Features Agronomy Insect Pests
Insect update and forecast 2014

Cutworms take top billing in Alberta in 2013. While insect pressure was low in many areas of Saskatchewan due to the extended winter and cool, wet conditions in the spring, cabbage seedpod weevil and bertha armyworm were significant pests during the growing season. In Manitoba, grasshoppers, cutworms and canola pests took centre stage.  

Pests of all crops
Scott Meers, insect management specialist with Alberta Agriculture and Rural Development (ARD) at Brooks, Alta., says it was an interesting year for cutworms (Noctuidae) in Alberta in 2013. “The major issue occurred very early in the spring with several very badly damaged fields that were attacked by Army cutworm (Euxoa auxillaris). Most of the affected fields were between Lethbridge and Vauxhall. Because these cutworms overwinter as partially developed larvae, they were big enough to cause severe damage very early. Several new alfalfa fields were damaged as was some winter wheat. In all cases the fields had significant growth of weeds or crops the previous fall,” says Meers.

Cutworms were also an issue in northern Alberta near LaCrete in June with black army cutworms in large numbers within a few canola fields that had volunteer alfalfa issues. Hand-collecting near LaCrete also resulted in dingy, glassy/yellow-headed cutworms, which were reared as part of the prairie-wide CARP Cutworm Project. There were reports of pale western (Agrotis orthogonia) and redbacked (Euxoa ochrogaster) cutworms in several locations from central Alberta.

John Gavloski, entomologist with Manitoba Agriculture, Food and Rural Development (MAFRD), says there were some high populations of cutworms reported on cereals in western Manitoba. Some damage was also reported to corn and sunflowers in the eastern, central and southwest regions during June, and cutworms were also a concern in some canola fields with one field reseeded in the Sanford area (central) because of cutworm damage. Cutworm control was also reported on soybeans in central Manitoba.

In Saskatchewan, Scott Hartley, provincial insect specialist with the Ministry of Agriculture, says cutworms were not a serious problem in 2013. After outbreak levels in 2010-11, cutworm populations have been on the decline. As part of a major cutworm research project, the Ministry of Agriculture submitted well over 100 cutworm samples in 2012 and only one in 2013.

Gavloski says there were reports of wireworm (Elateridae) damage to cereal fields from several areas of Manitoba. There was some reseeding of winter wheat in the eastern region because of wireworms. High levels of wireworm damage were also reported in some cornfields in the eastern area.

In Alberta, Meers fielded fewer wireworm reports this year from producers frustrated with poor control of wireworm using registered seed treatments. The problem still hasn’t gone away and many producers are now seed treating but not satisfied with the short-term protection they are getting with current insecticidal seed treatments.

After the high 2012 levels of aster leafhopper (Macrosteles quadrilineatus), the insect vector for aster yellows, levels were low and not a concern in 2013. Hartley says that favourable winds from the south bringing in the leafhoppers were not observed until the latter half of May. This was over a month later than in 2012 and reduced the number of generations and consequential population increase in 2013.

In Manitoba, grasshoppers were a concern in many crops this year, resulting in insecticides being applied to many fields and the edges of fields being treated to prevent them from moving into crops. In Saskatchewan, higher-than-normal grasshopper populations were reported in the northeast in late July near Whitefox and Nipawin. Serious infestations were recorded in parts of the Peace River region. There were many comments on grasshoppers being in higher numbers throughout Alberta and Saskatchewan at harvest.

The risk of economically significant grasshopper populations in Alberta in 2014 has increased in some areas of Alberta and remains stable in most others. Areas indicated with moderate to severe risk could experience problems with grasshoppers if environmental conditions favor the hatching and development of grasshoppers in late May through June. In Manitoba, the grasshopper forecasts show light to moderate risk in the southeast and Winnipeg regions.

The risk for grasshopper infestations in 2014 appears low for most of Saskatchewan based on adult grasshoppers observed during the annual grasshopper survey. However, Agriculture and Agri-Food Canada noted that grasshopper eggs were easily found in the fall egg survey, suggesting there is the potential for increased populations in 2014.

Canola pests
Striped flea beetle once again caused damage in areas of the Peace River region. Flea beetles caused little concern in the balance of Alberta in 2013. In Manitoba, Gavloski reports that the use of seed treatments containing neonicotinoid insecticides to manage early-season flea beetle populations continues to be common. Feeding damage to young plants at or above threshold levels was still reported from all agricultural regions of Manitoba.

