Most Unwanted List: Pests

Friday, September 23, 2022

The Top 5 undesirable insects that are coming for your crops this year.

by Becky Dumais

Every year producers deal with pests creeping onto the farm – those unwanted guests that infiltrate the field, eat their way through crops and hamper yields and productivity.

Five invertebrate pests we are expecting to invade Prairie fields this season are: grasshoppers, flea beetles, lygus bugs, cutworm, and wheat stem sawfly.

With this list of potential suspects in mind, how can producers prepare for these crop-crippling creatures?

To stay on top of what's going on in your fields you have to scout. "Every time you go out in the field you should carry a shovel with you," says George Lubberts, an agronomist in Alberta, "so you can dig up plants if you see something happening. Also keep a notebook in your vehicle to write it down and then in the winter you can transfer (your notes) over to your permanent records."

He also advises farmers to monitor each field to know what the pest is – and if there's an issue. "Don't spray just because your neighbour is spraying – we've seen that happen. If you're not sure you can call your local CCA or agronomist to find out what's actually happening in the fields," he adds.

Grasshoppers

Grasshoppers – often clearwing, migratory, and two-striped – were an issue last year, occurring in a widespread region across the Prairies, according to John Gavloski, an entomologist at Manitoba Agriculture.

"We've had some dry weather for a few years in a row which makes it easy for grasshoppers to build their population. We've been seeing the grasshopper populations increase over the last few years."

In Alberta, Shelley Barkley, insect technologist at Alberta Agriculture and Rural Development, says the population has been quietly growing over the last few years because they thrive so well in hot, dry weather. "In 2021 we had a beautiful fall. It was fantastic and the females had a long time to lay a lot of eggs. So, there is a big potential (of them) in the ground right now just waiting for time to hatch," she adds.

Lubberts commented there was "a huge problem within southern Alberta to the point where some farmers, combined with the drought, lost their crop. Last year we started seeing them in late June and July."

In Saskatchewan, James Tansey, provincial specialist in Insect/Pest Management at the Ministry of Agriculture, agrees that there was definitely an increase from the previous year, but is taking a measured approach to these events.

"I don't think we're in a state of alarm at this point yet," he says. "What we had were relatively localized outbreaks. The southwest was characterized by large populations; we also had some in the northeast. Most regions of the province had heavy populations. There was a lot of spray put down and a bit of a shortage on some of the control products because of supply chain issues – a bit of a double- whammy for some growers. We anticipate that the supply chain issues will be addressed."

When it comes to management, Gavloski says start scouting field edges early. "It's easier to control them if they're numerous in late June and early July when they're concentrated around that field edge. Often what does happen, though, is people don't notice the problem until (the pest) has moved into the crop."

Adults that have moved into the crop are trickier to control, "and usually when they're more damaging (to crops) is when they're adults. If you're trying to control them in late July and early August it'll be a trickier battle. The insecticides don't work as well." This would also mean entire fields would have to be sprayed, not simply the field edge.

"All producers can do is be out and scout – they know their farm, they know where there was a problem on their farm," says Barkley. "They're easier to deal with when they're little. Once they get wings they can move all over. You need to pay attention to economic thresholds. Nothing replaces boots in the field."

Flea beetles

Beware the flea beetle – both striped and crucifer.

"They're an issue for canola producers every year," says Meghan Vankosky, a research scientist at Agriculture and Agri-Food Canada in Saskatchewan, and co-chair of the Prairie Pest Monitoring Network.

They'll be most troublesome in canola from emergence to the two to three-leaf stage.

"Wherever you grow canola you're going to see flea beetles. Once your canola's passed that stage you probably don't have to worry about them anymore," says Lubberts. "If it's drier (weather-wise) it might be harder for the canola to get through that."

With canola being such an important Prairie commodity, all farmers should be watching their fields. "They were affecting canola crops throughout the Prairies," says Gavloski, including the Peace River area of Alberta. "They've been super abundant in recent years.

"There's just so much canola being grown – I don't think we're ever going to starve out a flea beetle. They've got lots of food."

He's hopeful things will be different this year "if we have good moisture conditions where the canola is germinating and growing through the seedling stage quickly – that can reduce flea beetle damage significantly."

Alberta had large populations going into last winter, according to Barkley. "I was in fields at the end of July and they were up on the pods, eating (them)." She adds that, with a big population overwintering under trees, in leaf litter and field margins, "it could be a year where they're bad. Again, you need to be out scouting. You need to be watching that baby canola and be out there scouting almost daily to know what's going on. The other thing to know is understanding what 25 per cent feeding damage looks like on those leaves."

Last year was prime for flea beetles in all regions of Saskatchewan and western Canada, right into the Peace River Country. "We continue to see northern areas dominated by striped flea beetle," says Tansey. "There were mixed populations through the south and some of these were dominated by striped flea beetles as well. The Regina area continues to be dominated by crucifer flea beetle."

