At a forage workshop hosted by the Canadian Forage and Grassland Association at the University of Manitoba in March, Manitoba Agriculture entomologist John Gavloski highlighted several key insect pests that can affect forage production and shared strategies for managing them.

Grasshoppers

Grasshoppers are a common pest in Prairie fields. Canada is home to 129 species of grasshoppers, but very few of those cause crop damage. There are only four or five grasshopper species that are considered to be pests, and of those, three are responsible for most of the damage.

“The top three grasshoppers in our survey this year are two-striped, which has been our dominant species in recent years, followed by either clear-winged or migratory,” Gavloski says.

All three have a similar life cycle. They all overwinter as eggs, laid in clusters of 20 to 30. The individual eggs resemble grains of brown rice.

“If you can dig those up easily, then you know you’ve got a decent grasshopper egg population,” Gavloski warns.

—> MORE ON FORAGES: Managing diseases in alfalfa

The ideal time for control is when the grasshoppers’ wing buds become visible. At this stage, the hatch is likely complete.

“Try to figure out what those newly hatched populations are like,” he says. “That will help you with your decision-making later on.”

Farmers can also lean on provincial grasshopper risk maps. Each of the Prairie provinces puts out a risk map in the fall based on samples taken, usually in August. The maps can help estimate the next season’s egg-laying potential.

While these maps can help, Gavloski warns they’re estimates and don’t guarantee outcomes for the following season. Weather conditions after the surveys have been done can affect populations. A warm fall with a late frost can mean there is more development within the egg, and the hatch could come sooner. And while the eggs are waterproof, heavy rains after the hatch, when the young grasshoppers are small, lack fat reserves and need to feed, can lower survival rates.

“They’re more vulnerable when they’re really tiny,” Gavloski says. “They get disease, they get bloated and they can drown.”

—> MORE ON GRASSHOPPERS: Reduced-area pest spraying can still hit moving targets

Economic thresholds: Estimating whether grasshopper numbers have reached the economic threshold can be challenging.

Gavloski estimates grasshopper populations by walking 50 metres along a field edge or ditch, selecting five random one-metre square areas and counting the grasshoppers that jump as he approaches. He then disturbs the plants to check for remaining insects.

These counts provide an estimate of the grasshopper population. The process doesn’t give very accurate results, but can probably let you know if you’re near the threshold.

“Usually, you can get a ballpark range,” Gavloski says. “If you think it was somewhere around 12 to 15, that is good. You don’t have to know that it was actually 13.”

For forage crops, the economic threshold for grasshopper control is generally considered to be eight to 12 grasshoppers per square metre.

Control methods: Gavloski recommends using what is called the Reduced Area and Agent Treatments (RAATS), which involve treating alternating swaths of land. This method works because grasshoppers move from untreated areas to treated areas. Research done in Wisconsin has shown RAATS can provide very good control while using half the insecticide.

—> MORE ON FORAGES: Grow forages, starve weeds

“The results of the research showed they were getting 94 per cent control when they sprayed the whole rangeland, but they were able to get 81 per cent control by only doing half of the rangeland,” Gavloski says.

Insecticides such as Coragen (chlorantraniliprole) are commonly used to control grasshoppers. Coragen is effective, with relatively low toxicity to pollinators. Generic insecticide versions have made treatments more affordable.

Cutworms

Cutworms are a diverse group of pests in Canada. Gavloski spoke about three different categories of cutworms: climbing, surface-feeding and subterranean.

Climbing cutworms climb plants at night to feed, then retreat underground or under debris during the day. Unlike other cutworms, they don’t cut plants but leave feeding damage on leaves, which can be misleading when scouting. The dingy cutworm is the most common climber in Manitoba. It can be identified by small leaf-like markings on its body. To find them, dig around damaged plants.

Surface-feeding cutworms crawl along the ground and cut plant stems, leaving severed plants behind. If you see cut plants, dig around to find the caterpillars nearby. The redbacked cutworm is a common surface-feeding species. It is recognizable by two red lines running down its back.

Subterranean cutworms live and feed underground, making them difficult to detect and control. The glassy cutworm is an example of a subterranean feeder. It prefers grasses over broadleaf crops and is commonly found in forage and cereal crops.

Gavloski also pointed out that some infestations can appear in patches. The patchiness can depend on egg-laying patterns the previous season, but it can also depend on topography. In more rolling landscapes, the warmer, southern side of the slopes tends to attract the bugs.

Economic thresholds: Gavloski didn’t speak to economic thresholds in his presentation. Manitoba Agriculture’s website says economic thresholds haven’t been well researched for cutworms, but included some anecdotal thresholds for various crops.

For alfalfa (the only forage crop listed), the website suggests four to five larvae per square foot (30 cm) as a threshold. Otherwise, farmers can just make a judgement based on the level of plant injury. Visible, widespread damage that threatens plant stands would obviously signal the need for control.

Control methods: Management strategies depend on the species. Coragen Max is the only insecticide registered for cutworms in forages — and while Gavloski says more options are needed, the pesticide is effective.

