Week 12 and our staff continue with surveying! This week, more warm weather continues to advance both insect and plant development. Some southern areas of the prairies are preparing to initiate harvest for their earliest crops and are carefully watching moisture meters! If you missed it, in Week 11 we thanked the many people who are busy monitoring in fields across the Canadian prairies!
TEMPERATURE: This past week (July 11 – 18, 2021) the prairies continued to experience above-average temperatures and extremely dry conditions. The warmest temperatures were observed across southern and central regions across all three prairie provinces (Fig. 1. Across the prairies, the average 30-day (June 19 – July 18, 2021) temperature was almost 4 °C warmer than climate-normal values. The warmest temperatures were observed across southern Alberta and western Saskatchewan (Fig. 2). The 2021 growing season (April 1 – July 18, 2021) has been 1.5 °C warmer than average. The warmest temperatures have occurred across southeastern Manitoba, west-central Saskatchewan and southern Alberta (Fig. 3).
PRECIPITATION: This past week significant rainfall was reported across the Peace River region (Fig. 4). Rainfall amounts for the period of June 19 – July 18 (30-day accumulation) have been well below average with most of the prairies receiving less than 40 % of the average amount for this time period (Fig. 5). Growing season precipitation has been less than average across most of the prairies. Western Saskatchewan and most of Alberta have received less than 100 mm of rain this year (Fig. 6).
Model simulations were used to estimate grasshopper (Melanoplus sanguinipes) development as of July 21, 2021. Above-average temperatures in late June and July continue to result in a noticeable increase in grasshopper development. Last week, simulations indicated that most of the population was expected to be in the 4th or 5th instar stages.
This week, grasshopper populations are predicted to be mostly 5th instar (35 %) and adult (35 %) stages (Fig. 1). As a point of comparison, grasshopper development based on long-term average values for this week are 11 % (5th Instar) and 1.4 % (adults) (Fig. 2).
Adults should be present across all three provinces and the occurrence of adults is well ahead of long-term average values (Figs. 3 and 4). The model predicts that oviposition should have begun across the southern prairies (Fig. 5).
Grasshopper Scouting Steps: ● Review grasshopper diversity and scouting information including photos of nymphs, adults, and non-grasshopper species to aid in-field scouting and accurately apply thresholds for grasshoppers. ● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin. ● Start at one end in either the field or the roadside and walk toward the other end of the 50 m, making some disturbance with your feet to encourage any grasshoppers to jump. ● Grasshoppers that jump/fly through the field of view within a one-meter width in front of the observer are counted. ● A meter stick can be carried as a visual tool to give perspective for a one-meter width. However, after a few stops, one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance. ● At the endpoint, the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure. ● Compare counts to the following damage levels associated with pest species of grasshoppers: 0-2 per m² – None to very light damage 2-4 per m² – Very light damage 4-8 per m² – Light damage 8-12 per m² – Action threshold in cereals and canola 12-24 per m² – Severe damage 24 per m² – Very severe damage For lentils at flowering and pod stages, >2 per m² will cause yield loss. For flax at boll stages, >2 per m² will cause yield loss. ● More practically, the following thresholds are offered but, in the event of additional crop stress (e.g., drought), the use of “may be required” versus “control usually required” requires careful consideration:
Diamondback moths (DBM; Plutella xylostella) are a migratory invasive species. Each spring adult populations migrate northward to the Canadian prairies on wind currents from infested regions in the southern or western U.S.A. Upon arrival to the prairies, migrant diamondback moths begin to reproduce and this results in subsequent non-migrant populations that may have three or four generations during the growing season.
Model simulations to July 18, 2021, indicate that the third generation of non-migrant adults are currently emerging across the Canadian prairies (Fig. 1). Compared to long-term average data (climate normal), an additional generation of DBM are predicted to develop during the 2021 growing season!
Monitoring:Remove plants in an area measuring 0.1 m² (about 12″ square), beat them onto a clean surface and count the number of larvae (Fig. 3) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
The economic threshold for diamondback moth in canola at the advanced pod stage is 20 to 30 larvae/ 0.1 m² (approximately 2-3 larvae per plant). Economic thresholds for canola or mustard in the early flowering stage are not available. However, insecticide applications are likely required at larval densities of 10 to 15 larvae/ 0.1 m² (approximately 1-2 larvae per plant).
The recent warm temperatures have contributed to the rapid development of wheat midge populations. Where present, wheat midge populations should be predominantly in the egg and larval stages (Figs. 1 and 2). Last week the model predicted that 51 % of the population would be eggs. This past week eggs have transitioned to the larval stage and wheat midge populations will be primarily in the larval stage (54 % of the population). Larvae will be in wheat heads, feeding on developing kernels.
The model was projected to August 3 to determine potential development at Regina (Fig. 3), Lacombe (Fig. 4), and Grande Prairie (Fig. 5) over the next two weeks. Development is similar for each location. Results indicate that larvae (Sm L1-2) are expected to complete development by the end of July, at which time they will drop to the soil and develop into larval cocoons (overwintering stage).
Monitoring:The window for scouting and application of the economic threshold for wheat midge (i.e., during the synchrony between wheat anthesis and midge flight period) has now drawn to a close for 2021.
