Weekly Update (July 18, 2019; Wk 15) Otani, Weiss, Giffen, Trudel, Svendsen, Olfert, Vankosky

Greetings!

Week 15 and our Staff are out performing surveys, in-field monitoring and are active at various tech-transfer events across the prairies!  Please bookmark the Blog or subscribe to receive the latest growing season information!

Please access the complete Weekly Update either as a series of Posts for Week 15 (July 18, 2019) OR a downloadable PDF. Be sure to check out the Insect of the Week - the rest of the growing season features doppelgangers to aid in-field scouting!

Questions or problems accessing the contents of this Weekly Update?  Please e-mail either Dr. Meghan Vankosky or Jennifer Otani.  Past “Weekly Updates” can be accessed on our Weekly Update page.

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Weather synopsis (July 18, 2019; Wk 15)

Weather synopsis – Prairie temperatures continue to be cooler than average. Though temperatures this week were approximately 2 °C warmer than last week (July 8-14, 2019), the seven-day average temperature was 0.5 °C cooler than normal (Fig. 1).  The warmest temperatures were observed across MB while temperatures were cooler in western SK and across AB. 

Figure 1. Average temperature (°C) across the Canadian prairies the past seven days (July 8-14, 2019).

Across the prairies, 30-day (June 14 – July 14, 2019) average temperatures have been approximately 1 °C cooler than normal (Fig. 2). Average 30-day temperatures were 0 to 2 °C warmer than average across MB and 0 to 2 °C cooler than average in SK and AB. Growing season temperatures (April 1-July 14, 2019) have been 1 °C cooler than average; the warmest temperatures were observed across the southern prairies (Fig. 3). 

Figure 2. Average temperature (°C) across the Canadian prairies the past 30 days (June 14-July 14, 2019).

Figure 3. Average temperature (°C) across the Canadian prairies for the growing season (April 1-July 14, 2019).

Figure 4. Mean temperature difference from Normal (°C) observed across the Canadian prairies the past 30 days (June 18-July 15, 2019).  Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (18Jul2019).  Access the full map at http://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true

This past week significant rainfall amounts were reported MB and southeastern SK while minimal rainfall was reported across southwestern SK and southern AB (Fig. 5). 

Figure 5. Cumulative precipitation observed the past seven days across the Canadian prairies (July 8-14, 2019).

Across the prairies, rainfall amounts for the past 30 days have been highly variable (Fig. 6). Dry conditions continue across much of southern AB. Rainfall was well above average in SK.  

Figure 6. Cumulative precipitation observed the past seven days across the Canadian prairies (June 15-July 15, 2019).

Growing season (April 1 – July 14, 2019) rainfall amounts have been below average across southern regions of AB, central SK, and central MB (Fig. 7). 

Figure 6. Cumulative precipitation observed over the growing season (April 1-July 15, 2019) across the Canadian prairies.

Figure 7. Percent of average precipitation observed across the Canadian prairies for the growing season (April 1-July 17, 2019).  Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (18Jul2019).  Access the full map at http://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true

Based on modeled soil moisture (Fig. 8), recent rains have improved soil moisture values across a large area of SK and MB. Predicted soil moisture continues to be low across large regions of southern and central areas of AB and western SK. 

Figure 8.  Modeled soil moisture (%) across the prairies (up to July 15, 2019).

The growing degree day map (GDD) (Base 5 ºC, April 1-July 14, 2019) is below (Fig. 9):

Figure 9. Growing degree day (Base 5 ºC) across the Canadian prairies for the growing season (April 1-July 14, 2019).

The growing degree day map (GDD) (Base 10 ºC, April 1-July 14, 2019) is below (Fig. 10):

Figure 10. Growing degree day (Base 10 ºC) across the Canadian prairies for the growing season (April 1-July 14, 2019).

The lowest temperatures (°C) observed the past seven days ranged from at least 14 down to at least 2 °C in the map below (Fig. 11).

Figure 11. Lowest temperatures (°C) observed across the Canadian prairies the past seven days (to July 17, 2019).

Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (18Jul2019).  Access the full map at http://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true

The highest temperatures (°C) observed the past seven days ranged from less than 16 up to at least 30 °C in the map below (Fig. 12).

Figure 12. Highest temperatures (°C) observed across the Canadian prairies the past seven days (to July 17, 2019).

Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (18Jul2019).  Access the full map at http://www.agr.gc.ca/DW-GS/current-actuelles.jspx?lang=eng&jsEnabled=true

The maps above are all produced by Agriculture and Agri-Food Canada.  Growers can bookmark the AAFC Drought Watch Maps for the growing season.

Wheat midge (July 18, 2019; Wk 15)

Wheat Midge (Sitodiplosis mosellana) – Where wheat midge are present, cool, dry conditions in May and June have resulted in delayed emergence of adults. Wheat midge larvae have moved to the soil surface and pupae are appearing.  In some locations adults should be beginning to emerge. The wheat midge model predicts that 44% (45% last week) of the population are in the larval  cocoon stage and 37% (47% last week) of the population is predicted to have moved to the soil surface. This week 12% (7% last week) is predicted to be in the pupal stage. Adults continue to emerge in localized areas in localized areas across all three provinces. 

The first map (Fig. 1) indicates the percent of the population that is in the pupal stage.  The second map (Fig. 2) indicates that less than 10% of the adult population has emerged.  The last map (Fig. 3) indicates that oviposition may be occurring in localized areas. It should be noted that, based on fall surveys in 2018, wheat midge populations were expected to be low across most of AB and SK.

Figure 1.  Predicted percent of wheat midge (Sitodiplosis mosellana) populations at PUPAL STAGE across the Canadian prairies (as of July 15, 2019).

Figure 2. Predicted percent of wheat midge (Sitodiplosis mosellana) populations at ADULT STAGE across the Canadian prairies (as of July 15, 2019).

Figure 3. Predicted percent of wheat midge (Sitodiplosis mosellana) populations where egg laying has begun across the Canadian prairies (as of July 15, 2019).

Monitoring:
When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis.  

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 (photographed by AAFC-Beav-S. Dufton & A. Jorgensen below). 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.

REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision.  Also remember that the parasitoid, Macroglenes penetrans (photographed by AAFC-Beav-S. Dufton 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.

Economic Thresholds for Wheat Midge:
a) To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.
b) 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. 

Wheat midge and its doppelganger, the lauxanid fly, were featured as the Insect of the Week (for Wk10).  Check that post for help with in-field scouting for this economic pest of wheat!  The differences between midges and parasitoid wasps are featured as the current Insect of the Week (for Wk11).  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.

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry).  A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  

Alberta Agriculture and Forestry has a YouTube video describing in-field monitoring for wheat midge.  

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.

Predicted grasshopper development (July 18, 2019; Wk 15)

Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper).

Cool temperatures continue to result in reduced grasshopper developmental rates. Based on model runs, approximately 7% (12.5% last week) of the population is in the first instar, 12% (23% last week) is predicted to be in the second instar, and 27% (32% last week)  is in the third instar, 30% (21% last week) are predicted to be in the fourth instar and 18% (4% last week) are predicted to be in the fifth instar.  As of July 14, 1% of melanopline species are predicted to be in the adult stage. 

The following map (Fig. 1) indicates that grasshopper populations across the southern prairie are mostly in the third and fourth instars. Grasshopper development has been greatest near Winnipeg MB.

Figure 1. Predicted development stages of grasshopper (Melanoplus sanguinipes) populations across

the Canadian prairies (as of July 15, 2019). 

Last week, the Insect of the Week's Doppelganger featured GRASSHOPPERS!!!  Check out the excellent nymph photos to help your in-field scouting!

Biological and monitoring information related to grasshoppers in field crops is posted by Manitoba Agriculture, Saskatchewan Agriculture, Alberta Agriculture and Forestry, 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" which is available as a free downloadable document in either an English-enhanced or French-enhanced version.

Bertha armyworm monitoring (July 18, 2019; Wk 15)

Bertha armyworm (Lepidoptera: Mamestra configurata) - Predictive model updates are completed for the growing season but can be reviewed here (Wk 14).  