“It is a very good product for cutworms, at least the ones that surface feed; it’s got residual, and it is basically harmless to bees and many beneficial insects.”

Since cutworms are most active at night, insecticides should be applied late in the afternoon or evening.

Unfortunately, the effectiveness of insecticides to control subterranean species is “hit-and-miss,” Gavloski says. “Because they’re not coming above the ground to feed, they can be a real nuisance to manage with insecticides.”

Targeted spraying of affected areas can be used in situations where an infestation is not widespread.

“If the problem is small — say, 10 or 20 acres have a lot and the rest of the fields aren’t bad — you can patch-spray for cutworms.”

Cereal armyworm

The pest Gavloski refers to here shouldn’t be confused with the better-known bertha armyworm, which is mostly a concern for canola growers. As the name suggests, cereal armyworms are more likely to be found in forage grasses than alfalfa stands. It is also known as true armyworm or simply as “armyworm.”

Adults don’t overwinter in Canada but migrate from southern areas, often carried by wind currents in spring and summer, and while they have a particular affinity for timothy, most forage grasses are excellent hosts for armyworms.

“When the adults arrive, they’re looking for a lush, dense grassy stand to lay their eggs into,” Gavloski says. “So a perennial grass is just ideal … that’s where the eggs often end up.”

However, if they defoliate enough in an area, they will start moving into other areas (these movements are why they’re called armyworms), and, while their preference is to feed on grasses, they may feed on broadleaf plants in lieu of a grass crop if that’s what’s available.

Armyworm larvae have distinct stripes, with a V-shaped marking on their heads. The colours can vary, but those striped patterns are usually visible. The adult moths are light brown with white dots on their wings. Armyworm larvae feed primarily on grasses and are often found in forage stands, especially in early spring.

When scouting for armyworm larvae, check multiple areas of the field, as populations can vary within a single field. Shake plants and inspect the soil for larvae, paying close attention to plant debris, soil clumps and cracks.

“During the day, they’re trying to hide, so they’re underneath the debris and may go into the cracks in the soil,” Gavloski says. “So you have to look in the cracks, peel away the debris and do your counts.”

In cereal and grass crops, begin scouting in late June and examine at least five areas, focusing on patches of lodged plants and grassy weed infestations. Fields or sections with significant bird activity should also be monitored, as birds often feed on armyworms. Additionally, check the backs of larvae for parasite eggs, which can indicate natural control.

Economic thresholds: The threshold for control varies by crop. For forage grasses, it’s generally five larvae per square foot (929 cm²). However, as mentioned, they love timothy. Instead of feeding on the leaves before moving on to the heads like they do with other grasses, with timothy, they attack the heads first. As a result, they may require intervention even if the threshold isn’t met.

“Sometimes, it will pay to control them at levels below a threshold, depending on where they’re feeding and how much damage they’re doing,” Gavloski says.

Control methods: Insecticide applications should be timed for the evening or late afternoon, as armyworms primarily feed at night.

As with cutworms, chlorantraniliprole is the only active ingredient registered for armyworms. The products Coragen Max, Coragen (the pre-Max version) and a new generic version called Shenzi are available for farmers to use.

Alfalfa weevil

As the name suggests, the alfalfa weevil is a major economic pest for alfalfa crops, but will also feed on other legumes such as clover, making it a major concern for many farmers growing forages.

Adults overwinter under plant debris and soil in and around alfalfa fields and emerge in spring, feeding on alfalfa leaves. Round, elongated holes in the leaves are an indication of adult alfalfa weevils feeding.

When females are ready to lay eggs, they chew a hole in the stem and deposit from one to 40 eggs. When they hatch, the larvae will feed upon the stem before moving to fresh buds and leaves. After the larval stage, they make silky cocoons that, if the infestation is widespread, can be visible as a white haze over the field.

“People often first notice this driving by their field and see the crop is looking kind of frosted,” Gavloski says. “If you see this, you’ve probably got lots of feeding, and you probably should have been in there earlier.”

As a general guideline, he recommends scouting for the bugs in early June and continuing weekly checks.

“They should be hatching out by then,” Gavloski says. “You should be on top of things before it gets too bad.”

Economic thresholds: Alfalfa weevils cause significant damage, particularly to young alfalfa crops. The general action threshold for larvae varies based on crop height. For hay crops under 30 cm, the threshold is one larva per stem. For crops between 30 and 40 cm, it’s two larvae per stem. If three larvae per stem are found, control measures are generally needed.

Control methods: For hay crops, cutting the plants early is the main strategy used to control the insects because the larvae will starve or desiccate after cutting. Several insecticides are available for use, but many only provide partial suppression.

“Our insecticides don’t always work well for alfalfa weevil,” Gavloski says.

Natural predators, such as parasitoid wasps (bathyplectes and oomyzus), can help control alfalfa weevil populations. These predators can sometimes reduce the need for chemical control.

