WESTERN PRODUCER — Farmers who think this year’s delayed spring melt might lead to lower flea beetle pressure across the West should think again.
There’s no way to predict what the spring flea beetle risk will be, said Keith Gabert, agronomy specialist at the Canola Council of Canada.
An accurate assessment won’t be possible until the spring melt is complete and canola crops begin to emerge.
“There’s absolutely no way to tell,” said Gabert, when asked to predict this year’s risk.
“Even our (observation of) fall populations has rarely told us what the spring (risk) will be like.
“We’re relatively apprehensive that southwestern Manitoba, which has had pretty significant flea beetle pressure for the past three years running, is in line… for a fourth year (of heavy pressure),” he added.
“But even that isn’t a sure thing. The line that I use on people is that 20 percent of the Prairies are going to have a significant flea beetle issue in any given year, and I have no idea where that 20 percent is going to be.”
According to the Canola Council of Canada, flea beetles are the greatest insect pest risk affecting canola productivity in Western Canada.
That’s why the council encourages growers to think ahead about managing flea beetle risk this spring. To minimize losses, growers should be prepared to take quick action.
In a recent interview with The Western Producer, Gabert said growers who want to minimize flea beetle damage should focus on two main objectives.
The first is achieving rapid canola emergence and establishing healthy plant populations.
The second is maximizing the impact of foliar sprays. That means using insecticides properly, according to label recommendations and applying them at the correct time.
According to Gabert, one of the most effective ways to reduce flea beetle damage is to ensure that the crop emerges quickly. Growers should calculate seeding rates carefully, aiming for optimal plant densities of five to eight seedlings per sq. foot.
Seeding rates should always account for reasonable levels of seedling mortality.
In the past, the canola council has urged growers to seed canola crops early to avoid the risk of heat blast during the crop’s critical flowering period.
But with the proliferation of striped flea beetles across Western Canada, that message is weakening, Gabert said.
Striped flea beetles typically emerge from wintering about a week earlier than black or crucifer-type flea beetles. Because of that, early -seeded canola crops that are sown into cooler soils and slow to emerge are often more prone to flea beetle damage.
An early-seeding strategy might have been more effective when crucifer flea beetles were the dominant species, Gabert suggested.
But today, striped beetles represent a more significant risk than crucifers in almost all parts of Western Canada.
“The flea beetles that growers are concerned about in the spring, for the most part, have been striped flea beetles for years now,” Gabert said.
“Southern Manitoba still has a blend of both and the Lethbridge area probably has a blend of both. But for the most part, I would say striped flea beetles are the dominant concern across the Prairies.”
Gabert said management strategies are no different for the two species.
“Generally, early-seeded crops tend to be seeded into cooler conditions and often into slightly poorer seed beds,” he said.
If possible, growers should seed cereals before canola because cereals can typically tolerate cooler soil temperatures better than canola.
Other steps that can be taken to ensure rapid emergence and optimal plant densities include regulating seed-placed fertilizers and using recommended seeding rates.
The canola council recommends using only phosphorus in the seed row and applying at rates of 20 pounds per acre of actual phosphate.
Higher rates of seed-placed fertilizer can add more stress during germination and emergence, slowing the pace of growth and reducing stand densities.
In high-risk areas, growers should also use an advanced seed treatment, such as Buteo Start, Lumiderm, Fortenza or Fortenza Advanced.
Because uncontrollable factors such as air temperature and dry soil conditions can impede rapid emergence and vigorous crop establishment, a growers’ second line of defence against flea beetles is the use of a foliar insecticide.
To ensure maximum effect, they must be applied properly and at the correct time, Gabert said.
Economic thresholds for when control measures are necessary are when flea beetle damage exceeds 25 percent cotyledon or leaf area loss.
In warm weather where flea beetle populations are high and feeding is occurring on a slow-growing crop, the window for spraying can pass quickly.
Scouting should occur frequently and growers should anticipate the speed at which damage might occur.
Spraying equipment should be ready for action at a moment’s notice.
Proactive spraying can begin before 25 percent defoliation.
In some cases, early spraying around the headlands of the field may provide effective control when feeding damage is localized and insect migration is limited. Applying foliar insecticides on field headlands can be particularly effective if windy conditions prevent beetles from flying and spreading quickly throughout the field.
Gabert warned flea beetles can spread rapidly throughout an entire crop if the right conditions exist. Frequent scouting in all areas of the field is always recommended.
The best time to apply foliar sprays is when flea beetles are actively feeding, typically in warm, dry and calm conditions.
Spraying in cooler weather and overcast or wet condition may not produce intended results because flea beetles often take shelter in the soil when conditions are not conducive to feeding.
Unlike seed treatments that take effect when flea beetles begin feeding on canola seedlings, foliar insecticides rely on direct contact with the flea beetle target.
For this reason, it’s important to achieve full coverage when spraying.
Because flea beetles are a small target, effective contact requires adequate amounts of water and nozzles that produce a finer mist.
Gabert recommended rates of at least 10 gallons per acre for effective coverage.
Growers should also check labels for specific nozzle recommendations.
Low-drift nozzles, which are a good practice for some herbicides, produce a coarse spray droplet that may not provide effective contact with the ground or insects.
Temperature can also have a significant effect on insecticide efficacy.
When temperatures are higher than 25 C, malathion and Sevin XLR may provide better results.
In temperatures below 20 C, pyrethroid products such as Decis, Pounce, Perm-UP, among others, will show better results.
Canola crops are vulnerable to flea-beetle related yield losses from the time they emerge until they reach the four-leaf stage.
Feeding that occurs after the four-leaf stage is usually inconsequential to overall yield potential.
According to Gabert, the most important objective among growers should be rapid emergence, rapid establishment and healthy plant densities.
Together, those conditions will narrow the active feeding window and minimize potential losses, especially when used in combination with foliar sprays.
“If the spring favours a nice, rapid, uniform crop emergence, we usually don’t need to have a flea beetle conversation with growers,” Gabert said.
“But if spring conditions make those crops struggle, particularly if it warms up quickly and brings those flea beetles hungry out of their winter habitat into a slow growing crop, then all bets are off.”
For more information on flea beetle management and how to make spray decisions, growers should review the Canola Watch fundamentals articles located online at www.canolacouncil.org.
Contact brian.cross@producer.com
