Saskatchewan Agriculture just posted their 2015 Bertha Armyworm Map. The relative risk appears to be low based on cumulative pheromone trap counts to date but scroll down the webpage to access a PDF copy of the map.
Jennifer Otani, Erl Svendsen, David Giffen and Owen Olfert
Categories
Week 11
Prairie Pest Monitoring Network Weekly Updates – July 15, 2015
Otani, Giffen, Svendsen, Olfert
Greetings! This week grasshoppers, cabbage seedpod weevil and wheat midge were important pests based on provincial reports and reminders for in-field scouting. Rain fell in some areas of the prairies but many continue to wait for moisture. Remember, a downloadable version of this Weekly Update can beaccessed here.
Weather synopsis – Thanks to the folks who compile and manage the agroclimate maps posted by AAFC! The map below shows the Accumulated Precipitation the past 7 days (i.e., July 7-13, 2015):
While the map below reflects the Accumulated Precipitation for the Growing Season (i.e., April 1-July 13, 2015):
The map below reflects the Percent of Normal Precipitation for the Growing Season (i.e., April 1-July 13, 2015) for comparison:
The map below shows the Lowest Temperatures the Past 7 Days (July 7-13, 2015) across the prairies:
While the map below shows the Highest Temperatures the Past 7 Days (July 7-13, 2015) across the prairies:
The updated growing degree day (GDD) (Base 5ºC, March 1 – July 12, 2015) map is below:
While the growing degree day (GDD) (Base 10ºC, March 1 – July 12, 2015) map is included below:
Bertha armyworm (Mamestra configurata) –Low cumulative counts of BAW moths were again reported in pheromone traps throughout the prairies this week.
Growers in Alberta can refer to the live 2015 Bertha armyworm map which is posted by Alberta Agriculture and Forestry that reflects cumulative counts of moths intercepted.
Growers in Manitoba can refer to the latest Insect and Disease Report (updated July 10, 2015) for BAW cumulative count updates.
In-field monitoring for egg masses (Refer to photo below) and newly emerged larvae (photo below) should initially focus on the undersides of leaves plus watch the margins of leaves for feeding. Bertha armyworm larvae will also feed on newly developing pods so the whole plant should be examined. Watch for the following life stages:
Reminder: Some bertha armyworm larvae remain green or pale brown throughout their larval life. Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms. Young larvae chew irregular holes in leaves, but normally cause little damage. The fifth and sixth instars cause the most damage by defoliation and seed pod consumption. Crop losses due to pod feeding will be most severe if there are few leaves. Larvae eat the outer green layer of the stems and pods exposing the white tissue. At maturity, in late summer or early fall, larvae burrow into the ground and form pupae.
Monitoring:
Larval sampling should commence once the adult moths are noted. Sample at least three locations, a minimum of 50 m apart. At each location, mark an area of 1 m2 and beat the plants growing within that area to dislodge the larvae. Count them and compare the average against the values in the economic threshold table below:
Table 1. Economic thresholds for Bertha armyworm in canola (courtesy Manitoba Agriculture, Food and Rural Initiatives).
Expected Seed Value – $ / bushel*
Spraying cost –
$ / acre
6
7
8
9
10
11
12
13
14
15
16
Number of Larvae / metre2 *
7
20
17
15
13
12
11
10
9
9
8
8
8
23
20
17
15
14
13
11
11
10
9
9
9
26
22
19
17
16
14
13
12
11
10
10
10
29
25
22
19
17
16
14
13
12
11
11
11
32
27
24
21
19
17
16
15
14
13
12
12
34
30
26
23
21
19
17
16
15
14
13
13
37
32
28
25
22
20
19
17
16
15
14
14
40
35
31
27
24
22
20
19
17
16
15
15
43
37
32
29
26
23
22
20
19
17
16
* Economic thresholds for bertha armyworm are based on an assumed yield loss of 0.058 bu/acre for each larva/metre2 (Bracken and Bucher. 1977. Journal of Economic Entomology. 70: 701-705).
Grasshoppers (Camnulla pellucida, Melanoplus sanguinipes, M. bivittattus, M. packardii) – In-field scouting along field margins and in ditches AND within the field is critical now with the exceedingly dry growing conditions!
Scouting – Remember only five or six grasshopper species of the 80+ that occur on the prairies are regarded as crop pests. The lifecycles of these six economically important species are similar. Nymphs hatch from overwintered eggs in the spring. Nymphs develop through five stages or instars before becoming adults. Typically, the most serious economic damage will occur from the third to fifth instar stages but all stages need to be monitored. The life stages of the clearwinged grasshopper (Camnulla pellucida) are shown below. Note that adults possess fully formed wings that extend the entire length of the abdomen.
Life stages of the clearwinged grasshopper include (left to right) eggs which overwinter, first instar nymphs that hatch in the spring followed by second, third, fourth and fifth instar nymphs which finally develop into the adult stage.