Lygus bugs

Gavloski also touched on lygus bugs. They are primarily a concern for alfalfa seed producers rather than forage growers. Lygus bugs are sap-feeding insects that use their beaks, like mosquitoes, to inject enzymes into plant tissues and suck up the sap. They target nitrogen-rich growth, damaging buds, seeds and flowers.

While there are suggested economic thresholds for control of the bugs in seed alfalfa, and insecticides are available, control is not recommended for alfalfa grown for hay.

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Haley Catton, a research scientist with Agriculture and Agri-Food Canada at Lethbridge, says producers need to focus on conserving beneficial insects while simultaneously managing pest insects.

“There are two basic rules: don’t hurt them, and try and help them,” Catton told the Farming Smarter conference and trade show in Lethbridge last month.

Many beneficial insects help to promote synergies and make the most possible use of other ecosystem service providers. Examples are predators and parasitoids, pollinators, microbes in the soil, decomposers and earthworms that improve soil structure and water filtration.

“There are a whole bunch of these things, and any management decision I make, it’s best to consider on a holistic lens, doing the same whether it’s tillage, irrigate or whatever. Considering them in context of all these different things will be the best decision,” Catton says.

“They call that eco-stacking — stacking this on top of that. Stack the beneficials on the soil microbes, think of it all. I don’t envy farmers, actually, because you have so many decisions to make, and some of them are on a short timeframe. Some of them are on a long timeframe, some of them affect your fields, some may have an effect on regional pest populations.”

Beneficials in the field are either predators or parasitoids. Predators include ladybird beetles, ground beetles, lacewings, syrphid flies, aphid midges and yellow jacket wasps that chase down the cutworms and eat grasshopper eggs.

Parasitoids, meanwhile, lay their eggs inside an insect host such as a cutworm, and the babies will eat the cutworm from the inside out.

“These things are massively important. Beneficials kill pests, they scare pests and change their behaviour,” Catton says. A cereal leaf beetle, for example, “will drop off the leaf if it is scared of a predator, and they eat and poop, which is part of nutrient cycling.”

For wheat stem sawfly, a pest on Prairie farms for more than 100 years, Bracon cephi is a parasitoid.

“It is killing a lot of your sawflies. The adult looks like a wasp and she lays her egg in a wheat stem and the larva feeds inside the wheat stem. That parasitoid will find stems with sawflies in them, sting them from the outside, paralyze the larva, and its babies will eat that larva alive,” Catton says. “It’s actively preventing cutting from your fields, but it’s small and it’s out there.”

Prairie field beneficials are also numerous, with plenty of diversity.

There are more than 200 species of ground beetles in Prairie fields. In recent biodiversity studies, 62 such species were found in Vauxhall plots over four years and more than 37 were found over two years at Lethbridge, while another study Catton is just wrapping up found 82 ground beetle species.

It can be difficult to put a dollar figure on the work done by these beneficial insects, Catton says.

“There are so many variables going on. When a problem is prevented — say, an aphid population is prevented from outbreaking because those ground beetles, those beneficials are eating them — a prevented problem is an invisible problem. There is a lot of work being done by these beneficials that we don’t even notice because it’s not being quantified.”

Catton encourages producers to avoid hurting beneficials by not using insecticides unnecessarily. This can be accomplished via scouting and following economic thresholds. Producers who do need to use insecticides can apply “soft” versions and make sure not to use them when beneficial insects are most vulnerable.

“My talk is not about pollinators, but one way of thinking of protecting pollinators is to not spray when they are out flying, not during those daylight hours,” Catton says.

Averting harm and helping beneficials can include offering an alternative habitat with shelter, nectar, alternative prey and pollen. Finding that balance between weeds/pests and beneficials is key.

“It is good to have some pests around. If you sanitize your fields with no pests, then the predators have nothing to eat. You want low levels of pests around.”

Pest management is a tool box, with many tools available to diversify control, be they cultural, physical, biological or chemical.

“It’s important to have different tools because if all you have is a hammer, then everything looks like a nail,” Catton says, referring to the beneficial and unwanted insects.

“Cultural controls are crop rotations, physical controls are trap crops, biological controls are beneficials, and it interacts heavily with the insecticides. When you spray a pest, most of the insecticides we use are lethal to those beneficials, too.”

The International Organization of Biological Controls has been compiling a list of “softer” insecticides. While not currently done in Canada, Catton says Australian researchers used that data to compile a pesticide toxicity table for beneficials, publishing a paper in 2024.

“They did find some main messages that some insecticides are consistently harder than broader-spectrum and some are soft,” Catton says.

For more informtion about beneficial insects, visit fieldheroes.ca.

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Lumivia CPL’s active ingredient is chlorantraniliprole, a Group 28 insecticide. Under its new label, which took effect in July, for grasshopper suppression in wheat, oats, barley or rye, the treatment can be applied at 40 mL of active ingredient per 100 kg of seed.

This “exclusive” label update is an important development because it “reduces the need for farmers to apply post-emergence treatments,” the company says. That said, if pest pressure is high enough for a follow-up foliar application, you’ll need to wait at least 60 days from seeding if you plan to use any Group 28 product.

The post Label boost for Lumivia appeared first on Grainews.

