An abbreviated synopsis of the past week is provided below. Recent warm weather across the Canadian prairies helped crop development this past week
The growing degree day map (GDD) (Base 5 ºC, April 1-July 27, 2020) is below (Fig. 1) while the growing degree day map (GDD) (Base 10 ºC, April 1-July 27, 2020) is shown in Figure 2.
The highest temperatures (°C) observed across the Canadian prairies the past seven days ranged from <22 to >34 °C (Fig. 3). So far this growing season (up to July 29, 2020), the number of days above 25 ranges from 0-10 days throughout much of Alberta and into the BC Peace then extends up to 41-50 days in southern Manitoba (Fig. 4).
Cumulative rainfall for the past 7 days was lowest across southern regions of Alberta, Saskatchewan, and Manitoba with the exception of around Regina south to the American border, and southwest Manitoba west into the southeast corner of Saskatchewan (Fig. 5). Cumulative 30-day (Fig. 6) and rainfall for the growing season (April 1-July 29, 2020; Fig. 7) are below.
The maps above are all produced by Agriculture and Agri-Food Canada. Growers can bookmark the AAFC Current Conditions Drought Watch Maps for the growing season. Historical weather data can be access at the AAFC Drought Watch website, Environment Canada’s Historical Data website, or your provincial weather network.
Click to link to last week’s information posted for Wk 13 (released 23Jul2020) to review the predictive model outputs for this insect pest.
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 15 ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (Fig. 1). 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 (Fig. 2), 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 in 2019 (for Wk11). Review that post for descriptions and photos to help with in-field scouting for this economic pest of wheat! Additionally, the differences between midges and parasitoid wasps were featured as the current Insect of the Week in 2019 (for Wk12). 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.
Click to link to last week’s information posted for Wk 13 (released 23Jul2020) to review the predictive model outputs for this insect pest. As larvae now begin to develop and feed in fields, emphasis is now placed on in-field scouting in areas where high moth counts are being intercepted by provincial networks highlighted below.
Weekly Pheromone-baited Trapping Results– Early season detection of bertha armyworm is improved through the use of pheromone-baited unitraps traps deployed in fields across the Canadian prairies. Click each province name to access moth reporting numbers observed in Alberta, Saskatchewan and Manitoba. Remember in-field scouting is required to apply the economic threshold to manage both this pest and its natural enemies. For convenience, screen shots of available maps or data from Alberta, Saskatchewan, and Manitoba are below.
Diamondback moth (Plutellidae: Plutella xylostella) – Once the 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.
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).
On the Canadian prairies, lygus bugs (Heteroptera: Miridae) are normally a complex of several native species usually including Lygus lineolaris, L. keltoni, L. borealis, L. elisus although several more species are distributed throughout Canada. The species of Lygus forming the “complex” can vary by host plant, by region or even seasonally.
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. Adults overwinter in northern climates. 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. 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 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 so sweep in at least 10 locations within a field to estimate the density of lygus bugs. In fact, 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 3).
If the total number is below the lower threshold line (Fig. 3), 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 tables (Tables 1 and 2).
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.
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 Field Heroes campaign continues to raise awareness of the role of beneficial insects in western Canadian crops. Check the recently updated Field Heroes website for scouting guides, downloadable posters, and videos. Learn about these important organisms at work in your fields!
Real Agriculture went live in 2020 with a Pest and Predators podcast series!
The following is offered to predict when Culex tarsalis, the vector for West Nile Virus, will begin to fly across the Canadian prairies (Fig. 1). This week, regions most advanced in degree-day accumulations for Culex tarsalis are shown in the map below (yellow, orange then red highlighted areas). As of July 30, 2020 (Fig. 1), areas highlighted yellow and more imminently orange are approaching sufficient heat accumulation for mosquitoes to emerge. Areas highlighted red NOW HAVE Culex tarsalis flying (Fig. 1) – protect yourself by wearing DEET!
Provincial entomologists provide insect pest updates throughout the growing season so link to their information:
• Manitoba‘s Crop Pest Updates for 2020 are available. Access the July 29, 2020 report. The summary indicates that, “Grasshoppers are the insect of greatest concern to field crops in Manitoba currently. Some populations of diamondback moth above economic threshold have been found in eastern Manitoba recently.”