Need help distinguishing grasshopper nymph stages? Saskatchewan Agriculture’s latest Insect Update includes line drawings to help! It also includes a summary of economic thresholds for grasshoppers in various crops.
Diamondback Moth (Plutella xylostella) – In-field monitoring for DBM larvae should continue this week.
Larval Monitoring:
Once the diamondback moth is present in the area, it is important to monitor individual canola fields for larvae. Remove the plants in an area measuring 0.1 m2 (about 12″ square), beat them on to a clean surface and count the number of larvae dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.
Remember, parasitoid wasps attacking DBM larvae (Refer to photo below) are already present in fields. Use the economic thresholds to preserve these beneficial wasps by NOT applying insecticide until DBM larval densities exceed the threshold.
Diamondback larva (upper left) and pupal silk cocoon (upper right), Diadegma insulare adult and early instar Diamondback moth larvae on canola leaf (lower left) and D. insulare pupae (N=2) within Diamondback moth pupal silk cocoons (lower right).
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).
Wheat Midge (Sitodiplosis mosellana) – This season, predictive modelling was used in an attempt to forecast wheat midge emergence. In 2014, the degree-day model proposed by German researchers (Basedow) was used to predict adult midge emergence in the Peace River region compared to the 5°C base temperature model which corresponds well to midge emergence throughout central and southern areas of the prairies. The map below predicts the geographic distribution and corresponding accumulation of heat units necessary for wheat midge to emerge from puparia developing in the soil.
The map below indicates the predicted status of wheat midge emergence with 10% of resident midge population emerged in areas highlighted yellow (600-693 DD), 50% in areas highlighted gold (693-784 DD), and 90% of resident midge emerged in areas highlighted orange (784-874 DD) using current weather data (up to July 12, 2015). Wheat midge emergence is predicted to be 100% completed (as of July 12, 2015) with the initial midge larvae now expected to be found within wheat heads growing in southern Alberta, southeast Saskatchewan, southwest Manitoba and to the south of Winnipeg. Wheat midge emergence is predicted to be 90% completed (as of July 12, 2015) throughout most of the boreal region of the prairies and in the north Peace. Wheat midge emergence is predicted to be 50% completed (as of July 12, 2015) throughout the remaining portions of the prairies.
When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis. Additional wheat midge biology and monitoring information can be located by clicking here or linking to your provincial fact sheet (Saskatchewan Agricultureor Alberta Agriculture and Forestry). More information related to wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.
REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (shown below), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember your insecticide control options for wheat midge also kill these beneficial insects which help reduce midge populations.
In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads. Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.
Economic Thresholds for Wheat Midge:
To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.
For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled.
Inspect the developing kernels for the presence of larvae and the larval damage.
Adult: Adult cereal leaf beetles (CLB) have shiny bluish-black wing-covers (Refer to figure below). The thorax and legs are light orange-brown. Females (4.9 to 5.5 mm) are slightly larger than the males (4.4 to 5 mm). Adult beetles overwinter in and along the margins of grain fields in protected places such as in straw stubble, under crop and leaf litter, and in the crevices of tree bark. They favour sites adjacent to shelterbelts, deciduous and conifer forests. They emerge in the spring once temperature reaches 10-5ºC and are active for about 6 weeks. They usually begin feeding on grasses, then move into winter cereals and later into spring cereals.
Egg: Eggs are laid approximately 14 days following the emergence of the adults. Eggs are laid singly or in pairs along the mid vein on the upper side of the leaf and are cylindrical, measuring 0.9 mm by 0.4 mm, and yellowish in colour. Eggs darken to black just before hatching.
Larva: The larvae hatch in about 5 days and feed for about 3 weeks, passing through 4 growth stages (instars). The head and legs are brownish-black; the body is yellowish. Larvae are usually covered with a secretion of mucus and fecal material, giving them a shiny black, wet appearance (Refer to figure below). When the larva completes its growth, it drops to the ground and pupates in the soil.
Pupa: Pupal colour varies from a bright yellow when it is first formed, to the colour of the adult just before emergence. The pupal stage lasts 2 – 3 weeks. Adult beetles emerge and feed for a couple of weeks before seeking overwintering sites. There is one generation per year.
Cereal leaf beetle adult (left) and larva (right).
Leaf damage resulting from feeding by cereal leaf beetle larvae.
Monitoring:
Give priority to following factors when selecting monitoring sites:
□ Choose fields and sections of the fields with past or present damage symptoms.
□ Choose fields that are well irrigated (leaves are dark green in color), including young, lush crops. Areas of a field under stress and not as lush (yellow) are less likely to support CLB.
□ Monitor fields located along riparian corridors, roads and railroads.