Forage and seed producers heard about the benefits of night spraying for red clover crops during the Saskatchewan Forage Seed Development Commission’s recent annual meeting. The SFSDC had conducted two on-farm experiments of night spraying in the province’s northeast in June 2021.

During the meeting, Graham Parsons, pollinator biosecurity specialist with the Saskatchewan agriculture department, identified the pollinators that benefit from nighttime pesticide application as farmers manage certain pests.

The lesser clover leaf weevil “is more active in the night, in the canopy and stuff, so the spray actually for that pest was more effective during the night time as well,” he told the meeting at White Fox, north of Nipawin.

“So it’s kind of a win-win both ways: better for the pollinators and better for spraying for the pest as well.”

READ MORE: When a crop pest isn’t a crop pest

Producers are seeking ways to control the lesser clover leaf weevil. Management practices range from spring burning to encouraging parasitoids, but chemical application of pesticides has been the most effective.

Northeastern growers are under more pressure from the weevil, which lays eggs from May and into June and July when the crop starts to flower, according to a University of Saskatchewan study.

The commission said day and night spraying was done in June 2021 before clover flowering. Traps were set to identify the beneficial pollinators present in the field 24 hours before and after the spraying applications.

“Success then would be measured as ‘no decrease’ in trap catches for the 24 hours post-spray in relation to pre-spray samples, night spray compared to UTC (unsprayed treatment control)… there is no indication that night spraying was more deleterious to commercial or natural pollinators than day spraying,” the report said.

Parsons identified an abundance of bees in the traps. Bees of any kind are the gold standard of pollinators, he said. As for other pollinators, some moths fly at night but most require light and heat they can only get during the day.

“If you can spray at night or early in the morning, just as the sun comes up, or in the evening as the sun’s going down or after it’s gone down, then all the pollinators, they’re home for the night so they’re not going to be exposed to anything when you’re spraying,” Parsons says.

Protective predators

Hoverflies as pollinators have the added benefit of predatory larvae that attack various in-crop pests. However, hoverflies, wasps and some moths and butterflies are not as effective as bees at pollinating. The high number of hoverflies makes up for their lack of performance individually, he adds.

As a field crop entomologist with Agriculture and Agri-Food Canada, Tyler Wist has been an ardent supporter of predatory bugs through his Field Heroes program.

Farmers get both good pollinators and pest management with hoverflies, he said.

“When they’re in there pollinating the crop, they say ‘Hey, there’s some aphids here. I’m gonna lay some eggs and then have these little slug-like offspring that go around and stab aphids to death from their mouth parts, and then suck them dry.’ So super cool that they’re both.”

Bee flies and blister beetles are also predatory. Their larvae feast on grasshopper eggs, Wist says, so supporting their growth is beneficial.

Blister beetle adults can potentially eat leaves, so they’re not as beneficial as some other insect helpers. When they do get into the flower canopy, they are good cross pollinators and their damage is minimal compared to other harmful bugs, Wist says.

If farmers want to attract more beneficial insects, including different bee species, supporting their habitat is just as important as proper pesticide management, he says.

“Wild bees will nest in wooded areas and down in the ground too, so undisturbed ground areas are important for some of those ground nesting wild bees.”

Parsons has focused his research on pollinator habitat.

In a canola field without any wetlands, woodlands or edges, there is no habitat for pollinators, no matter how many flowers and forages there are.

“Most of our pollinators are nesting in the ground, about 70 per cent of them,” Parsons says. “So if there’s no (nearby) area that’s uncultivated … there’s no area for those bees to be nesting.”

Without wetland habitat, including willows, wildflowers or weeds, there is no food or places for insects to overwinter. By leaving the natural environment or planting permanent wildflower patches, producers can see benefits for a long time, Parsons says.

Depending on the crop and type of insects farmers are trying to keep in their fields, spray application timing and type can differ from crop to crop, Wist says.

The post Night spraying for forage pest can spare pollinators appeared first on Grainews.

Taking advantage of that natural behaviour, University of Wyoming scientists have devised a way to control grasshoppers on pastures with smaller volumes of pesticides.

The method is called Reduced Agent and Area Treatments (RAAT), in which farmers apply an insecticide to one strip on a pasture, leaving the adjacent strip unsprayed. That alternating pattern continues across the field, so only half the pasture receives insecticide.

The research shows it’s possible to reduce insecticide by 50 per cent and still kill most of the hoppers.

“You can get 80 to 90 per cent control doing this because grasshoppers do move around and some do move around quite a bit,” said John Gavloski, an entomologist with Manitoba Agriculture.

Gavloski shared information about the RAAT method during a Saskatchewan Ministry of Agriculture webinar on grasshoppers and grasshopper control earlier this spring. The basic idea is that grasshoppers will jump into the treated strips.

“The RAATs strategy is effective for grasshopper suppression because the insecticide controls grasshoppers within treated swaths while conserving natural grasshopper predators in swaths not directly treated,” says a U.S. Department of Agriculture report on grasshopper suppression.

