Released August 9, 2024

Jennifer Otani
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Week 14

Welcome to Week 14 for the 2024 growing season! This week includes:
• Weather synopsis
• Aphids in field crops
• Bertha armyworm
• Diamondback moth
• Lygus bug monitoring
• Grasshopper
• Pre-harvest intervals (PHI)
• Provincial insect pest report links
• Crop report links
• Previous posts

Catch Monday’s Insect of the Week for Week 14 – What’s eating my crop? Cabbage white butterfly

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Questions or problems accessing the contents of this Weekly Update? Please contact us so we can connect you to our information. Past “Weekly Updates” can be accessed on our Weekly Update page.

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Weather synopsis

Jennifer Otani
Categories
Week 14

A full weather summary is not available this week.

Growing degree day (GDD) dynamic maps for the Canadian prairies for Base 5 ºC and Base 10 ºC (April 1-August 5, 2024) can be viewed by clicking the hyperlinks. Over the past 7 days (to August 7, 2024), the lowest temperatures recorded across the Canadian prairies ranged from -4 to 11 °C while the highest temperatures observed ranged from 5 to 35 °C. In terms of precipitation across the Canadian prairies. Review the growing season accumulated precipitation (April 1-August 7, 2024), the growing season percent of average precipitation (April 1-August 7, 2024), and the past 7 days (as of August 7, 2024). Access these maps and more using the AAFC Maps of Historic Agroclimate Conditions interface.

Growers can bookmark the AAFC Maps of Current Agroclimate Conditions for the growing season. Historical weather data can be accessed at the AAFC Drought Watch Historical website, Environment and Climate Change Canada’s Historical Data website, or your provincial weather network. The AAFC Canadian Drought Monitor also provides geospatial maps updated monthly.

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Aphids in field crops

Jennifer Otani, Hugh Philip, Owen Olfert and Meghan Vankosky
Categories
Week 14

Aphid populations can quickly increase at this point in the season and particularly when growing conditions are warm and dry. Access the Provincial Insect Pest Report for Wk14 to remain alert to areas and crops suffering from aphid pest pressure.

Figure 1. Pea aphid adults (each 3-4 mm long) and nymph. Photo: M. Dolinski.

Biological and monitoring information (including tips for scouting and economic thresholds) related to aphids in field crops is posted by:
• Manitoba Agriculture (aphids on cereals, aphids on flax, soybean aphid, aphids on peas)
• Saskatchewan Pulse Growers (aphids in pulse crops or access the PDF copy)
• Saskatchewan Flax Development Commission
• Manitoba Pulse and Soybean Growers (soybean aphids: identification, scouting and management or access the PDF copy)
• The Canola Council of Canada’s “Canola Encyclopedia” section on aphids
• or check your provincial commodity group’s insect pest webpages for more detailed information.

Alternatively, several aphid pest species are described in the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) and is accessible as a free downloadable PDF in either English or French on our Field Guides page. PDF copies of the individual pages have been linked below to access quickly:
• Corn leaf aphid or Rhopalosiphum maidis (Fitch)
• English grain aphid or Sitobion (Macrosiphum) avenae (Fabricius)
• Oat-birdcherry aphid or Rhopalosiphum padi (Linnaeus)
• Pea aphid or Acyrthosiphon pisum (Harris)
• Potato aphid or Macrosiphum euphorbiae (Thomas)
• Soybean aphid or Aphis glycines (Matsumura)
• Turnip aphid or Lipaphis erysimi (Kaltenbach)
• Sugar beet root aphid or Pemphigus betae Doane
• Russian wheat aphid or Diuraphis noxia (Mordvilko)

Over the years, both the Weekly Updates and Insect of the Week have included aphid-related information but also important natural enemy details to support in-field scouting. Review the list below so pest and beneficial insects can be distinguished readily when scouting fields:
• Aphidius wasp (Insect of the Week; 2015 Wk15)
• Aphids in canola (Insect of the Week; 2016 Wk13)
• Aphids in cereals (Insect of the Week; 2017 Wk09)
• Cereal aphid manager APP (Weekly Update; 2021 Wk07) that presently is available only for iOS
• Ladybird larva vs. lacewing larva (Insect of the Week; 2019 Wk18)
• Ladybird beetles and mummies (Weekly Update; 2020 Wk15)
• Lygus bug nymphs vs. aphids (Insect of the Week; 2019 Wk16)
• Hoverflies vs. bees vs. yellow jacket wasps (Insect of the Week; 2019 Wk19)
• Pea aphids: a persistent problem for legume growers (Insect of the Week; 2021 Wk12)
• Soybean aphids and aphid annihilating allies (Insect of the Week; 2022 Wk07)
• Syrphid flies (Insect of the Week; 2015 Wk16)

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Bertha armyworm

Jennifer Otani and Meghan Vankosky
Categories
Week 14

Access the Provincial Insect Pest Report for Wk14 for updates for this economic insect pest.