Striped flea beetles are less sensitive to insecticides from multiple groups, most notably the neonics, Tansey says. "What does seem to be encouraging is that the BUTEO start efficacy for striped flea beetles seems to be quite good. It is a premium product and it does seem to (work). However, this product still requires that flea beetles feed to be exposed to the toxin, so large numbers can still cause damage."

Insecticide treatments on canola seed are beneficial, according to Gavloski. "That will give people roughly three weeks, maybe four, of protection from the day you seed – if you have favourable growing conditions." After that, he says farmers will have to keep an eye on the crop and monitor it.

Wheat stem sawfly

The heart of sawfly country is around the area of Foremost, Alta., in the county of Forty Mile. "I was in fields (last year) that had stem cuttings of up to 65 per cent and more," reveals Barkley. "It's quite devastating because ... the crop goes down before the combines can get in the field."

This is another insect that responds well to hot, dry conditions, which Vankosky says were Prairie-wide. Vankosky attributes the sawfly's reign to its parasitoid only having one generation, instead of two, when the crop matures too early, and exerting less control as a result. Wheat stem sawfly escapes that management when the weather condition is in their favour, she says. "Generally, people have been saying if you had low levels of wheat stem sawfly in 2021, you're likely to have higher levels by the end of 2022."

One form of management is through stem height, because the parasitoid overwinters higher up in the wheat stem than the sawfly's larvae do. "Taller stubble is a very good conservation method to help promote those parasitoid populations."

Lygus bug

Vankosky says lygus bugs could be an issue again if we experience another hot and dry year. "They really seem to respond well to those conditions. Last year their numbers were quite high and with stressed crops, the lygus were a concern, especially when they started attacking the flowers on the canola and feeding on the pods a bit later in the season too."

They're found across the Prairies, though there were different species occurring in Alberta canola than in Manitoba. "Levels were high last year – higher in some provinces than others," says Gavloski. He says some pockets in Saskatchewan and a few areas in Manitoba reached economic thresholds. "We did have some in several crops, not just canola: dry bean crops got some feeding damage. In Saskatchewan they were in big numbers and there was some spraying in flax. It's tricky when they're numerous in flax because we really don't know what a good threshold is in flax (yet). Research on lygus bugs in flax found that under good growing conditions populations of up to 100 per 10 sweeps were not economical."

While a problem at high levels, lygus bugs can be beneficial at very low levels. "There's been data to show they're actually stimulating production of more pods," Gavloski says. "They'll damage a few of the buds and flowers but then the plant overcompensates and produces more."

Economic thresholds for lygus bug management in canola have been updated because of new research on modern varieties, says Gavloski.

Cutworm

Last year Alberta boasted ideal conditions to allow cutworms to lay eggs, plus Barkley says regrowth in the fields gave moths plenty of places to lay them where the larvae would have best success. "Fields with regrowth would be really attractive to them," she notes.

In the rest of the Prairies, Gavloski says they were also an issue. Although not every field was affected, "they were localized and sporadic. You'd have an area that had big problems and another where producers said they weren't a big issue."

Manitoba's dominant species has been redback cutworm, and also dingy. "They often go in cycles which are regulated by natural enemies and/or weather," notes Gavloski. "Sometimes the cycles are like a bell curve where they build up for a few years and you get a peak of a couple of bad years, then things start to decline. Last year we did have some significant cutworm issues, but less than we did in 2020. Cutworms can still be a problem – it's rare to go from a bad year to nothing."

In the drier areas of the Prairies, pale western cutworm can be a challenge because it feeds mostly below ground. "Pale western feeds below ground and can cut plants below ground. They're hard to kill because they're below the soil and you can't get an insecticide to them as easy as you would some of the other species. They're often more of a concern in southwestern Saskatchewan and eastern Alberta."

As with all other pest species: scout. "Treat if levels are high enough," says Gavloski. Because cutworms hide in soil by day and come out at night to feed, your first clue that they're active is seeing clipped plants. "If you notice that, then you have to dig around the plants and get an idea what the population's like. If you've got a lot of young cutworms and you're seeing lots of damage, then you can apply a foliar spray that will help. We could still have another year or two with localized problems."

Barkley agrees. "Get out in the field and dig around the outside edge of (a bare spot) and see if you can find them and determine which kind of cutworm they are because that will determine your control method."

To help farmers and agronomists, Vankosky says the Prairie Pest Monitoring Network has some different predictive models for insect pests. "That's one place to go to get some information about when certain life stages of insects might be active in their fields. That can help them to time their scouting. It's not infallible but it is some information that can help time scouting and decision-making. Predictions can be difficult, Vankosky says.

"If the trend continues in terms of being drier than normal, and warmer than normal, then we really do see certain species responding quite well. Those include grasshoppers, wheat stem sawfly, crucifer flea beetles – but then if we have a rather cooler and wetter spring – which would be nice – grasshoppers would respond quite poorly but then the wheat midge could be a bigger problem, and striped flea beetles tend to do better in cooler and wetter conditions.

"The spring weather that we'll end up having is going to be quite pivotal in determining which of these insects are probably going to be a bigger problem." BF