“There are reports of some fields being sprayed with insecticides two, three or four times early in the season, and some fields being reseeded because of excess feeding from flea beetles,” says Gavloski.

Flea beetles were not a major pest in most areas of Saskatchewan in the spring of 2013. However, slow growing conditions in the spring caused concern for young seedling canola crops and there were reports of large numbers of flea beetles congregating in canola fields last fall across the Prairies. Since these will be the overwintering generation of beetles that cause damage to seedlings in the spring, it suggests that these insects could be a problem in 2014 in these areas.

The cabbage seedpod weevil (Ceutorhynchus obstrictus) occurred above economic threshold throughout its “traditional” range in southern Alberta, as is the case every year, says Meers. Scouting and spraying are routine management practices for canola producers south of the Trans-Canada Highway. Spraying was common south of Highway 1 in 2013. Initial data from the 2013 survey suggests that cabbage seedpod weevil expanded its range in Alberta into Paintearth and Stettler counties.

In Saskatchewan, cabbage seedpod weevil was a major insect pest in canola in 2013. Hartley says that due to the late seeding and large numbers of weevils, many questions were asked related to timing of chemical application and tank mixing with fungicides for sclerotinia. The most severe infestations were reported in the southwest, as is the case in most years. However, spraying for populations was reported in the south-central region, from northwest of Moose Jaw and south to Assiniboia. Cabbage seedpod weevils were present in fields east of Regina in the 2013 survey (co-ordinated by AAFC) but not at economic levels.

Lygus bugs were once again a problem in canola but less so than in 2012. Southwestern Alberta and the foothills were the areas with the most severe issues. There were reports of a few Manitoba canola fields with economical levels of Lygus bugs in the Eastern region in mid-July.

Bertha armyworm (Mamestra configurata) numbers were monitored in-season across the Prairies. There were some areas of Manitoba that had high levels of larvae of bertha armyworm and insecticides were applied to control them in early August. Most of the insecticide applications for bertha armyworm were in the southwestern regions of Manitoba. Spraying for the bertha armyworm larvae was reported to some degree in most areas of Saskatchewan where canola was grown. Infestations were also reported from the southwest, where bertha armyworm is an uncommon pest. Bertha armyworm also caused damage in pea and flax crops. In Alberta, populations were very high once again in central Alberta, but economically significant populations of larvae were scattered throughout Alberta.

“It is also interesting to note that we checked several fields in Lamont County that had high moth catches, evidence of early feeding on lower leaves but very little to no population later in the season. As the season progressed many reports were made of dead and dying bertha armyworm from what appeared to be both virus and fungal infections,” says Meers. “Bertha armyworm feeding was reported on fababeans in several locations and is certainly something to watch for in the future.”

Growers are reminded to check provincial bertha armyworm forecasts in-season, as pheromone traps are put out throughout the Prairies to help predict risk levels based on adult moth emergence.

Pheromone-baited traps were used to monitor the arrival of diamondback moth (Plutella xylostella) adults from the United States. There appeared to be no favourable winds from the southern U.S. and northern Mexico until the last two weeks of May and diamondback moths were not a major pest in 2013 in Alberta and Saskatchewan. Diamondback moth was controlled in some canola fields in the eastern region of Manitoba.

Hartley says that for the second year in a row, significant swede midge infestations were reported in canola fields in northeastern Saskatchewan near Nipawin and Carrot River. Typical damage was to canola flowers that were infested with swede midge larvae. There was spraying for this pest in 2013; however, there are no reliable recommendations for timing of control for the swede midge. In Ontario, this insect has been a pest of canola and brassica vegetables for several years. In vegetables, multiple insecticide applications are required.

“Due to the multiple generations in a year, the swede midge is difficult to control and multiple applications is not likely a viable economic option in canola. Research is required to determine management recommendations under Prairie conditions,” explains Hartley.

Root maggots (Delia spp.) were common throughout Alberta in 2013 and in some cases very severe damage was observed. It appears the worst damage was on plants in thin stands.

Cereals
Wheat midge (Sitodiplosis mosellana) caused serious damage in the Peace River region near Manning and near Falher. Some head samples showed up to 50 per cent kernel damage. In southern Alberta around Claresholm, some producers did spray and there was not a high level of damage.

