Wireworms – We’re Just Seeing the Tip of the Iceberg

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Mature larvae of the Hypnoidus bicolor (top) and Selatosomus destructor, the two most important wireworm pests in the Prairie provinces.

Damage to field crops by wireworms is poised to escalate across the Prairies. Neil Whatley, crop specialist at Alberta Agriculture and Forestry, explains how producers can be proactive about finding solutions in their areas by submitting samples to Canada’s wireworm research team.

“Lindane insecticide, such as Vitavax Dual, etc., kept wireworm numbers low for several decades on the Prairies,” says Whatley. “Since the ban of this organochlorine pesticide in 2004, wireworm damage in field crops is rebounding. Some researchers say we’re just seeing the tip of the iceberg.”

“Varying from region to region, around 30 different pest wireworm species exhibit diverse behaviours and lifecycles, making a single control measure improbable,” explains Whatley. “An individual region may contain more than one wireworm species.”

Depending on the species, the worm-like larvae can feed on plant roots and germinating seeds for up to 3 to 5 years before developing into the adult click beetle stage. Adds Whatley, “While current seed treatments may repel wireworms for a growing season, their populations continue to increase, and these treatment measures begin to fail.”

Due to their preference to eat annual or perennial grasses, wireworm populations can build up in fields that have extended periods of cereal crops or pasture. Pulses, oilseeds, potatoes and sugar beets are susceptible to wireworm damage when grown in rotation with cereals. Crops grown in recently broken sod are especially vulnerable. Non-farmed areas like grassy ditches and undisturbed field borders also harbour wireworms and click beetles.

Agriculture and Agri-Food Canada’s (AAFC) wireworm research team is identifying wireworm species and researching new control measures. “The research team needs to know which specific wireworm species dominates in your farming region so the correct control option(s) can be applied as the problem worsens,” explains Whatley.

Dr. Haley Catton, cereal crop entomologist with AAFC, is the prairies representative on the team and based at the Lethbridge Research and Development Centre. The team is asking for producers to submit wireworm samples from their fields.

“Due to a greater amount of soil moisture, wireworms migrate near to the soil surface in early spring when soil temperatures rise above 5 C, making spring the best time to bait and capture wireworms,” adds Whatley. “Baiting can be as simple as burying a cup of a cereal-based product like flour, bran or wheat seeds to a depth of four to six inches, or 10 to 15 cm, into the soil at marked locations.”

Dig up the baits 10 to 14 days later, collecting the wireworms and some of the not too wet field soil. Insert the sample into a hard plastic container for shipping. There may be more than one species present, so collect as many wireworms as possible.

Mail your wireworm sample to:

Dr. Haley Catton
Agriculture and Agri-Food Canada
Lethbridge Research and Development Centre
5403 – 1 Ave S
Lethbridge, AB T1J 4B1

Include a brief description of when and where the sample was collected (nearest town or address), information about the crop rotation in the sampled field over the past 4 years, name and telephone number. Once the species are identified, producers will be contacted with the results.

For more information about submitting wireworm samples, contact Haley Catton at 403-317-3404.

Monitor for Insect Pests this Growing Season

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Pea leaf weevil and feeding damage on field pea. (Photo: Shelley Barkley, AAF)

Specialists at Alberta Agriculture and Forestry (AF) are working to have fields predetermined for the 2018 insect survey season and are looking for assistance from agrologists and producers across Alberta.

This year, the survey teams would like to check pea and wheat fields. They will survey for pea leaf weevil in late spring and survey for wheat midge and wheat stem sawfly in the fall after harvest.

“In addition to the rest of the province, we are looking for pea fields up into the Peace Country because the pea leaf weevil has been confirmed into that area, and we want to expand our survey there,” says Scott Meers, insect management specialist with AF. “We are looking for fields that producers would be happy to have us check. For allowing us on their fields, we will provide those producers with a report of the survey results.”

Meers would also like to increase in the number of bertha army worm traps in Alberta. “We are trying to get four to five traps per county across the province. If you are interested, we will hook you up with all the materials you will need.”