Wheat midge was featured as the Insect of the Week in 2021 (for Wk07). Be sure to also review wheat midge and its doppelganger, the lauxanid fly, featured as the Insect of the Week in 2019 (for Wk11) – find descriptions and photos to help with in-field scouting! Additionally, the differences between midges and parasitoid wasps were featured as the Insect of the Week in 2019 (for Wk12). Remember – not all flying insects are mosquitoes nor are they pests! Many are important parasitoid wasps that actually regulate insect pest species in our field crops OR pollinators that perform valuable ecosystem services!
More information about wheat midge can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”. View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.
Thrips in canola (Thynsanoptera) – While scouting at this time of year, curled canola pods may be encountered. The culprits are quite possibly thrips.
Damage: Flower thrips (Thysanoptera) are pests of a broad range of plants including cereals and broadleaved crops such as canola. Thrips are minute, slender-bodied insects with rasping-sucking mouthparts and feed by rasping the surface of canola buds and sucking up plant fluids.
Biology: Thrips have six life stages: egg, two larval stages, a prepupal and pupal stage and an adult. Both adults and nymphs cause damage by feeding on the flower and buds. Limited surveys in 1999 in Saskatchewan and Alberta indicated that the predominant species were Frankliniella tritici (flower thrip) followed by Thrips tabaci (onion thrip) and T. vulgatissimus (no common name).
In canola, pods damaged by thrips are often curled and tend to drop prematurely. Some species, such as T. vulgatissimus have been credited with contributing to pollination.
On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.
Lygus bugs are polyphagous (i.e., feed on plants belonging to several Families of plants) and multivoltine (i.e., capable of producing multiple generations per year). Both the adult (Fig. 1) and five nymphal instar stages (Fig. 2) are a sucking insect. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. In canola, lygus bugs feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.
Scouting tips to keep in mind: Begin monitoring canola when it bolts and continue until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.
Sample the crop for lygus bugs on a sunny day when the temperature is above 20 °C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180 ° sweeps. Count the number of lygus bugs in the net. Sampling becomes more representative IF repeated at multiple spots within a field so sweep in at least 10 locations within a field to estimate the density of lygus bugs. In fact, sampling is most accurate when repeated at a total of 15 spots within the field. Samples can be taken along or near the field margins. Calculate the cumulative total number of lygus bugs and then consult the sequential sampling chart (Figure 3).
If the total number is below the lower threshold line (Fig. 3), no treatment is needed. If the total is below the upper threshold line, take more samples. If the total is on or above the upper threshold line, calculate the average number of lygus bugs per 10-sweep sample and consult the economic threshold tables (Tables 1 and 2).
The economic threshold for lygus bugs in canola covers the end of the flowering (Table 1) and the early pod ripening stages (Table 2). Once the seeds have ripened to yellow or brown, the cost of controlling lygus bugs may exceed the damage they will cause prior to harvest, so insecticide application is not warranted. Consider the estimated cost of spraying and expected return prior to making a decision to treat a crop.
Remember that insecticide applications at bud stage in canola have not been proven to result in an economic benefit in production. The exception to this is in the Peace River region where early, dry springs and unusually high densities of lygus bug adults can occasionally occur at bud stage. In this situation, high numbers of lygus bugs feeding on moisture-stressed canola at bud stage is suspected to result in delay of flowering so producers in that region must monitor in fields that fail to flower as expected.
Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English or French versions are available.
Monitoring is already underway for cabbage seedpod weevil (CSPW; Ceutorhynchus obstrictus) in southern areas of the prairies – it was the Insect of the Week for Wk08! There is one generation of CSPW per year and the overwintered adult is an ash-grey weevil measuring 3-4mm long (e.g., lower left photo). Mating and oviposition are quickly followed by eggs hatching within developing canola pods (e.g., lower right photo). The highly concealed larvae feed within the pod, consuming the developing seeds.
Begin sampling when the crop first enters the bud stage and continue through the flowering.
Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location.
Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field.
Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur.
An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts).
Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators.
High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season, these new adults migrate to overwintering sites beyond the field.
Albertan growers can report and check the live map for CSPW posted by Alberta Agriculture and Forestry (screenshot provided below for reference; retrieved24Jun2021).
Provincial insect pest monitoring networks in Manitoba, Saskatchewan and Alberta are now compiling cumulative counts of adults intercepted from the pheromone-baited green unitraps deployed in fields across the prairies. Review the Provincial Insect Pest Report Links to find summaries or link to the latest bertha armyworm moth counts by clicking the appropriate province’s reporting info for Manitoba, Saskatchewan or Alberta. So far, interception counts remain mainly in the “low risk” categories across the Canadian prairies. Review the 2020 pheromone trapping cumulative moth counts here to identify potential high risk areas to target for scouting for larvae now!
The following is offered to help predict when Culex tarsalis, the vector for West Nile Virus, will begin to fly across the Canadian prairies. This week, regions most advanced in degree-day accumulations for Culex tarsalis are shown in Figure 1 but the unusual heat across the prairies greatly accelerated mosquito development!
