Ross Weiss, David Giffen, Serge Trudel, Owen Olfert and Meghan Vankosky
This past week (July 22-28, 2019) temperatures were approximately 2 °C warmer than last week (Fig. 1). The warmest temperatures were observed in MB and southern AB while temperatures were cooler in western AB and the Peace River region.
Across the prairies, 30-day (June 28 – July 28, 2019) average temperatures have been approximately 1 °C cooler than normal (Fig. 2). Temperatures were warmest across MB and eastern SK.
Growing season temperatures (April 1-July 28, 2019; Fig. 3) in AB and SK have been 1 °C cooler than average while central and eastern MB has been approximately 1 °C warmer than average (Fig. 4).
This past week significant rainfall amounts were reported the parkland region of SK and AB (Fig. 5). Across the prairies, rainfall amounts for the past 30 days have been highly variable (Fig. 6).
Dryer conditions continue across southern AB and western SK. Growing season (April 1 – July 21, 2019; Fig. 7) rainfall amounts have been below average across southern regions of AB, and across MB (Fig. 8).
The growing degree day map (GDD) (Base 5 ºC, April 1-July 21, 2019) is below (Fig. 9):
The growing degree day map (GDD) (Base 10 ºC, April 1-July 21, 2019) is below (Fig. 10):
The lowest temperatures (°C) observed the past seven days ranged from at least 12 down to at least 0 °C in the map below (Fig. 11).
The highest temperatures (°C) observed the past seven days ranged from at least 18 up to at least 32 °C in the map below (Fig. 12).
The maps above are all produced by Agriculture and Agri-Food Canada. Growers can bookmark the AAFC Drought Watch Maps for the growing season.
Ross Weiss, David Giffen, Serge Trudel, Owen Olfert and Meghan Vankosky
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).
Based on model runs, approximately 24% of the population should be in the adult stage. Based on climate data, 32% of the population would be expected to be in adult stage. The first map indicates the average instar for grasshopper populations across the prairies (Fig. 1). The second map indicates adult populations are developing across southern MB and SK and a localized area in southern AB (Fig. 2).
Wheat Midge (Sitodiplosis mosellana) – Reminder – Based on fall surveys in 2018, wheat midge populations were expected to be low across most of AB and SK this season. Dry conditions in May and June have resulted in reduced emergence of adult populations across most of SK.
Review last week’s predictive model update (Wk 16) regarding the development for this pest. This week, the percent of adult emergence is depicted across the Canadian prairies as of July 28, 2019 (Fig. 1). 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. Midge emergence is 100% complete in areas highlighted red, 90% complete in areas highlighted orange, and ≤50% in areas highlighted light orange or yellow (Fig. 1).
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.
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.
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 24Jul2019), and Manitoba (locate table on pg 6). regions in all three prairie provinces are reporting “uncertain” risk based on pheromone-baited unitrap cumulative counts.
Refer to the PPMN Bertha armyworm monitoring protocol for help when performing in-field scouting. Use the images below (Fig. 1) to help identify egg masses and the economically important larvae in canola.
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!
The economic threshold for Lygus in canola is applied at late flower and early pod stages.
Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. 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.
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).
Table 2. Economic thresholds for lygus bugs in canola at pod stage (Wise and Lamb 1998).
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.
Whenever possible, monitor and compare pest densities to established economic or action thresholds to protect and preserve pollinators and beneficial arthropods. Economic thresholds, by definition, help growers avoid crop losses related to insect pest species but they rely on in-field scouting!
The following is offered to predict when Culex tarsalis will begin to fly across the Canadian prairies (Fig. 1). 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. As of July 28, 2019, areas highlighted orange are on the verge of approaching sufficient heat accumulation for mosquitoes to emerge. Areas highlighted red in the map below should now have C. tarsalis in flight.
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 2). For example, as of July 28, 2019, Altona MB is predicted to only take 16 days for C. tarsalis to become fully infective!
Provincial entomologists provide insect pest updates throughout the growing season so we link to their most recent information:
• Manitoba‘s Crop Pest Updates for 2019 are posted here. Access Issue #11 posted July 31, 2019, noting continued grasshopper issues, presence of some diamondback larvae and bertha armyworm pheromone trap interception counts that warranting in-field scouting in several regions of that province. There is also a call and link for Manitoban cooperators to perform the annual grasshopper counts. This a vital survey which contributes to the annual grasshopper forecast maps that growers depend upon to help assess risk.
Public summer field events – Coming to a field near you – Prairie field crop entomologists are already scheduled to be at these 2019 field tour events from May-August (be sure to re-confirm dates and details as events are finalized):
August 8, 2019: 2019 Wheatstalk to be held at Teepee Creek AB. View event info/registration details. Entomologists tentatively participating: Jennifer Otani, Shelby Dufton, Amanda Jorgensen, Boyd Mori.
August 8, 2019. Horticulture School. Agriculture and Agri-Food Canada Research Farm, Portage la Prairie, Manitoba. View event info/registration details. Entomologist presenting: John Gavloski, Kyle Bobiwash.
The case of the Monarch butterfly vs. Painted Lady butterfly (also Viceroy butterfly) An orange butterfly fluttered by. Was it a Monarch butterfly (Danaus plexippus)? Or a Painted Lady butterfly (Vanessa cardui)? If it’s a Monarch, it is species of Special Concern listed under the Species at Risk Act and is not a crop pest. Instead, it’s larvae feed solely on milkweed (Asclepias spp.), typically found in wetland areas. Painted Lady larvae, on the other hand, feed on a wider range of plants including sunflower, canola, mustard, borage, soybean, Canada thistle, burdock, knapweed, wormwood and many other plant species. While neither species overwinter in Canada, Monarchs have regular migratory routes into Canada from Mexico through the USA; Painted Ladies are accidental tourists that are on occasion blown up from the US. One important distinguishing characteristic is the distinct black band with white dots that outline the wings of Monarchs. Painted Ladies do not have this band; instead they have thin white markings along the scalloped wing edges.
Viceroy butterflies (Limenitis archippus) are even more difficult to tell from Monarchs. Viceroys are smaller than Monarchs and sport a black line running through the middle (side-to-side) of the hindwing. Like the Monarch, Viceroys are not crop pests as their larvae feed exclusively on trees of the willow family (willow, poplar, cottonwood). For more information about Painted Lady butterflies, see the Insect of the Week page and our posts on the annual Monarch butterfly migration. The case of the innocuous versus the evil twin: When making pest management decisions, be sure that the suspect is actually a pest. This can be challenge since insects often mimic each other or look very similar. An insect that looks, moves and acts like a pest may in fact be a look-alike or doppelganger.
Doppelgangers may be related (e.g. same genus) or may not be related, as in the case of monarch butterflies (Danaus plexippus) and viceroys (Limenitis achrippus). Doppelgangers are usually relatively harmless but sometimes the doppelganger is a pest yet their behaviour, lifecycle or hosts may be different.
Correctly identifying a pest enables selection of the most accurate scouting or monitoring protocol. Identification and monitoring enables the application of economic thresholds. It also enables a producer to select and apply the most effective control option(s) including method and timing of application. For the rest of the growing season, the Insect of the Week will feature insect crop pests and their doppelgangers.