Every new production season arrives with its own set of profit-munching insect challenges. Grasshoppers, wheat midge and sawfly can wreak havoc in cereal crops while flea beetles and bertha armyworm take their toll on the canola. The list keeps growing, and the ability of these pests to adapt to changing conditions is nothing short of amazing.
Of the three Prairie provinces, Alberta recorded much higher overall insect populations in 2014. Wet conditions make monitoring very difficult. This may have had an impact on the lower than normal counts in areas of excess moisture, like Saskatchewan, but there’s no doubt that some of the dry-weather bugs took a hit last year. In Manitoba, levels of crop feeding insects were generally at low to moderate levels, with the exception of some species of cutworms, flea beetles and grasshoppers, where populations were high in many areas.
“The good news about too much moisture is that insects like grasshoppers don’t thrive,” says John Gavloski, entomologist with Manitoba Agriculture, Food and Rural Development. “In some years that have prolonged wet and humid weather a lot of grasshoppers may die from a pathogenic strain of fungus. Grasshoppers climb high onto the plants after they’ve become infected, and will die clinging to vegetation high in the plant canopy. The body fills with spores and eventually splits, enabling the spores to spread easier from these higher levels.”
Some sun-loving nuisances may be feeling discouraged but wetter conditions have been much more welcoming for the humidity-hungry wheat midge and moisture-loving flies and maggots.
It’s all a question of opportunity, and weather conditions create all kinds of them, according to Scott Hartley, entomologist with the Saskatchewan Ministry of Agriculture. Hartley, like Gavloski, anticipates a good year for wheat midge, among other unwelcome guests.
“Wheat midge has been making gains in recent years, probably because of the wide-spread moisture,” says Hartley. “Southeastern Saskatchewan can expect very high numbers of wheat midge this year, extending north to Regina. The East-central region, including Yorkton, should also see them in high numbers. Moisture is tough on grasshoppers but very favourable for midge and root maggots.”
Bob Elliott, research scientist with Agriculture and AgriFood Canada in Saskatoon, specializes in pests that pose the biggest threat to canola, including flea beetles and leaf hoppers. Wide-spread canola acres have made flea beetles a well-known problem for producers and they’re often managed very effectively with seed treatments. In recent years, Elliott has seen a dramatic shift in both distribution and abundance of flea beetles that could also have been influenced by weather conditions. This shift may change the strategy for producers.
“Crucifer flea beetle has traditionally been more prevalent in the south because it likes warmer, drier conditions, while the striped beetle was exclusive to more Northern locales,” says Elliott. “But over the past two years there’s been a very substantial shift. Striped beetles are now on the move across a much wider area. The speed of this transition has been shocking.”
From a dominant position in 2004 to 2010, crucifers declined significantly in a period from 2011 through 2014 while the striped beetles made huge strides.
“More effective treatment of crucifer has allowed other species to move in and take its place, but weather also plays a big role,” says Elliott. “The crucifer needs a warm and dry climate and the striped prefers the cooler, wetter conditions that we’ve seen more of over the past few years. As one population recedes, another species is ready to take over.”
Plan of attack
Careful scouting in 2015 will help you make the best decision for 2016 treatments, according to Elliott. He advises diligent monitoring in July and August, when summer populations emerge. The two species will hatch about two weeks apart, the striped beetle appearing in late July and early August, followed by the crucifer in later August. This staggered arrival can make scouting more difficult, and also more important.
The agronomic benefits of early seeding are well known. A general shift to earlier planting dates has created some interesting pros and cons for things like flea beetle populations. Flea beetles will move in at about 14 C, the adults beginning to feed on young plants and females laying eggs on the stems, near the ground. Larvae will hatch and burrow into the roots, creating entry for disease and pathogens. Ideally, earlier-seeded crops will have the chance to develop ahead of the highest-risk stage for insect attack. But when cool, wet weather creates a stalled growth stage, seed treatment can wear off and turn the opportunity in favour of the beetles’ advance.
“Seeding date won’t affect the emergence of beetles, but could have a great impact on the potential for damage,” says Elliott. “Early seeding can help to ensure that canola flowering is over by the full heat of summer and it can also help to avoid voracious eating during the plant’s more vulnerable stage. Early seeding can reduce damage by summer beetle populations by 40 to 60 per cent, under good conditions.”
When it comes to beetles the key is in telling one from the other, because there’s a huge difference in the efficacy of seed treatment between the two species. Neonicotinoid seed treatments provide excellent control of crucifer flea beetles under warm, dry conditions, while the diamide group of insecticides also provide a higher level of control on striped flea beetles and under cool, moist conditions. Another option for seed treatment is a mix of both neonicotinoid and diamide, for those fields in which you find both populations this year. Cost and insecticide load are both key considerations, but a mix could be the best option for 2016, if striped flea beetles are the dominant flea beetle species or cutworms are also a concern.
The right treatment and spray strategies can’t control the weather, but they will provide the best line of defence against the most prevalent Prairie pest threats, both for this season and the next.