The U of Wyoming scientist who did the research on RAATs provided a similar explanation to Wyoming Livestock Roundup, a weekly publication in the state.

“RAAT takes advantage of the insect’s behaviour,” said Scott Schnell, in 2019. “Nymphs and adults alike move around a lot in search of food, so even if we don’t kill them with the initial application, they will likely move to a treated strip in search of food… Because they eat so much, they will likely consume a plant that has been sprayed.”

A U of Wyoming website explains how farmers can employ the strategy.

One option for spraying a pasture in alternating strips is with an ATV. The vehicles are well suited for the gopher holes and bumpy terrain of a pasture and can be equipped with a sprayer.

The U of Wyoming estimates this approach can reduce costs by 70 per cent compared to blanket coverage because it requires a smaller volume of insecticide and less time to spray the pasture.

Some Canadian ranchers may have experimented with RAATs to control grasshoppers on pastures and some farmers have also used the technique on annual crops, Gavloski said.

“I know, anecdotally, that people have been doing it in wheat, canola and some of our other crops… People think they get good results, but it hasn’t been researched in those crops.

“Unfortunately, this technique has only been (studied) in a pasture/rangeland situation. I’m trying to encourage our researchers to duplicate these experiments in some other field crops… in our Canadian Prairie conditions.”

During the webinar, Gavloski encouraged farmers to control grasshoppers early in the season. Waiting for them to develop into adults is a mistake.

“We don’t want you to get to that point that you’re trying to battle adult grasshoppers. The adult grasshoppers are moving around. You need higher rates… some products don’t work against them.”

A Manitoba Agriculture document contains more information on grasshopper monitoring and management.

It says the nymph stage is the optimal time to kill grasshoppers, before their wings develop.

“Insecticide applications are most effective and the costs are lower … while the nymphs are still concentrated in their breeding areas,” Manitoba Agriculture says.

“It is generally best to control grasshoppers when the majority are in the third to fourth nymph stages. The lowest dosage given on the insecticide label should be used when the grasshoppers are small and the vegetative cover is low.”

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Cereal Aphid Manager helps farmers and crop advisors tackle aphid problems in fields by predicting what aphid populations will be in seven days and the best time to apply insecticide.

The app from Agriculture and Agri-Food Canada is based on a model that treats a grain field as an entire ecosystem by considering many complex biological interactions — including the impact of beneficial insects that help limit aphid populations.

Wist, an AAFC entomologist based in Saskatoon, applied for research funds to update the app in April through the Saskatchewan Ministry of Agriculture’s funding call, where many grower groups that represent farmers participate in funding research.

According to Wist, the money is needed to help ensure Cereal Aphid Manager keeps up with newer technologies. The app, which came out in March 2018, can be used on Apple and Android platforms, but there have been numerous changes in these operating systems since then.

Wist says he knows several grower-funded research groups are interested in helping get the app back up to speed.

“This was built for an older version of Android, for example, so we’re at that point where we need to do a little bit of upgrading,” he says.

Wist hopes to improve Cereal Aphid Manager in several other areas too — including adding canary seed to the app’s list of crops.

He notes two primary cereal aphid pests on Prairie farms are also a problem in canary seed production. Wist and fellow AAFC research scientist Bill May have completed work on determining economic thresholds for controlling aphids in canary seed crops, which they’d like to see incorporated in an updated Cereal Aphid Manager app.

Wist also hopes to enhance an aspect of the app called the dynamic action threshold, which takes into account the pressure insect predators and parasitoids put on aphid populations.

In simple terms, an action threshold is that point where a pest problem is considered serious enough to warrant actions, like insecticide spraying, that can prevent the pest population from causing economic damage.

The dynamic action threshold in Cereal Aphid Manager factors in the number of different natural enemies of aphids that are present in a grain field and how many aphids they can eat or parasitize per day.

“If you’ve got enough predators and parasitoids in your field and they’re there early enough, they can stop an aphid infestation … and you might not have to get in there with your sprayer,” says Wist.

Wist notes there are new pictures and some recent research data on the voracity of aphid predators and parasitoids he’d like to add to the app to increase its effectiveness as a crop protection tool.

Prairie predators and parasitoids

Presenting at the CropConnect conference in Winnipeg in February, Wist shared photos, videos and information about some beneficial insect predators and parasitoids, not just in cereals but in other crops as well, that farmers could see this coming growing season.

READ MORE: Predators and parasitoids – your bug buddies in the field

This includes lady beetles, commonly referred to as lady bugs. This voracious insect will feast on aphids at both the larval and adult stages, making it “a really great predator” in Wist’s eyes.

Wist says there are numerous species of beneficial parasitic wasps in Prairie crop production. These kill pests by injecting them with eggs that produce larvae, which consume their insect hosts from the inside out.

While his research shows only one parasitic wasp species, Aphidius avenaphis, is a significant natural enemy of cereal aphids, Wist notes it can have a sizable impact.

A single female A. avenaphis wasp, for example, can kill up to 25 to 30 English grain aphids in one day, leaving “aphid mummies” with their offspring inside.