Remember: in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. Use the images below (Fig. 1) to help identify moths from the by-catch that will be retained in the green phermone-baited unitraps.

Figure 1. Stages of bertha armyworm from egg (A), larva (B), pupa (C), to adult (D). Photos: J. Williams (Agriculture and Agri-Food Canada).

Refer to the PPMN Bertha armyworm monitoring protocol for help when performing in-field scouting or review the 2024 Insect of the Week featuring bertha armyworm. Also scan over the 2019 Insect of the Week featuring bertha armyworm and its doppelganger, the clover cutworm! 

Biological and monitoring information related to bertha armyworm in field crops is posted by the provinces of Manitoba, Saskatchewan, Alberta and the Prairie Pest Monitoring Network. Also, refer to the bertha armyworm pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page.

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Diamondback moth

Jennifer Otani and Meghan Vankosky
Categories
Week 14

Scouting and pest management for diamondback moth depends on in-field counts of larvae per metre2! This means plants need to be pulled and tapped off to assess the number of larvae! Use Figure 1 below to help identify the different stages of the diamondback moth.

Figure 1. The life stages of the diamondback moth (Plutella xylostella), which can have multiple generations per year. Photos: AAFC-Saskatoon-J. Williams.

The economic threshold for immature and flowering canola is 100-150 larvae per metre2.

Access the Provincial Insect Pest Report for Wk14 for updates for this economic insect pest.

Biological and monitoring information for DBM (including tips for scouting and economic thresholds) is posted by Manitoba Agriculture, Saskatchewan Ministry of Agriculture, Alberta Agriculture and Irrigation, and the Prairie Pest Monitoring Network.  Also, refer to the diamondback moth pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our Field Guides page.

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Lygus bug monitoring

Jennifer Otani, Hector Carcamo and Meghan Vankosky
Categories
Week 14

Access the Provincial Insect Pest Report for Wk14 for updates for this economic pest.

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 that focuses feeding activities on developing buds, pods and seeds. Adults overwinter in northern climates. The economic threshold for Lygus in canola is applied at late flower and early pod stages.  

Recent research in Alberta has resulted in a revision to the thresholds recommended for the management of Lygus in canola. Under ideal growing conditions (i.e., ample moisture) a threshold of 20-30 lygus per 10 sweeps is recommended. Under dry conditions, a lower threshold may be used, however, because drought limits yield potential in canola, growers should be cautious if considering the use of foliar-applied insecticide at lygus densities below the established threshold of 20-30 per 10 sweeps. In drought-affected fields that still support near-average yield potential, a lower threshold of ~20 lygus per 10 sweeps may be appropriate for stressed canola. Even if the current value of canola remains high (e.g., >$19.00 per bu), control at densities of <10 lygus per 10 sweeps is not likely to be economical. Research indicates that lygus numbers below 10 per 10 sweeps (one per sweep) can on occasion increase yield in good growing conditions – likely through plant compensation for a small amount of feeding stress.

Figure 1. Adult Lygus lineolaris (5-6 mm long) (photo: AAFC-Saskatoon).
Figure 2. 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. 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 continues 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.

How to tell them apart: The 2019 Insect of the Week’s doppelganger for Wk 15 was lygus bug versus the alfalfa plant bug while Wk 16 featured lygus bug nymphs vs. aphids!  Both posts include tips to discern the difference between when doing in-field scouting!

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 “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our new Field Guides page. The Canola Council of Canada’s “Canola Encyclopedia” also summarizes Lygus bugs. The Flax Council of Canada includes Lygus bugs in their Insect Pest downloadable PDF chapter plus the Saskatchewan Pulse Growers summarize Lygus bugs in faba beans.

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Grasshopper

Jennifer Otani, James Tansey and Meghan Vankosky
Categories
Week 14

Grasshopper Scouting Tips:
● Review grasshopper diversity and photos of nymphs, adults, and non-grasshopper species to aid in-field scouting from egg hatch and onwards.
● It is best to scout on warm days when grasshopper nymphs are more active and easier to observe.
● Carefully check roadside ditches and along field edges but also check the edge of the crop and into the actual field.
● Younger or earlier instar nymphs are easier to manage – visit sites every few days to stay on top of local field conditions.
● A sweep-net can ‘detect’ grasshopper nymphs, however, economic thresholds for grasshoppers are based on the number of grasshoppers per square-metre counts.
● Access the PPMN’s Grasshopper Monitoring Protocol as a guide to help implement in-field monitoring.
● Review grasshopper lifecycle, damage and scouting and economic thresholds to support sound management decisions enabling the preservation of beneficial arthropods and mitigation of economic losses.

