other than moderate rates of phosphorus) with the seed as higher rates of fertilizer can slow germination rates — the fertilizer can tie up available moisture. Higher rates of these fertilizers should be put away from the seed in a sideband, midrow or broadcast application.
Scout your fields regularly, starting a week after seeding, at least every couple of days until the crop is well established.
Be prepared to use a recommended insecticide for post emergent control, but only use it if the flea beetle feeding warrants it (25 per cent or more of the leaf area affected).
However, the proper use of available seeding practices to assist in as rapid and vigorous germination and early season growth as possible, combined with the judicious use of post-emergent insecticide applications wherever warranted, can help in reducing the chances that flea beetles will end up taking a big bite out of your canola profits at the end of the season. †