Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
This past week (July 30- August 5, 2019) temperatures were similar to last week (Fig. 1). The warmest temperatures were observed across most of southern SK and eastern AB.
Across the prairies, 30-day (July 6- August 5, 2019) average temperatures (Fig. 2) were similar to long term climate normals (Fig. 3). Temperatures were warmest across MB and eastern SK.
Growing season temperatures (April 1-August 5, 2019) in the Peace River region, central AB and SK have been 1 °C cooler than average while the remainder of the prairies has been warmer than normal (Fig. 4).
Similar to last week, this 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). Dry conditions continue across southern AB and western SK.
Growing season rainfall amounts have been below average across southern regions of AB, and across MB (Fig. 7 and 8).
The growing degree day map (GDD) (Base 5 ºC, April 1-August 5, 2019) is below (Fig. 9):
The growing degree day map (GDD) (Base 10 ºC, April 1-August 5, 2019) is below (Fig. 10):
The lowest temperatures (°C) observed the past seven days ranged from at least 11 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 21 up to at least 34 °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.
Bertha armyworm (Lepidoptera: Mamestra configurata) – Important – Watch for updates from your local provincial monitoring networks who are compiling cumulative pheromone-baited trap interceptions to assess risk levels in Alberta, Saskatchewan (updated 31Jul2019), 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!
Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
Grasshopper Simulation Model Output – Recent, warmer temperatures have resulted in increased grasshopper developmental rates. Surveys in central SK (last week) indicated that grasshopper populations are primarily in the fifth instar and adult stages and in some areas C. pellucida are very abundant. Based on model runs, approximately 50% of the population should be in the adult stage (24% last week). Based on climate data, 60% of the population would be expected to be in adult stage. Model output indicates that oviposition has begun in southern areas prairies.
The first map (Fig. 1) indicates the average instar for grasshopper populations across the prairies with most areas have grasshopper populations that are in the 5th and adult stages. The second map (Fig. 2) indicates adult populations are developing across areas between 49 and 52 degrees North. The last map (Fig. 3) provides an overview of where oviposition is predicted to have started. The yellow and red areas show that oviposition has began across southern MB, southeastern SK and southern AB.
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.
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 August 8, 2019, Winnipeg MB was predicted to only take 16-18 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 #12 posted August 8, 2019, noting continued grasshopper concern, noticeable diamondback moth in some fields and bertha armyworm in an area. There is also a description of the threshold for diamondback moth, larval development, and how to optimally scout for larvae.
Often life choices involve lesser evils. But in the case of lady beetle larva and lacewing larva, they both contribute to the greater good. But which one do you have? Both are voracious aphid, mite, mealy bug, insect egg and other soft bodied insect hunters. In fact, lady beetle larva can consume hundreds of aphids during their development. Lacewing larva are no slouch in that department either. Another name for them is aphidlion and they can consume up to 200 aphids per week.
While both have the same general tapered alligator body, there are few main characteristics that will help to tell them apart.
For more information about these species and more tips on telling them apart, see our Insect of the Week page).
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.