Important – A preliminary summary of available thresholds for grasshoppers has been kindly shared by Dr. J. Tansey (Saskatchewan Agriculture) in Table 1. When scouting, compare in-field counts to the available threshold value for the appropriate host crop AND for field or ditch situations. Available thresholds (nominal and economic) help support producers while protecting beneficials (i.e., predators, parasitoids, and pathogens) that regulate natural populations of grasshoppers.

Access the Provincial Insect Pest Report for Wk14 for updates for this economic insect pest.

Biological and monitoring information (including tips for scouting and economic thresholds) related to grasshoppers in field crops is posted by Manitoba Agriculture, Saskatchewan Ministry of Agriculture, Alberta Agriculture and Irrigation, the BC Ministry of Agriculture, and the Prairie Pest Monitoring Network.  Also, refer to the grasshopper pages within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (2018) accessible as a free downloadable PDF in either English or French on our Field Guides page. Review the historical grasshopper maps based on late-summer in-field counts of adults performed across the Canadian prairies.

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Pre-Harvest Intervals (PHI)

Jennifer Otani
Categories
Week 14

As harvest approaches, remember to consider PHI before applying pesticides for late-season pests. The PHI refers to the minimum number of days between a pesticide application and swathing or straight combining of a crop and reflects the time required for pesticides to break down after being applied. PHI values are both crop- and pesticide-specific.  Adhering to the PHI is important for a number of health-related reasons and to ensure that crops being sold for export meet pesticide residue limit requirements.

Helpful resources include:
• The Keep It Clean website, with information about PHI and Maximum Residue Limits (MRL)
• The Pest Management Regulatory Agency fact sheet, “Understanding Preharvest Intervals for Pesticides”, with a free copy available to download
• Keep It Clean’s “Pre-Harvest Interval Calculator” helps to accurately estimate PHI for a variety of crops
• The Pre-Harvest Glyphosate Stage Guide
• The provincial crop protection guides include the PHI for every pesticide by crop combination. The 2023 Crop Protection Guides are available as FREE downloadable PDFs for Alberta, Saskatchewan, and Manitoba for 2024!

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Provincial insect pest report links

Jennifer Otani, John Gavloski, James Tansey, Carter Peru and Shelley Barkley
Categories
Week 14

Prairie-wide provincial entomologists provide insect pest updates throughout the growing season. Follow the hyperlinks to readily access their information as the growing season progresses:

MANITOBA’S Crop Pest Updates for 2024 are available. Access the August 8, 2024 report (or access the PDF copy). Bookmark the insect pest homepage to access fact sheets and more! Highlights reported by Dr. J. Gavloski include:
• Bertha armyworm – Some control of bertha armyworm has occurred in several fields in Southwest Manitoba. Some evidence of diseased bertha armyworms has also been observed. Access Manitoba’s fact sheet for this insect to support in-field scouting for larvae now.
• Lygus bugs – A couple of canola fields in the Eastern region were sprayed for Lygus bugs. Lygus near threshold in sunflowers was reported from the Southwest region.
• European corn borer – A field of corn in the Eastern region was sprayed for European corn borer. Access Manitoba’s fact sheet for this insect.
• Aphids – Aphids are being noticed in some fields of peas (pea aphid), soybeans (soybean aphid), cereal crops (a complex of cereal feeding aphids) and on canola leaves in some area. Currently, in most instances, these are not at economic levels, or the crops are beyond the more susceptible stages. Noticeable levels of predators of aphids, and evidence of parasitism, have also been reported in some areas.
• Thrips – High levels of thrips in barley were reported from the Northwest region.
• Sunflower midge – Some damage from sunflower midge was noticed along the edges of a sunflower field in the Eastern region.
• Insects in Stored Grain – AAFC in Winnipeg is seeking producer participation for grain bin monitoring in September-October 2024. Learn more here and find out how to participate.