Important - Watch for updates from your provincial monitoring networks who are compiling cumulative pheromone-baited trap interceptions to assess risk levels in Alberta, Saskatchewan (updated 10Jul2019), and Manitoba (look on pg 7).

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" which is a free downloadable document as both an English-enhanced or French-enhanced version.

Refer to the PPMN Bertha armyworm monitoring protocol for help when performing in-field scouting.  Use the images below (Fig. 3) to help identify egg masses and the economically important larvae in canola.

Figure 3. Stages of bertha armyworm from egg (A), larva (B), pupa (C) to adult (D).
Photos: J. Williams (Agriculture and Agri-Food Canada)

Now is the time to do in-field scouting for this insect pest.  Review the Insect of the Week which features bertha armyworm and its doppelganger, the clover cutworm!

Lygus in canola (July 18, 2019; Wk 15)

Lygus bugs (Lygus spp.) - The Insect of the Week's doppelganger is the lygus bug versus the alfalfa plant bug. It includes tips to to discern the difference between these plant bug complexes when doing in-field scouting!

The economic threshold for Lygus in canola is applied at late flower and early pod stages.  

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.

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.  For lygus bug monitoring, 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 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).

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.

Cabbage seedpod weevil (Jul 18, 2018; Wk 15)

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.

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.

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 in-field CSPW scouting data then check the online map posted by Alberta Agriculture and Forestry (screenshot retrieved 18Jul2019 provided below as reference).

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

Diamondback moth (July 18, 2019; Wk15)

Diamondback moth (Plutellidae: Plutella xylostella) - Once diamondback moth is present in the area, it is important to monitor individual canola fields for larvae.  Warm growing conditions can quickly translate into multiple generations in a very short period!

Monitoring:

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 (Fig. 1) dislodged from the plant. Repeat this procedure at least in five locations in the field to get an accurate count.

Figure 1. Diamondback larva measuring ~8mm long.
Note brown head capsule and forked appearance of prolegs on posterior.

Figure 2. Diamondback moth pupa within silken cocoon.

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).

Figure 3. Diamondback moth.

Biological and monitoring information for DBM is posted by Manitoba Agriculture, Saskatchewan Agriculture, and the Prairie Pest Monitoring Network.  

More information about Diamondback moths can be found by accessing the pages from the  "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide".  View ONLY the Diamondback moth page but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.

West Nile Virus and Culex tarsalis (July 18, 2019; Wk 15)

West Nile Virus Risk –  Reminder - In 2018, there were 426 human clinical cases of West Nile virus (WNV) in Canada (Fig. 1). 

Figure 1. Geographic distribution of WNV human clinical cases and asymptomatic infections in Canada, 2018.
Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (11Jul2019).  Access the full map at https://www.canada.ca/en/public-health/services/publications/diseases-conditions/west-nile-virus-surveillance/2018/november-11-december-15-week-46-50.html

Health Canada posts information related to West Nile Virus in Canada.  Health Canada also tracks WNV through human, mosquito, bird and horse surveillance.  Link here to access the most current weekly update (July 6, 2019). The screenshot below was retrieved 18Jul2019 as reference but access that information here.

The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance for West Nile Virus in birds.  Take note of the provincial distribution of positive WNV birds in 2018 (table posted below as reference).

The following is offered to predict when Culex tarsalis will begin to fly across the Canadian prairies (Fig. 2). Protect yourself by wearing DEET!  This week, regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below.  Areas highlighted yellow in the map below (Fig. 2) are on the verge of approaching sufficient heat accumulation for mosquitoes to emerge.  Areas highlighted lime green should be preparing for C. tarsalis flight.

Figure 2. Predicted development of Culex tarsalis, across the Canadian prairies (as of July 14, 2019).

Once adults emerge, the following map demonstrates how quickly a Culex tarsalis mosquito carrying WNV can become fully infective (i.e., when it has accumulated 109 base 14.3° degree days) - it's a matter of days, depending on the region (Figure 3).