As of July 18, 2021 (Fig. 1), C. tarsalis development continues to be most advanced in southern Manitoba, southern Alberta, and southwestern Saskatchewan. Outdoor enthusiasts falling within areas highlighted red (i.e., areas that have accumulated sufficient heat accumulation for C. tarsalis to emerge) should wear DEET to protect against WNV! Because of the continued high temperatures, areas highlighted yellow or orange in the map below (as of July 18) should also start to use DEET this week! IF C. tarsalis is present in an area where WNV is active, it may take as little as 14 days for adults to become fully infective with the current warm weather (Fig. 2).
The Public Health Agency of Canada posts information related to West Nile Virus in Canada and also tracks West Nile Virus through human, mosquito, bird and horse surveillance. Link here to access their most current weekly update (reporting date June 21, 2021; retrieved July 22, 2021). The screenshot below (retrieved 22Jul2021) serves as a reference and reports one human case of WNV in Ontario.
Anyone keen to identify mosquitoes will enjoy this pictorial key for both larvae and adults which is posted on the Centre for Disease Control (CDC) website but sadly lacks a formal citation other than “MOSQUITOES: CHARACTERISTICS OF ANOPHELINES AND CULICINES prepared by Kent S. Littig and Chester J. Stojanovich” and includes Pages 134-150. The proper citation may be Stojanovich, Chester J. & Louisiana Mosquito Control Association. (1982). Mosquito control training manual. pp 152.
Before the harvest rush begins, start to consider pre-harvest intervals. The PHI refers to the minimum number of days between a pesticide application and swathing or straight combining of a crop. The PHI recommends sufficient time for a pesticide to break down. PHI values are both crop- and pesticide-specific. Adhering to the PHI is important for a number of health-related reasons but also because Canada’s export customers strictly regulate and test for the presence of trace residues of pesticides.
The Insect of the Week (IOTW) was originally launched as a tool to promote field guides affiliated with PPMN Network participants and to highlight entomological species occurring in field crops across the Canadian prairies. Almost immediately, the IOTW became one of the most popular ways PPMN shares information related to insect pests, beneficial arthropods AND the entomologists who study them. A surprising array of IOTW posts are available from 2015 to the present and remain available for review and to support scouting and identification – check them out!
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
MANITOBA’SCrop Pest Updates for 2021 are now available – access the July 21, 2021 report here. Be sure to bookmark their Crop Pest Update Index to readily access these reports! Bookmark their insect pest homepage to access fact sheets and more! • Bertha armyworm pheromone trap monitoring update for MB – Cumulative counts arising from weekly data are available here. Cumulative counts are categorized as “low risk” so far (i.e., 0-300 moths). • Diamondback moth pheromone trap monitoring update for MB – Trapping has drawn to a close for 2021. Access the summary here. Only 65 traps intercepted moths and the highest cumulative count was 171 moths near Selkirk. Access the summary (as of June 30, 2021). At this point, in-field scouting for larvae remains important.
ALBERTA’SInsect Pest Monitoring Network webpage links to insect survey maps, live feed maps, and insect trap set-up videos and more. There is also a Major Crops Insect webpage. The new webpage does not replace the Insect Pest Monitoring Network page. Remember, AAF’s Agri-News occasionally includes insect-related information or Twitter users can connect to #ABBugChat Wednesdays at 10:00 am. • Wheat midge pheromone trap monitoring update for AB – Cumulative counts arising from weekly data are available so refer to the Live Map. • Cabbage seedpod weevil sweep-net monitoring update for AB – In-field counts can be entered here to populate the Live Map. Some sites in southern Alberta are reporting densities at or above the economic threshold in canola (22Jul2021). • Bertha armyworm pheromone trap monitoring update for AB – Cumulative counts arising from weekly data have begun so refer to the Live Map. Cumulative counts throughout the province report “low risk” numbers of moths so far (22Jul2021). • Diamondback moth pheromone trap monitoring update for AB – Trapping has drawn to a close for 2021. Refer to the Live Map which reports extremely low numbers of moths intercepted so far (<50 province-wide as of 01Jul2021). At this point, in-field scouting for larvae remains important. • Cutworm reporting tool – Refer to the Live Map which now reports seven sites with cutworms (as of 01Jul2021).
Native to Europe, pea aphids were discovered in Ontario during the late 1800s and continued west into the Prairie region. True to their name, pea aphids consume legumes like field peas, alfalfa, broad beans, chickpeas, lentils and clover. Overwintering as eggs on perennial legumes like alfalfa and clover, pea aphids reproduce asexually until winged females migrate to summer crop hosts to generate several new generations over the growing season.
Pea aphid damage to peas occurs when the insects feed during the flowering and early pod stage, resulting in reduced crop yield due to delayed seed formation and smaller seed size. In alfalfa crops, pea aphids feed on the stems and expanding leaves, stunting overall plant growth and causing the leaves to yellow. Infested alfalfa is more susceptible to cold damage during the winter months.
Adults are long-legged and pear-shaped, between 3-4 millimetres long. Colour varies between light to dark green, and each antennal segment is tipped with a black band. Pea aphid nymphs have a similar appearance but are somewhat smaller.