Weekly Update

Jennifer Otani, Owen Olfert, Erl Svendsen and David Giffen
Categories
Week 15

Prairie Pest Monitoring Network Weekly Updates – August 12, 2015


Otani, Giffen, Svendsen, Olfert


  1. Greetings!  An HTML and PDF version of this Weekly Update can be accessed here.  


  1. Weather synopsis – The following weather maps were retrieved from AAFC’s Drought Watch website.  The map below shows the Highest Temperatures the Past 7 Days (July 29-August 10, 2015) across the prairies:

The map below shows the Accumulated Precipitation the past 7 days (i.e., July 29-August 10, 2015):
While the map below reflects the Accumulated Precipitation for the Growing Season (i.e., April 1-August 10, 2015):
The map below reflects the Percent of Normal Precipitation for the Growing Season (i.e., April 1-August 10, 2015) for comparison:
The updated growing degree day (GDD) (Base 5ºC, March 1 – August 9, 2015) map is below:

While the growing degree day (GDD) (Base 10ºC, March 1 – August 9, 2015) map is included below:

  1. Pre-Harvest Interval (PHI) – Growers is late-season insect pest problems will need to remember to factor in the PHI which is 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 and a PHI-value is 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 of canola strictly regulate and test for the presence of trace residues of pesticides.
In 2013, the Canola Council of Canada created and circulated their “Spray to Swath Interval Calculator” which was intended to help canola growers accurately estimate their PHI.  Other PHI are described in your provincial crop protection guides and remember that specific crop x pesticide combinations will mean different PHIs.  A screen shot of the webpage is included below for your reference.
  1. Bertha armyworm (Mamestra configurata) –     In-field monitoring will focus on searching for Bertha armyworm larvae which will feed on leaves but also upon newly developing pods.  Take care to examine the whole plant when scouting.  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:
Sample at least three locations (a minimum of 50 m apart) within a field for larvae.  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).
  1. 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).
  1. Swede midge (Contarinia nasturtii) – Thank you to Dr. Lars Andreassen who provided the following update for swede midge monitoring in Saskatchewan for 2015.  Very low swede midge numbers have been intercepted at pheromone trap monitoring sites across the prairies but these results are not surprising given the drought conditions.  In-field surveying performed by Andreassen et al. (AAFC-Saskatoon) are mapped below for 2015.  Their findings show consistent swede midge populations (larvae and damage symptoms) in northeast Saskatchewan in 2015.  Note there are new records of larvae and swede midge damage at sites surrounding Lloydminster up against the Alberta border in 2015.
Reminder – Swede midge 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 for larvae among the anthers).
  • 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.
  • Young plants that show unusual growth habits should be examined carefully for damage and 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.
  • Refer to the latest Canola Watch for a swede midge update from Dr. Julie Soroka.

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.

  1. 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 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. 

Please find additional detailed information for CSPW in fact sheets posted by Alberta Agriculture and Forestry, Saskatchewan Agriculture, or the Prairie Pest Monitoring Network.

