Scott Hartley, Scott Meers, John Gavloski and prairiepest_admin
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Week 16
Provincial entomologists provide insect pest updates throughout the growing season so we have attempted to link to their most recent information:
● Manitoba’s Insect and Disease Update for 2017 is prepared by John Gavloski and Pratisara Bajracharya and read Issue #13 (posted August 16, 2017) notingsoybean aphids as field near the R6 stage and high levels of bertha armyworm larvae from some fields in western Manitoba.
● Saskatchewan’s Crop Production News – 2017 – Issue #5includes information related to value of late-season disease scouting and record keeping, critical periods for crop water use, and leaving tall-stubble at harvest.
● Watch for Alberta Agriculture and Forestry’s Call of the Land and access the most recent Insect Update (August 17, 2017) provided by Scott Meers. That report notes that diamondback moth are starting to pupate in central and southern fields in the province yet late canola may still need monitoring for DBM larvae, bedstraw hawkmoth larvae (~2.5″ long) have been spotted in canola feeding on volunteer cleavers, the beginning of post-harvest survey for wheat midge and wheat stem sawfly across the province, plus the Agricultural Fieldmen are now ~30% completed the annual grasshopper survey with data coming in already.
West Nile Virus Risk – The regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below. As of August 13 2017, areas highlighted in red on the map below have accumulated sufficient heat for C. tarsalis to fly. Areas highlighted in red, orange and even yellow will have C. tarsalis flying so wear your DEET to stay protected!
The Public Health Agency of Canada posts information related to West Nile Virus in Canada. In 2016, 104 human clinical cases of West Nile Virus were reported. The map of clinical cases of West Nile Virus in Canada in 2017 is updated through the summer and three cases of viral West Nile have been reported so far (as of August 5, 2017). All cases were reported from Ontario (in Timiskaming and Windsor-Essex).
The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance for West Nile Virus in birds. As of August 17, 2017, 1113 birds were examined and 48 have tested positive for West Nile virus; one from Saskatchewan, two from Manitoba, 13 from Ontario, and 32 from Quebec. The Public Health Agency of Canada also monitors and posts updates on the status of WNV in Mosquitoes. As of July 22, 2017, Quebec, Ontario, Manitoba and Saskatchewan have reports of positive mosquito pools of West Nile Virus. A total of 47 positive mosquito pools have been found:
33 from Ontario [Peel Regional (5), Toronto (6), Halton(5), Haliburton-Kwartha-Pine Ridge District(1), Simcoe Muskoka District (1), Windsor-Essex County (6), Eastern Ontario (1), Durham Reginal (1), Hamilton (1), Haliburton-Kawarta-Pine Ridge district (1), Hastings and Prince Edward Countries (2), and York Regional (3)];
11 from Manitoba [(Winnipeg (3), Southern (2), Interlake eastern (1), and Prairie Mountain(5)];
This week’s Insect of the Week is the bronzed blossom pollen beetle. They feed on canola and oilseed rape, mustards, bittercress, rockcress, wild radish and dogmustard. They are not known to be established in Western Canada, but are present in Nova Scotia, PEI and Quebec. Adult females lay clusters of 2 to 3 eggs in developing buds and can lay up to 250 eggs in one summer. Once the eggs hatch, larva enter developing flower buds to feed. This feeding can reduce seed production by up to 70%!
For more information on the bronzed blossom pollen beetle, see our Insect of the Week page.
Weather synopsis – Temperature – This week’s temperatures were warmest in southern Alberta and Manitoba (Fig. 1). The 30-day average temperatures were warmest along the border with USA (Fig. 2).
Figure 1. Average precipitation across the Canadian prairies the past
seven days (August 7-14, 2017).
Figure 2. Average temperature across the Canadian prairies the
past 30 days (July 14-August 14, 2017).
After a fair bit heat across the prairies (Fig. 3), a few of us woke to cooler temperatures (Fig. 4) this week!
Figure 3. Highest temperatures the past seven days (August 10-16, 2017) across
the Canadian prairies.
Figure 4. Lowest temperatures the past seven days (August 10-16, 2017) across
the Canadian prairies.
Precipitation – Seven-day rainfall accumulations were greatest in regions north of the Yellowhead highway (Fig. 5). Total 30-day rainfall accumulations indicate that conditions dryer than normal for most of the prairies, particularly southern and central regions of Alberta (Fig. 6).