□ Survey field areas situated near brush cover or weeds, easy to access, or are nearby sheltered areas such as hedge rows, forest edges, fence lines, etc.
Focus your site selection on the following host plant priorities:
● First – winter wheat. If no winter wheat is present then;
● Second – other cereal crops (barley, wheat, oats, and rye). If no cereal crops are present then;
● Third – hay crops. If no hay crops or cereal crops are present then;
● Fourth – ditches and water corridors
Sweep-net Sampling for Adults and Larvae:
A sweep is defined as a one pass (from left to right, executing a full 180 degrees) through the upper foliage of the crop using a 37.5 cm diameter sweep-net. A sample is defined as 100 sweeps taken at a moderate walking pace collected 4-5 meters inside the border of a field. At each site, four samples should be collected, totaling 400 sweeps per site. The contents of each sample should be visually inspected for life stages of CLB and all suspect specimens should be retained for identification. Please note that, because the CLB larvae are covered in a sticky secretion, when they are caught in a sweep-net they are often covered in debris and are very difficult to see. To help determine the presence of CLB, place the contents of the sweep net into a large plastic bag for observation.
Visual Inspection:
Both the adults and larvae severely damage plants by chewing out long strips of tissue between the veins of leaves, leaving only a thin membrane. When damage is extensive, leaves turn whitish (Figure 14). The plant may be killed or the crop may be seriously reduced. In addition to feeding damage, inspectors should be looking for all life stages of the CLB. In a field of host material the visual survey should be conducted between “sweep samples”. Other locations to be examined include grass covered ditch banks and young host crops that are too low to sweep. Experienced surveyors should spend 15 minutes on visual inspection. Less experience surveyors should spend an additional 10 minutes on the visual component.
Swede midge (Contarinia nasturtii) – Reminder – This season we again include scouting tips for in-field monitoring:
□ Watch for unusual plant structures and plant discolourations then follow-up by closely scrutinizing the plant for larvae (Refer to Figure below).
□ The growing tip may become distorted and produce several growing tips or none at all, young leaves may become swollen, crinkled or crumpled and brown scarring caused by larval feeding may be seen on the leaf petioles and stems.
□ Flowers may fail to open.
□ Youngplants that show unusual growth habits should be examined carefully for damageand larvae, especially if the sticky liners have many flies resembling midges (swede midges are about the size of orange blossom wheat midge but are not orange).
□ Larvae can be seen with a hand lens.
In 2014, Canola School posted a swede midge update entitled “ Swede midge a pest on the rise”, featuring Dr. Julie Soroka (AAFC-Saskatoon). The Ontario Canola Growers post swede midge information here. Dr. Rebecca Hallett has posted a very helpful swede midge identification guide for those performing in-field monitoring and pheromone trapping. Finally, canola management recommendations for swede midge in Ontario are posted by Rebecca Hallett and Brian Hall.
Cabbage seedpod weevil (Ceutorhynchus obstrictus) – There is one generation of CSPW per year and the overwintering stage is the adult which is an ash-grey weevil measuring 3-4mm long (Refer to lower left photo). Adults typically overwinter in soil beneath leaf litter within shelter belts and roadside ditches. They emerge from overwintering in the spring as soil temperatures warm to ~15°C. CSPW utilize several flowering hosts including wild mustard, flixweed, hoary cress, stinkweed and volunteer canola. CSPW move to canola during the bud to early flower stages and will feed on pollen and buds, causing flowers to die. 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.
Monitoring: 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 dayto 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.
Cabbage root maggot (Delia spp.) – Among root feeding pests of canola, historically five species of Delia flies have been identified across the Canadian prairies; Delia radicum (L.), D. floralis (Fallén), D. platura (Meigan), D. planipalpis (Stein), and D. florilega (Zett.) have been observed in canola over 30 years of research (Liu and Butts 1982, Griffiths 1986a, Broatch and Vernon 1997; Soroka and Dosdall 2011). A summary of root maggot biology, research, and pest management recommendations for canola production was published by Soroka and Dosdall (2011).
Root maggots continue to be a problematic in canola production largely owing to the fact that (i) the species is composition varies by geographic latitude and local conditions, plus (ii) one or two generations per year will occur but varies by species. The species complex is typically characterized by multiple, overlapping generations of Delia resulting in adults laying eggs in canola (Refer to upper left photo for adult and eggs) from late Spring to October and maggots feeding on roots from late rosette until late fall (Refer to upper right photo). Root maggots pupate and overwinter within cigar-shaped, reddish-brown puparia 5-20 cm below the soil surface (Soroka and Dosdall 2011) so canola-on-canola rotations should be avoided. In the spring, adults emerge from mid-May to mate and females lay oval, white eggs singly or in batches near the base of cruciferous host plants over a 5-6 week period. The larvae develop through three instar stages which feed on root hairs then secondary roots initially whereas older maggots will feed into the taproot of a canola plant.