SASKATCHEWAN’S Crop Production News is back for the 2024 growing season! Access the online Issue #6 report which notes pea aphids in various pulse and alfalfa crops in southeast Saskatchewan (and includes thresholds to support scouting). The report also notes wheat midge are being caught on traps and a link to their wheat midge webpage. Bookmark their insect pest homepage to access important information! Also access the Crops Blog Posts that released a grasshopper activity update (June 2024), announced registration for the Crop Diagnostic School 2024 but also posts help for scouting fields for wireworms (May 2024), grasshopper identification: pest or not (Apr 2024), a summary of wheat midge populations and management (Mar 2024), and a description of pea leaf weevil populations (Feb 2024). This week in Saskatchewan:
• A brief summary of notable insect pests shared by Dr. J. Tansey is that aphids are the ‘big’ story; aphids in lentils and increasing aphid populations in cereals were noted.
• Localized grasshopper pressure occurred across multiple crops in some parts of Saskatchewan.
• The 2024 Bertha armyworm Pheromone Trap map is now available online (or access a PDF copy of the July 31, 2024 map) and note that counts continue to increase, with a few ‘warm’ spots.

ALBERTA’S Insect Pest Monitoring Network webpage links to insect survey maps, live feed maps, insect trap set-up videos, and more. There is also a Major Crops Insect webpage. Remember, AAI’s Agri-News occasionally includes insect-related information, e.g., diamondback moth and bertha armyworm (August 6, 2024); aphids in field crops, canola flower midge scouting (July 29, 2024); assessing and a description of missing pods on canola (July 22, 2024); scout for wheat midge (July 15, 2024); the right canola crop stage to spray for lygus bugs (July 8, 2024); soil moisture, wheat midge and other insect pests (June 24, 2024); scout for grasshoppers and other insect pests (June 17, 2024); how to manage stem feeding from flea beetles, keep canola bins malathion-free, scout for grasshoppers and other pests (June 10, 2024); scout for insect pests (June 3, 2024); scout for grasshoppers (May 27, 2024); flea beetle control (May 6, 2024); cereal insect pests, latest on insects in canola, and post-emergence wireworm scouting (May 13, 2024).
• Wheat midge monitoring – Cumulative counts arising from weekly data are available so refer to the Live Map. So far, cumulative trap counts from 37 trap locations are reporting; 11 sites in central Alberta are “high” and in the Peace River region 21 sites are reporting “high”, 2 sites are “medium”, and 2 sites are “low” (as of August 1, 2024).
• Cabbage seedpod weevil monitoring – Sweep-net count data can be reported here then the data populates the Live Map. So far, a total of 16 sites in southern Alberta are reporting; there are 14 “low risk” plus 2 “high risk” reports as of August 8, 2024).
• Bertha armyworm pheromone trap monitoring – Cumulative counts arising from weekly data are available so refer to the Live Map. Cumulative trap counts from 272 trap locations are all reporting “low risk” across the province while 1 trap location near Fairview, plus 3 trap locations in southern Alberta (2 in Vulcan County plus 1 near Lethbridge) are reporting “medium risk” as of August 8, 2024). Remember to scout fields for larvae.

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Crop report links

Jennifer Otani
Categories
Week 14

Access the latest provincial crop reports produced by:
• Manitoba Agriculture (subscribe to receive OR access a PDF copy of the August 6, 2024 report).
• Saskatchewan Agriculture (or access a PDF copy of the July 30-August 5, 2024 report).
• Alberta Agriculture and Irrigation (or access a PDF copy of the July 30, 2024 report).

The following crop reports are also available:
• The United States Department of Agriculture (USDA) produces a Crop Progress Report (access a PDF copy of the August 5, 2024 edition).
• The USDA’s Weekly Weather and Crop Bulletin (access a PDF copy of the August 6, 2024 edition).

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Previous posts

Jennifer Otani
Categories
Week 14

As the growing season progresses, the Weekly Update topics move on and off the priority list for in-field scouting. It remains useful to keep the list at hand to support season-long monitoring. Click to review these earlier 2024 Posts (organized alphabetically):
• 2023 Risk maps
• Alfalfa weevil (Wk 09)
• Cabbage seedpod weevil (Wk 10)
• Canola flower midge (Wk 13)
• Cereal leaf beetle (Wk 10)
• Cicada – Rare co-emergence of broods (Wk07)
• Crop production guide links (Wk 03)
• European skipper (Wk 11)
• Cutworms (Wk 05)
• Field heroes (Wk 05)
• Flea beetles (Wk 04)
• Invasive insects (Wk 06)
• Monarch migration (Wk 10)
• Pea leaf weevil (Wk 05)
• Prairie Crop Disease Monitoring Network (Wk 08)
• Prairie Weed Monitoring Network (Wk 06)
• Scouting charts – canola and flax (Wk 03 of 2022)
• Tick tips (Wk 04)
• True armyworm (Wk 09)
• West Nile virus (Wk 09)
• Wind trajectory summaries unavailable (Wk 01)
• Wheat midge (Wk 11)

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