For agrologists and producers who have monitored for the bertha army worm adults in the past, now is a good time to check those traps to see if they need to be repaired or replaced. “They are plastic, and plastic in the wind and sunshine tends to break down after time. Let us know if they need to be upgraded or replaced,” adds Meers.

For more information about monitoring for the upcoming growing season or replacing traps, contact Shelley Barkley at [email protected].

Blackleg and Clubroot in Canola

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Field with heavy clubroot incidence (note reduced flowering in the foreground). (Photo courtesy S.E. Strelkov, UofA)

Blackleg and clubroot are both serious diseases that are growing in severity across Alberta, but with proper and diligent management by all farmers, they can be effectively controlled.

Blackleg

Blackleg is a fungal canker or dry rot that results in stem girdling and lodging. The disease has been present in canola fields since the 1980s.

Today, the availability and use of canola cultivars with resistance to blackleg has helped to avoid significant damage, notes Michael Harding, a research scientist with Alberta Agriculture and Forestry (AAF). However, it is still very common to see blackleg in canola crops.

When blackleg-infected seed is sown, the seedlings that emerge may be infected with lesions on the seedling leaves or stems.
(Photo courtesy Michael Harding, AAF)

Harding and his colleagues have undertaken recent surveys for blackleg (and stem rot) on Alberta canola. In 2016, they found that of 480 canola fields, 432 of them had blackleg symptoms. Indeed, Harding states “the prevalence of blackleg in Alberta has been measured at 55 to 99 per cent in the six surveys conducted over the past eight years. Prevalence was slightly lower in 2017 compared with 2016, as it was a relatively dry year in comparison.”

Long-term survey trends show the pathogen to be present throughout the province, and Harding does not believe any area or farm should consider itself “blackleg free.” Some fields experience little to no loss due to blackleg while others may have significant disease pressure, and he says economic loss experienced by individual farms depends on their location in the province, local weather and field history, as well as cropping and disease management practices.

“Blackleg is always a risk for canola producers and blackleg management practices should be proactive,” Harding says. “Crop rotation (one host crop every four years) is a very effective way to keep disease pressure from building. The pathogen does not survive in soil without a host. So, once the canola residues are decomposed, there is little to no risk of economically-damaging blackleg pressure originating within that field.”

Harding also notes that genetic resistance in the MR- and R-rated canola cultivars is keeping disease severity very low in most fields, as was seen in the survey data. However, Ralph Lange Team Lead Crop Pathology and Molecular Biology at InnoTech Alberta, notes there are now yearly cases of severe loss in cultivars labelled “resistant,” a significant change from the 1990s and 2000s that indicates the pathogen is adapting.

Lange says there are about eight different blackleg strains in Western Canada, and in Alberta, about 80 per cent of all isolates belong to just three strains.

“We continue to have good resistance genes available, and what’s changed is that we now need to actively manage the crop resistance genes we present to blackleg fungus populations,” he explains. “So, frequent and accurate scouting with excellent record keeping is essential for determining if the genes we’re presenting are working or not. Then, producers need to eliminate the non-functioning resistance genes when selecting which canola cultivar to plant (at least one functioning resistance gene).” This is now much easier, Lange notes, because seed companies are starting to reveal which genes are in which cultivar.

Another tool for blackleg management is fungicides. Harding notes while all certified canola seed is cleaned and treated to make it essentially blackleg-free (although infection can still occur due to spores being released from infected stubble), in high-risk situations during the growing season, foliar fungicides may be applied at the one-to-three leaf stage.

Going forward, Harding says the risk of resistance-building in the pathogen is very real when crop rotation recommendations are ignored, especially in wetter years when blackleg has a better chance to infect and cause disease.

“If genetic resistance were to erode due to selection of virulent pathotypes of the fungus, it would have a devastating impact in areas where genetic resistance was no longer effective,” he notes. “While we are not currently seeing widespread changes in blackleg severity, it has been seen in some individual fields. This is a warning sign that we need to think carefully about crop rotation practices and resistance stewardship in order to stay ahead of blackleg.”