Remember there is no registered insecticide for root maggot control in canola.
Lygus bugs (Lygus spp.) – The economic threshold for Lygus in canola is applied at late flower and early pod stages. Biological and monitoring information can be linked by clicking here or you can access the Manitoba, or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol.
Adult L. lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).
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. They 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.
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.
Repeat the sampling in another 14 locations. 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 C). If the total number is below the lower threshold line, 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 table.
Sequential sampling for lygus bugs at late flowering stage in canola.
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.
Table 1. Economic thresholds for lygus bugs in canola at late flowering and early pod stages (Wise and Lamb 1998).
1 Canola crop stage estimated using Harper and Berkenkamp 1975).
2 Economic thresholds are based on an assumed loss of 0.1235 bu/ac per lygus bug caught in 10 sweeps (Wise and Lamb. 1998. The Canadian Entomologist. 130: 825-836).
Table 2. Economic thresholds for lygus bugs in canola at pod stage (Wise and Lamb 1998).
3 Economic thresholds are based on an assumed loss of 0.0882 bu/ac per lygus bug caught in 10 sweeps (Wise and Lamb. 1998. The Canadian Entomologist. 130: 825-836).
Provincial Insect Pest Updates – The following provincial websites have their pest updates posted so click the links to access their reports:
● Alberta’s Insect Update (Call of the Land audio report of July 16, 2015)
Insect of the Week – Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide (2015) by Hugh Philip is a new publication from Agriculture and Agri-Food Canada. This growing season we will post an “Insect of the Week” in the form of short excerpts from the field guide. This week features several species of aphids (i.e., corn leaf, English grain, green peach, oat-birdcherry, pea, potato, soybean, turnip, greenbug).
Additionally, ladybird beetles were also featured in the Insect of the Week.
Crop Reports – The following provincial websites now have their Crop Reports posted so click the links to find their weekly updates:
West Nile Virus Risk – Reminder – Now is the time for DEET!The regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below. Areas yet to be highlighted in red on the map below will have accumulated sufficient heat for C. tarsalis to fly. As of July 12, 2015, the predicted development of C. tarsalis is most advanced in the southern areas of our prairie provinces with adults predicted to emerge from 350-400 DD in the map below ( will be highlighted in red).
The Public Health Agency of Canada posts information related to West Nile Virus in Canada and their website is located here. The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance. As of this week, one bird in New Brunswick and one bird in Ontario tested positive for West Nile-related deaths (click here to view the report).
Questions or problems accessing the contents of this Weekly Update? Please e-mail or call either Owen.Olfert@agr.gc.ca (tel. 306-385-9355) or Jennifer.Otani@agr.gc.ca (tel. 780-354-5132). Past and present “Weekly Updates” are very kindly posted to the Western Forum website by webmaster, Dr. Kelly Turkington. Please click here to link to that webpage.
Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide – The NEW Field Guide to Support Integrated Pest Management (IPM) in Field and Forage Crops is NOW available for download from www.publications.gc.ca. Two downloadable (~8 MB) versions of the complete field guide are available as either a ‘Regular’ (i.e., best for printing: English, French) or ‘Enhanced’ (i.e., best for viewing electronically with active internal and external hyperlinks: English-enhanced, French-enhanced).
Wind trajectories Related to Diamondback Moth (DBM) and Aster Leafhopper Introductions – Completed for the season. Please refer to earlier Weekly Updates for details related to backward and forward trajectories associated with air parcels moving over western Canadian locations.
Flea Beetles (Chrysomelidae: Phyllotreta species) – Helpful images produced by Dr. Julie Soroka (AAFC-Saskatoon) exemplifying percent of cotyledon leaf area consumed by flea beetles are posted at Canola Watch.
Cutworms (Noctuidae) – Cutworm biology, species information, plus monitoring recommendations are available at the Prairie Pest Monitoring Network’s Cutworm Monitoring Protocol. Also refer to these cutworm-specific fact sheets (Manitoba Agriculture and Rural Initiatives, Alberta Agriculture, Food and Rural Development). If cutworms are spotted in Albertan fields, please also consider using the Alberta Pest Surveillance Network’s “2015 Cutworm Reporting Tool” for online reporting located by clicking here. Data entered at that website uploads to a live “Cutworm Map”.
Canola Insect Scouting Chart – Reminder – The Canola Insect Scouting Chart has been updated with hyperlinks now directing growers to downloadable pages from the NEW Field Guide!
Alfalfa Weevil (Hypera postica) – Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon).
This week’s Insect of the Week is a two-fer: aphids and their natural mortal enemies, ladybird beetles (from the new Field Crop and Forage Pests and their Natural Enemies in Western Canada – Identification and Management Field Guide – download links available on the Insect of the Week page).