Smartphone tools such as Cereal Aphid Manager enable farmers to factor in insect predators and parasitoids in their spray decisions, but as Wist points out, there are other steps they can take to protect beneficial insects.

One is to provide shelterbelts and other areas where beneficial insects can flourish and also take refuge during the colder months. Undisturbed leaf litter at the base of a tree, for example, is the perfect home for lady beetles nestling in for the winter.

Wist says beneficial parasitic wasps feed on nectar, so seeding some areas within or around fields with flowering plant species gives them a place to eat and build up energy to attack aphids and other pests.

Some lady beetle species feed on pollen, he adds, so having flowering spaces around the farm will help sustain beetle populations.

For scouting tips and more information on practices that can help preserve important pest predators and parasitoids, Wist recommends farmers and crop advisors check out the Field Heroes website.

Wist maintains the Field Heroes campaign, launched by the Western Grains Research Foundation in 2017, has contributed a lot to increased farmer awareness of beneficial insects in cropping systems.

How Cereal Aphid Manager works

The Cereal Aphid Manager app, which can be downloaded from the Apple Store or Google Play, is a scouting tool to help grain producers determine whether an aphid population will grow large enough to pose a significant threat to crop production. Users can also access a French-language version at the touch of a button.

Users walk a certain path through a field, which is recommended by the app. It includes a minimum of five stops, at which users count the number of aphid and beneficial insects. To help them identify insects, Cereal Aphid Manager also includes a photo guide.

After completing the recommended path, the app will provide a prediction for whether to spray or not spray, or if and when the user should sample the field again. The recommendation, along with the survey date, is stored on the user’s device to keep track of a field’s aphid population over the course of a growing season.

According to AAFC, it’s important to note winds can spread cereal aphids from the northern United States onto farms in the Canadian Prairies — something Cereal Aphid Manager cannot predict. Because of this, farmers and crop advisors are urged to check their fields regularly during the growing season, regardless of what the app recommends.

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While it’s still too early to say what pest and disease forecasts will look like this season, it’s never too soon to start thinking about temperature and other factors that can help to determine the right — or wrong — time to apply pesticides.

Dan Johnson is a professor of environmental science and researcher with the University of Lethbridge who has studied grasshoppers extensively. He says one common fallacy in fighting the herbivorous pest is that the pyrethroid insecticides that are so effective against them begin to lose their efficacy when temperatures climb above 25 C.

Pyrethroids are a special class of chemical that attack the nervous system of insects. They are fast-acting and especially effective against most chewing insects. They aren’t highly toxic to birds and mammals in most cases.

“The fact of the matter is that for decades it’s been on labels and it’s been on websites … that you shouldn’t spray pyrethroids on grasshoppers above 25 C. There’s never been any evidence that I’m convinced by for that [warning],” he says.

“Something happened long ago that made somebody say the reason it failed was temperature and ever since that’s just been gospel. As far as I can tell it’s false. I’ve seen all kinds of field trials with pyrethroids done under proper experimental conditions that showed no apparent impact from temperature.”

Johnson points out that a large lab study he and technician Craig Andrews conducted in the early ’90s bore that out.

The results of that study showed pyrethroids continue to work effectively at temperatures as high as 27 and 31 C. No temperature resulted in failure and warmer temperatures just resulted in higher grasshopper mortality.

Despite that, most such products continue to carry labels recommending they not be sprayed if the daytime temperature exceeds 25 C.

“As far as I can tell, it was just a mistake made sometime in the ’80s. It’s been there ever since. I have no idea why. It is possible that some rare combination of a certain species and a certain pyrethroid could have a temperature issue, but we have never seen it, and certainly not in the field,” he says.

All that said, Grainews does not recommend or endorse off-label use of any registered crop protection product.

“I’m a big advocate of reading the label and following the label. I think that has to be done,” Johnson says. “But I also think the labels have to be based on science.”

Johnson adds he doesn’t believe any additional research is required on the subject since it has already been studied extensively and there are other subjects that should be made a higher priority.

Scouting by species

Although grasshoppers can have a devastating impact on yield with crops such as wheat, soybeans and corn, most species aren’t considered pests. The two primary pest threats are the two-striped and clear-winged grasshoppers. They can usually be recognized by damage when there are large numbers.

Johnson says that’s why it’s important for farmers and the people they work with to get out into the field and conduct regular scouting to determine what kind of grasshoppers may be present. Even if pest grasshoppers are detected, it’s best to hold off on spraying if they are still hatching since pyrethroids won’t kill any insects that are still below ground. Any active grasshoppers seen during March and April are species that cause no crop or pasture damage.

Damage over numbers

Farmers should bear in mind when scouting for grasshoppers that visible damage, not insect counts, should determine whether to spray. “Visible damage is key, not count,” Johnson says.

“Sometimes I’ve seen 100 (grasshoppers) per square metre that aren’t damaging the crop, oddly enough. Other times, even eight per square metre can damage the crop. It all depends on how old they are, what kind they are, and how hot it is.”