Clubroot

In canola, this soil-borne fungus-like disease causes swellings to form on the roots, ultimately stunting the plant and even causing premature plant death. Infection and severity are supported by warm, moist, acidic soil.

University of Alberta scientists and staff from Alberta Agriculture and Forestry currently conduct yearly clubroot surveys, which began in 2003 when clubroot was first identified in the province. The 2016 survey found 289 new clubroot-infested fields and the 2017 survey another 301.

“What we’ve found is that clubroot is spreading fairly rapidly for a soil-borne plant pathogen, and this seems to be due mainly to the movement of infested soil and machinery,” explains Stephen Strelkov, professor in the faculty of Agricultural, Life and Environment Sciences at the University of Alberta. “We’ve also found significant numbers of spores in wind-blown dust from infested fields which could contribute to local spread.”

There is a continued spread eastward, he adds, with several new infestations recently found near the Saskatchewan border.

“Part of why it often takes a few years for growers to ‘up their game’ when dealing with clubroot is because the impact on yield is often very slight,” notes Dan Orchard, agronomy specialist with the Canola Council of Canada. “It’s almost always found in a patch at the field entrance, and the overall field yield isn’t really affected. But if not managed, that patch will become much, much larger and potentially cause total loss of the entire crop.”

Severe clubroot pulled from infested soil (note wilting of plants in the background).
(Photo courtesy S.E. Strelkov, UofA)

At least 12 new strains of clubroot have been identified in Alberta since 2013, and they are all capable of overcoming the resistance in many clubroot-resistant canola varieties.

“In 2016, these strains were confirmed in over 60 fields in Alberta, and in 2017, we identified another 42 fields with potential resistance issues,” Strelkov notes. “These new strains have likely emerged as a result of cropping of clubroot-resistant canola in short rotation in fields with moderate to severe clubroot infestations.”

Orchard notes while best management strategies make a big difference, they are difficult to deploy. “This would include equipment sanitation, which growers have suggested could be hours and hours per piece of equipment for each field,” he says. “Not cleaning equipment is a risk growers seem to be accepting, although I believe many or most of them make sure equipment from unknown regions or potential clubroot regions is clean before entering their lands, which is a great practice to follow.”

He adds there is evidence around the world and preliminary evidence in Alberta suggesting pH plays a major role in clubroot spread and severity.

“Liming fields could reduce clubroot impact, but it’s another excellent management strategy that’s easier said than done,” Orchard says. “I’m convinced, however, that over the next few years and with the help of new technology, the industry will produce better lime recommendations, better pH mapping, better application techniques, and just a better understanding of lime and the benefits/challenges.”

While he believes genetic resistance is currently the most significant factor in keeping this disease at bay, the fact that new clubroot strains are quickly appearing means growers need to deploy a multi-pronged approach.

“The recipe for success would seem to be liming badly-infested patches and seeding them to a perennial grass until spore loads are manageable, coupled with planting resistant canola varieties and rotating sources of resistance on top of crop rotation.”

Strelkov agrees that with the new strains appearing, it’s unwise to use resistant canola varieties as a sole management strategy. He stresses longer rotations are important, and adds while “sanitation often is not viewed as practical, even steps such as trying to remove large chunks of soil from machinery or working infested fields last can be helpful.”

Wheat Midge Tolerance Gene Detected in Soft White Wheat

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Through recent advancements in marker technology, SeCan recently discovered that the majority of the soft white wheat varieties grown in Western Canada contain the Sm1 trait for midge tolerance – and for this reason they will require stewardship. The Midge Tolerant Wheat Stewardship Team provides the background and an explanation of why stewardship is necessary:

Sm1, the only known gene that confers tolerance to wheat midge, was first identified in soft red winter wheat varieties. In the late 1990s, Canadian public breeders worked to cross this naturally occurring trait into red spring wheat (CWRS and Extra Strong) for the benefit of western Canadian producers. These first products were launched in spring 2010 (AC Unity VB, AC Goodeve VB, AC Glencross VB).