“We now perform soil core surveying over the entire province and will process over 300 samples this year. In the last two years, surveying in the Peace River region has expanded to include more sites which will hopefully better represent wheat midge activity within our northern wheat producing region,” says Meers. “In the spring we did an intensive look for parasitoids associated with the larval cocoons and found parasitized midge from Manning and High Prairie, although densities of these beneficial insects were very low.”

The impact of wheat midge was low in Saskatchewan and Manitoba in 2013.

The Alberta 2014 wheat midge forecast indicates a general decrease for midge risk in southern Alberta and a large increase for midge risk in the eastern Peace Region. The Saskatchewan 2014 wheat midge forecast indicates high infestations in the Black and Dark Brown soil zones in eastern regions where the wheat midge is a frequent pest for wheat producers. An area of high midge density is also identified in the north-central region in the Prince Albert area.

Gavloski says armyworm (Mythimna unipuncta) were a concern in some small grain fields in the Ste. Rose and Beausejour areas and some high levels were also reported from the North Interlake. Most of the higher populations of larvae were present in late July and early August. Samples of armyworms collected from the central region for the MAFRD Crop Diagnostic School turned out to be heavily parasitized.

Severity of wheat stem sawfly (Cephus cinctus) damage was lower again in southern Alberta. There are still some areas of concern left in southern Alberta around Foremost. “We have found a few individual fields with slightly higher sawfly cutting levels in our 2013 fall survey that are outside of the core area, maybe part of resurgence. This will be something to watch next year,” says Meers.

Cereal leaf beetle (Oulema melanopus) is established in southern Alberta. The highest densities in 2013 occurred north of Taber in the Vauxhall area. There were several fields sprayed and at least some of them were approaching threshold levels. The cereal leaf beetle also showed up in a couple new areas, one south of Lethbridge and also in the Red Deer-Olds area. The population in the Edmonton area continues to grow with various agrologists reporting cereal leaf beetle larvae. “There is continuing need to maintain relocation programs for its primary parasitoid, Tetrastichus julis,” says Meers.

In 2009, cereal leaf beetle was found in the Swan River Valley of Manitoba, but no “economic” populations of cereal leaf beetle are reported in Manitoba. However, the known range of cereal leaf beetles has expanded to the south and east. In 2013, cereal leaf beetle was found in fields near Brandon, Holland, Treherne, Killarney and Pilot Mound. A biological control program using Tetrastichus julis (Eulophidae), a parasitic wasp, is being implemented to try to control the populations.

In Saskatchewan the cereal leaf beetle has been found in the southwest, near the Alberta border and in the east near Moosomin but no significant infestations have been identified.

Field peas
In 2013, pea leaf weevil (Sitona lineatus) damage was found in the same general area in southern Alberta with no real change in the range since 2007. “Producers have been struggling with deciding to treat their seed or not. Seed treatment is the most effective but much like flea beetles there are years when it doesn’t pay. There are still acres that have foliar treatment even though there is likely not an economic return from doing so,” says Meers.

A feeding damage survey was carried out late May through early June in southern Alberta. There were several reports of pea leaf weevil damage to alfalfa seedling stands. Also, as the acreage of fababeans increases, the pea leaf weevil damage to those fields will need to be monitored closely as fababeans are a strongly preferred host.

In Saskatchewan, Hartley says the range of this insect continues to move eastward in southern regions. The most intensive feeding is in the southwest; but in 2012, feeding notches on pea leaves were noted just north of the South Saskatchewan River. In 2013, evidence of weevil feeding was noted in rural municipalities numbers 228 and 259 (west central region). The eastern edge of the pea leaf weevil range appears to be about midway between Swift Current and Moose Jaw and the southern edge extends to near the U.S. border.

Soybeans
Soybean aphids (Aphis glycines) started to be noted in very low levels in soybean fields in late July in Manitoba. Populations remained very low and there were no reports of high or economical populations for a second year in a row, says Gavloski.

Spider mites started to be noticed in some Manitoba fields in late July and August. In most instances, populations were not economical. However, there was some field border spraying for spider mites in the central region.

Green cloverworms (Hypena scabra) were present in fields of soybeans in the eastern, Interlake and northwest regions of Manitoba. They were generally at levels below economical importance; however, there were some fields of soybeans in the eastern region that were sprayed with insecticide in July because of high levels of green cloverworm.

April 9, 2014  By Bruce Barker

Cereal leaf beetle strips the surface tissue from cereal leaves. Insect update and forecast for 2014 crop year across the Prairies.