Breakdown

Check out any of the multitude of farm forums available online and you are likely to find dozens of suggestions on when is the best time to spray your fields. One common suggestion is that spraying should be avoided when sunshine is intense and the UV index is high.

Johnson says while it’s true UV rays can influence the way some chemicals interact with plants, their impact on that interaction is quite low. Although some chemicals do break down fairly rapidly under intense sun, the rate for most is not very fast. In addition, most chemical sprays are generally only effective for a couple of days, he adds.

Another popular online theory is that the best time to spray can depend on what kind of chemical mixture you have in your tank. A more complex mix might be best left until later in the day when the sun’s intensity has started to drop, some online commentors post.

Johnson says while that might be true in some cases, most tank mixes remain effective even in extreme conditions.

“Most of these mixes have been tested so we’re sure that they work to kill the pest. It almost never happens that mixing two pesticides together will deactivate one or the other.”

‘Sweet spot’

Jake Ayre helps operate his family’s farm near Minto, Man. where they grow a number of cash crops including wheat and canola as well as operate a pedigree seed business. He also has a Core pesticide applicator license and runs a custom spray business in the area.

Ayre says weather is always top of mind for him when determining whether or not to spray.

“On our farm or when I’m doing custom spraying, I am always checking the weather in-season,” he says. “We have weather stations at our home farm and then we have (another) farm east of our property too … where we have weather stations too.”

His best advice to fellow growers to determine when to spray is to closely read the label of whatever product they are using.

“My first advice would be to always read and check your pesticide labels because as part of the requirement of those pesticides getting registered, they have to give details on applications. There’s a wealth of information there,” Ayre says, adding that provincial crop protection guides are another valuable source of information.

On the subject of when it’s best to spray, temperature-wise, Ayre says for him it can sometimes come down to what is being sprayed. For example, he says glufosinates such as Liberty tend to perform better in higher temperatures with higher water volumes.

Ayre often relies on a metric known as Delta T, an atmospheric moisture parameter first conceived on in Australia that has recently made its way to Canada. It incorporates both temperature and relative humidity data on a graph to determine a “sweet spot” for when is the best time to spray.

That means avoiding spraying when the Delta T is either too high or too low, with a range of two to eight described as ideal. For example, if the temperature is 25 C and the relative humidity is 40 per cent you have a “green light” to spray whereas a temperature of 30 C and 20 per cent relative humidity would be unsuitable for spraying.

Dodging drift

Of course, no discussion about spraying would be complete without a mention of wind. Spraying in windy conditions can lead to drift and a loss of valuable chemical inputs.

Ayre says the general recommendation in most cases is to halt spraying if winds exceed 25 km-h. New spraying technologies, such as air-induced nozzles which can be programmed with exact p.s.i. ratings from the cab, can help reduce drift and in some cases can allow farmers to spray in slightly windier conditions.

Another tool that can come in handy in determining if it’s the right time to spray, says Ayre, is the InputsPro app that can be downloaded to a smartphone or tablet. The subscription-based service collects all of the data from the provincial crop protection guides (including material safety data sheets, rates, application windows and cropping restrictions) and makes it available anywhere, at any time.

Spring survey

Johnson says one tool he would like to see made available to farmers in the Prairies is an annual spring pest forecast. While fall forecasts are already readily available, such information is largely unavailable to farmers in Western Canada.

“I think that would help a lot. In fact, we did it two years ago (in Alberta). What that did was it not only gave a way better view of what was coming a week or two later, but it also gave us a way of testing our predictions, our model development. We need a little more precision of information delivered to farmers.”

The post Spraying facts, fallacies and forethought appeared first on Grainews.

But that doesn’t mean resistance doesn’t happen. Resistance in insects occurs for the same basic reason it does in weeds, says a leading entomologist — the overuse of certain crop protection products.

“People use the same group or products over and over again,” says John Gavloski with Manitoba Agriculture.

“Eventually you will get a very, very small number of individuals that will survive the treatments and they will be genetically different from the susceptible population. They make other progeny containing these mutant genes that prevent the insecticide from killing them. That’s how the population starts to grow over time.”

Although Prairie farmers shouldn’t be complacent (insecticide-resistant insects such as diamondback moths can fly in from other regions, for example), they’re fortunate that insects with resistance aren’t as prevalent as they are in many areas, says Boyd Mori, an assistant professor of agricultural and ecological entomology with the University of Alberta.

“I think we’re lucky in a lot of ways. We have harsh winters. We don’t have many species that have multiple generations per year that require multiple insecticide sprays, which can really contribute to the buildup of resistance.”

Not surprisingly, one of the best ways to avoid resistance is to use as little insecticide as possible. But how do you know those limits?

One of the strongest tools for making that “spray now” decision is an insect’s economic threshold — the point where there’s a sufficient population of the insect to cause yield losses on par with the cost of controlling them. These thresholds, which depend highly on the cost of the control and the value of the crop, can usually be found in the latest editions of provincial crop protection manuals.

“Use the thresholds properly and only spray when an insect is above the threshold,” says Gavloski. “Only using insecticides when necessary is step one because you’re not subjecting the insects to as many treatments and selection pressures.”