Since that time, over 20 varieties of Midge Tolerant Wheat have been registered in many classes, including CWRS, CPSR, CWES, CWAD, and GP/SP.

As Sm1 products neared commercialization, entomologists agreed that the risk of midge becoming resistant to the trait was highly likely. They suggested a stewardship plan incorporating an interspersed refuge (10 per cent of a susceptible variety) was necessary to preserve the useful life of the Sm1 trait.

First evidence of Sm1 in soft white spring (SWS) wheat varieties came from field tests from the General Purpose Co-op during the 2015 growing season – conducted by the Agriculture & Agri-Food Canada (AAFC) Manitoba wheat midge program (Curt McCartney and Sheila Wolfe), and the University of Manitoba midge program (Alejandro Costamagna, Ian Wise, and Roxanne Georgison). These varieties were identified as midge resistant based upon dissection of wheat spikes.

In 2016, in coordination with SWS Breeder Dr. Harpinder Randhawa, the entire SWS Co-op was tested. The data was all based on dissection of spike samples from the Co-op field tests.

Also, in 2016, Dr. Curtis Pozniak from the Crop Development Centre (CDC) at the University of Saskatchewan, tested a marker for Sm1 on

Wheat Co-op entries. This was done to see if his DNA marker accurately predicted the field-based phenotype (i.e. kernel damage).

The DNA marker developed by CDC was done in conjunction with researchers at AAFC. To date, the marker results appear to match the results from the spike dissections.

Based on the work above, the following varieties carry Sm1 and are midge tolerant: AAC Awesome (CWSP), AAC Chiffon, AAC Indus and AC Sadash. AAC Paramount is suspected to carry Sm1 but needs to be confirmed by field test in 2017.

AC Andrew has been tested by marker and in the field, and does not contain Sm1. For this reason it will be an appropriate refuge for all tolerant varieties.

Why Stewardship Now?

If Sm1 varieties have been grown in other regions without a refuge, why do we need a refuge in Western Canada? Other regions, such as the UK and Eastern U.S., do not have a large acreage of wheat in rotation. In Western Canada, the traditional fit for SWS wheat was the irrigation area of southern Alberta – this area typically has little to no midge pressure. However, in the last seven to eight years, we have seen growth in soft white acres into non-traditional areas to supply the feed and ethanol market. In comparison to other classes, the SWS acres are relatively small. This is fortunate, but still needs to be addressed.

The fact we have been growing SWS without a refuge puts the Sm1 trait at risk. Midge tolerant wheat saves producers $40-60 million per year ($36 per acre). There are no replacement tolerance genes. “There is No Plan B.”

For this reason we need to act as quickly as possible to put a stewardship plan in place for the benefit of all wheat producers (not just soft white).

The Stewardship Plan

Seed growers will add refuge to all future seed stocks released of AAC Awesome, AAC Paramount (once field results confirm resistance), AAC Indus, AAC Chiffon and AC Sadash.

Varieties that have not yet been released have limited volumes. Remediation will be a much greater challenge for a variety like AC Sadash that is currently grown on several hundred thousand acres, making up over half of the total SWS acres.

For AC Sadash there were two options to protect Sm1: 1) Work with SeCan members and the industry to add refuge to all seed stocks available, as soon as realistically possible; 2) Deregister AC Sadash to remove it from the system, and replace it with the new products that have refuge blended in.

SeCan has decided it is in the best interests of the industry that AC Sadash remain available – and trust the industry will be willing to participate in implementing a stewardship plan.

The hope is that growers will “do what is right” to protect the trait for the benefit of future generations of wheat producers.

How Can You Prevent Creating Resistance?

If you grow one of these SWS varieties, add a refuge: one bushel of AC Andrew to every nine bushels of tolerant SWS variety.

If you’re unable to add the refuge, spray insecticide to eliminate the possibility of resistant midge (until you are able to add refuge).

In the near future, we hope to have the Sm1 marker commercially available. This will give us the opportunity to monitor farm level samples of AC Sadash for the appropriate level of refuge to ensure the stewardship is being followed.