  1. 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 Manitoban, or Albertan fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol.  
Adult Lygus Bug
Adult L. lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Lygus Bug Nymph
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 Bug at Late Flowering Stage
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.
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 early 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).
  1. Time of Swathing – The Canola Council of Canada created a guide to help growers estimate swathing time in canola.  A screen shot of the downloadable guide has been included below for reference.
  1. Harvest Sample Program – The Canadian Grain Commission is ready and willing to grade grain samples harvested in 2015.  This is a FREE opportunity for growers to gain unofficial insight into the quality of their grain and to obtain valuable dockage information and details associated with damage or quality issues.  More information on the Harvest Sample Program is available at the Canadian Grain Commission’s website or growers can register online to receive a kit to submit their grain.  The following screen shot of the CGC webpage offers more details.
  1. Provincial Insect Pest Updates – The following provincial websites have their pest updates posted so click the links to access their reports:
●  Manitoba’s Insect and Disease Report  (August 4, 2015) featuring lygus bugs and a reminder for the Fall grasshopper monitoring plus how it supports the 2016 grasshopper forecast map.
●  Saskatchewan’s Insect Update (July 23, 2015) featuring descriptions of causes of white heads in wheat.
●  Alberta’s Insect Update (Call of the Land audio report of August 6, 2015) featuring lygus bugs, aphids in cereals and diamondback moths.
  1. 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 CanadaThis growing season we will post an “Insect of the Week” in the form of short excerpts from the field guide. This week features the Beet webworm.
  1. Crop Reports –  The following provincial websites now have their Crop Reports posted so click the links to find their weekly updates:
  1. West Nile Virus Risk –  The regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below.  Areas highlighted in red on the map below will have accumulated sufficient heat for C. tarsalis to fly.
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, nine birds in Ontario and five birds in Quebec tested positive for West Nile-related deaths (click here to view the report).
As of August 9, 2015, adult C. tarsalis are predicted to be in flight throughout much of the prairies – apply DEET if you are active outdoors within areas highlighted red, rose or pink in the map below!!  Areas highlighted orange should be prepared with DEET!
  1. Questions or problems accessing the contents of this Weekly Update?  Please e-mail either Dr. Owen Olfert or Jennifer Otani.  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.
  1. Previous topics:
    1. The PPMN Blog is located at http://prairiepestmonitoring.blogspot.ca/    Subscribe to receive the most current information OR bookmark the site to visit later.
    2. 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: EnglishFrench) or ‘Enhanced’ (i.e., best for viewing electronically with active internal and external hyperlinks: English-enhancedFrench-enhanced).
    3. 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.
    4. 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.  
    5. 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 and Forestry).
    6. Pea Leaf Weevil (Sitona lineatus) –Link here for the Pea leaf weevil monitoring protocol which includes photos of related weevils.
    7. Crop Protection Guides – Access Saskatchewan’s Crop Production Guide,  Manitoba’s Guide to Crop Production,  Alberta’s Crop Protection or Blue Book,  or the Western Committee on Crop Pests Guidelines for the Control of Crop Pests.
    8. Canola Insect Scouting Chart – The Canola Insect Scouting Chart has been updated with hyperlinks now directing growers to downloadable pages from the NEW Field Guide!
    9. Alfalfa Weevil (Hypera postica) – Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon).
    10. Cabbage root maggot (Delia spp.) – A summary of root maggot biology, research, and pest management recommendations for canola production was published by Soroka and Dosdall (2011).  Remember there are no registered insecticides for root maggot control in canola.
    11. Wheat midge (Sitodiplosis mosellana) –  – Additional wheat midge biology and monitoring information can be located by clicking here or by linking to provincial fact sheets (Saskatchewan Agriculture or Alberta Agriculture and Forestry).  More information related to wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  
    12. Cereal Leaf Beetles (Oulema melanopus) – Reminder – Fact sheets for Cereal leaf beetle (CLB) are posted by Alberta Agriculture and Forestry, and BC Ministry of Agriculture, and the Prairie Pest Monitoring Network.  
    13. Grasshoppers (Camnulla pellucida, Melanoplus sanguinipes, M. bivittattus, M. packardii) –
Remember only five or six grasshopper species of the 80+ that occur on the prairies are regarded as crop pests.  Economic thresholds for grasshoppers are posted by Manitoba Agriculture, Saskatchewan Agriculture, Alberta Agriculture and Forestry, BC Ministry of Agriculture, and the Prairie Pest Monitoring Network.
    1. Bertha armyworm (Mamestra configurata) – Provincial fact sheets describing the biology and related pest management information for bertha armyworm are posted by Manitoba Agriculture, Food and Rural Development, Saskatchewan Agriculture, Alberta Agriculture and Forestry, or BC Ministry of Agriculture.

Insect of the Week – Beet webworm

Jennifer Otani
Categories
Week 15

This week’s Insect of the Week is the beet webworm (Loxostege sticticalis (Linnaeus)) (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). 

(c) AAFC-AAC

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