Another method is timing foliar insecticide applications for maximum effectiveness. Like economic thresholds, spraying windows differ between species.

Selective insecticides that target specific pests are an option in some cases, says Gavloski. “You have insecticides that target specific insects or groups of insects versus killing all insects. That allows natural biological controls that are out there to survive.”

Crop rotation, when possible, can also be an effective tool. But perhaps the most accessible action is rotating insecticides by their chemical groupings. “If any group has been relied on heavily recently or has recently not been working well, choose an insecticide from another group.”

Sometimes producers will rotate individual insecticides within the same group, in the process increasing resistance to that entire group of products.

“If an insect is resistant to one particular pyrethroid, for example, they’re likely to be resistant not just to the product but the group,” says Gavloski. “Usually, if an insect develops resistance to one of the chemicals in a group, often that resistance transfers to other products within that group just because they kill the insects in very similar ways. That’s quite common.”

Gavloski suggests getting to know the insecticide groups, which can usually be found in provincial crop protection guides and some online fact sheets. He also recommends doing research on any biological controls (such as beneficial insects) and figure out how to manage them, if feasible.

“Any kind of cultural or biological controls that would reduce the number of insecticides are good,” he says.

How to manage confirmed insecticide-resistant insects

Western Canadian agronomists and researchers have confirmed some resistant insect populations for farmers to look out for. These include alfalfa weevil and Colorado potato beetle.

In Alberta, Mori is aware of one insect pest with definitive insecticide resistance — alfalfa weevil in alfalfa seed production in the southern part of the province. These weevils are resistant to Group 3A pyrethroids.

Mori recommends organophosphate products for producers rotating out of the pyrethroids. However, he urges some caution when it comes to using the malathion active ingredient, which falls under the organophosphate umbrella. Although this ingredient has been registered for use on alfalfa weevils in seed production, he says farmer reviews haven’t been great.

“From what I’ve heard, farmers don’t think they have great control with it. It has more to do with the growing conditions though. It’s supposed to be sprayed at above 20 C in low winds. That doesn’t occur that often at the time of year they need to apply the product.”

There’s a semi-selective insecticide available for alfalfa weevil that goes by the trade name Coragen, a Group 28 product.

“It’s registered for suppression of alfalfa weevils and is more selective. It is supposed to be less toxic to bees.” 

Although alfalfa weevil can be managed by rotating out of alfalfa seed crops, it’s not easy, says Mori.

“Alfalfa is a perennial, so these fields are usually two, three or four years of production in the same fields, which allows the alfalfa weevil population to stay within that same site. It’s grown multiple years in the same sites and is usually grown under contract for at least a couple of years. They just can’t rotate out of it easily.

“Right now, in the (alfalfa) seed crops, there’s really not much we can do except rotate modes of action.”

Colorado potato beetle is exceptionally good at developing resistance to insecticides, says Gavloski. Previous studies have found them resistant to one of the most oft-used insecticides on the market — Group 3A (pyrethroid) insecticides. Colorado potato beetle has also been found to have some resistance to Group 1B (organophosphates).

“It’s been a constant battle,” says Gavloski. “We’ve had insecticide resistance in (Colorado potato beetle) in Manitoba and across the Prairies for quite a while. It’s something potato growers have to battle with in any region where potatoes are grown in large acres.”

There are also pockets of resistance to Group 4A (neonicotinoids) developing among the potato-growing regions of the province, says Gavloski. Producers must be particularly careful with products in this group because they’re available as seed treatments, for in-furrow application and as foliar sprays. As a result, producers sometimes make the mistake of overusing this group in potato crops.

“With the neonicotinoids, we caution people that if they put them down in the furrow with the seed, they shouldn’t be following up with a spray because then you’re using two products from the same group in the same year,” he says.

In fact, labels of these products are quite clear on this. “Potato growers should be aware that if a neonicotinoid is used as a seed treatment or in-furrow, the label states, ‘Do not apply any subsequent applications of a Group 4 insecticide,’” he says.

Crop rotation can be an effective tool against potato beetles as it can be used to cause early-season populations of the pest to concentrate at the edge of fields, says Gavloski. Growers can take samples to verify this and, if so, focus product applications in those areas, in the process minimizing insecticide use.

There are some semi-selective insecticides registered for use against Colorado potato beetle in Canada. Some of these go by the trade names Coragen (a Group 28 diamide), Rimon (Group 15 benzoylureas), and Success and Entrust (both Group 5 spinosyns).

High temps can imitate resistance

Sometimes what appears to be resistance isn’t always resistance. A big culprit that can blur these lines is the temperature when foliar insecticides are applied, says James Tansey, provincial specialist of insect/vertebrate management for the Saskatchewan Ministry of Agriculture.

“Producers sometimes put these synthetic pyrethroids down when the weather is really hot and don’t get the effect that they’d like. They sometimes misunderstand that as potential resistance when it’s actually a temperature issue. There are temperature recommendations on product labels and these need to be adhered to.”

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