Heightened Risk from Pea Leaf Weevil in 2017

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Pea leaf weevil and feeding damage on field pea. (Photo: Shelley Barkley, AAF)

Research shows that treating pea seed with a systemic insecticide product is the most effective control measure to prevent pea leaf weevil damage.

According to a crop specialist with Alberta Agriculture and Forestry, properly inoculated annual legume crops, such as field pea and faba bean, produce most of the nitrogen they require for growth through the growing season via nitrogen fixation carried out by nodules on plant roots.

“Hence, field pea and faba bean are generally grown on nitrogen deficient soil without much, if any, additional synthetic nitrogen fertilizer,” says Neil Whatley. “When the pea leaf weevil insect pest feeds on the nodules of pea and faba bean seedlings, this natural nitrogen source is greatly compromised, inhibiting optimal pea and faba bean growth throughout the remainder of the growing season as well as decreasing crop yield.”

The pea leaf weevil was reported in southern Alberta in 1997 and remained for several years south of Hwy 1. Since 2013, this insect’s geographic range has greatly expanded into central Alberta, extending as far north as Sturgeon County, north of Edmonton, with lower levels of feeding reported in east central Alberta.

“Given that 2016 survey levels were high in the aforementioned areas, there’s a high risk of infestation in the same areas if winter and spring conditions are favourable,” notes Whatley. “A potential predictor of population increase is precipitation in August. As many areas with high weevil populations in 2016 experienced August precipitation, pea and faba bean producers in these areas are advised to plan control strategies for the 2017 crop year.”

Feeding damage on faba bean. (Photo: Shelley Barkley, AAF)

After spending the winter as an adult beetle in perennial legumes, adults are attracted to annual and perennial legume crops in spring, including field pea, faba bean, lentil, alfalfa and bean. “However, egg laying only takes place in soil near field pea or faba bean seedlings, so root nodules of lentil and alfalfa, for example, are not affected. Just prior to egg laying, adult pea leaf weevil insects feed on the margins of seedling leaves resulting in a notched or scalloped leaf appearance, which is not expected to reduce yield. After hatching from eggs, the worm-like larvae proceed downward into the soil where they primarily feed on root nodules resulting in decreased nitrogen fixation by pea and faba bean plants.”

Spring weather conditions can alter the timing and severity of pea leaf weevil damage, says Whatley.

“Weevils arrive early to pea and faba bean fields if warm temperatures above 20 C persist for more than a few days in late April or early May, potentially corresponding with higher yield losses. Alternatively, if cool weather occurs during the same period, yield is generally not as compromised, especially when the crop advances past the sixth node stage before the weevils arrive. In either case, field scouting is required to make control decisions on a field by field basis. It’s also advised not to seed into cold soil.”

Yield losses may occur when there are more than 30 per cent of seedlings (three out of 10 plants along a seed row; assess groups of 10 plants in multiple rows) with feeding damage on the clam leaf before the sixth node stage in peas. The clam leaf is the most recently emerged leaf.

“Most research hasn’t shown that control of weevils using foliar insecticide prevents yield loss. The ineffectiveness of foliar spraying probably arises because weevils have already laid enough eggs to significantly damage root nodules when sprays are applied or because healthy weevils immigrate after spraying,” says Whatley. “According to research on the Prairies, nodule protection is more effective when pea seed is treated with a systemic insecticide product prior to seeding. Faba bean may be similarly protected, but this requires investigation.”

If feeding damage is only apparent on the older, lower leaves and not on the newer clam leaf, says Whatley, the weevil has probably already laid eggs and spraying would be of no value.

“As such, producers should scout for damage on the clam leaf and not on lower leaves. Since pea leaf weevils migrate into field pea and faba bean fields, foliar damage is initially observed along field edges. Foliar insecticides applied early in an infestation to field edges may be a sound economic decision; however, additional on-farm research will provide more clarity.”

Whatley adds limited spraying would also reduce the risk of affecting beneficial species, such as ground beetles, that may help manage pea leaf weevil populations through predation.

2017 pea leaf weevil forecast