Figure 5. Accumulated precipitation the past seven days (August 7-13, 2017).
Figure 6. Percent of average precipitation across the Canadian prairies the past 30 days (July 15-August 13, 2017).
This growing season (April 1 – August 13, 2017), the percent of average precipitation continues to be below average for most of the prairies (Fig. 7).
Figure 7. Percent of average precipitation across the Canadian prairies for the growing season (April 1-August 13, 2017).
The growing degree day map (GDD) (Base 10ºC, March 1 – August 13, 2017) is below:
The growing degree day map (GDD) (Base 5ºC, March 1 – August 13, 2017) is below:
The maps above are all produced by Agriculture and Agri-Food Canada. Growers may wish to bookmark the AAFC Drought Watch Maps for the growing season.
Pre-Harvest Interval (PHI) – Growers with late-season insect pest problems will need to remember to factor in the PHI which is the minimum number of days between a pesticide application and swathing or straight combining of a crop. The PHI recommends sufficient time for a pesticide to break down and a PHI-value is both crop- and pesticide-specific. Adhering to the PHI is important for a number of health-related reasons but also because Canada’s export customers strictly regulate and test for the presence of trace residues of pesticides. An excellent summary of PHI for various pesticides in their various crops was posted by Saskatchewan Agriculture’s Danielle Stephens in 2016 within their Crop Production News.
In 2013, the Canola Council of Canada created and circulated their “Spray to Swath Interval Calculator” which was intended to help canola growers accurately estimate their PHI. Other PHI are described in your provincial crop protection guides and remember that specific crop x pesticide combinations will mean different PHIs. More information about PHI and Maximum Residue Limits (MRL) is available on the Canola Council of Canada’s website.
Diamondback moth (Plutellidae: Plutella xylostella) – Based on Harcourt (1954), this week the DBM model was run with a biofix date of May 21. The following map illustrates that potentially three generations (after the migratory population) may have been completed across most of the prairies.
REMINDER – Once diamondback moth is present in the area, it is important to monitor individual canola fields for larvae. 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. The 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 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.
Across the prairies, provincial staff coordinate diamondback pheromone trapping during the growing season: ● Low numbers of moths have been reported across Saskatchewan for the 2017 pheromone monitoring. ● Manitoba Agriculture and Rural Initiatives posted low DBM counts which can be reviewed here. ● Alberta Agriculture and Forestry has a live 2017 map reporting Diamondback moth pheromone trap interceptions. A copy of the map (retrieved July 20, 2017) is below for reference.
Bertha armyworm (Lepidoptera: Mamestra configurata) – REMINDER – Reporting sites across the prairies have generally reported lower cumulative interceptions and cumulative counts are summarized by provincial staff in Manitoba, SaskatchewanandAlberta.
Scouting tips: ● Some bertha armyworm larvae remain green or pale brown throughout their larval life. ● Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms. ● Young larvae chew irregular holes in leaves, but normally cause little damage. The fifth and sixth instar stages cause the most damage by defoliation and seed pod consumption. Crop losses due to pod feeding will be most severe if there are few leaves. ● Larvae eat the outer green layer of the stems and pods exposing the white tissue. ● At maturity, in late summer or early fall, larvae burrow into the ground and form pupae. Monitoring: – Larval sampling should commence once the adult moths are noted. – Sample at least three locations, a minimum of 50 m apart. – At each location, mark an area of 1 m2 and beat the plants growing within that area to dislodge the larvae. – Count them and compare the average against the values in the economic threshold table below:
Lygus bugs (Lygus spp.) – Reminder – 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. 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. Repeat the sampling in another 14 locations. 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-enhanced or French-enhanced versions are available.
Grasshopper Simulation Model Output – Based on model output, grasshopper development is slightly ahead of long term averages with approximately 80% of the population in the adult stage. The following map presents model data for oviposition. Given the warm conditions across the southern prairies, it is not surprising that oviposition rates are predicted to be greatest in southern Alberta and in south-central Saskatchewan.
Grasshopper scouting steps can be reviewed in the previous Week 13 Post.
The Canola Council of Canada created a guide to help growers estimate swathing time in canola. A screen shot of the downloadable Canola Swathing Guide has been included below for reference.
Wheat surveying – As wheat is harvested, monitoring can begin for two wheat pests including wheat midge and wheat stem sawfly. As soon as the combine passes through, in-field monitoring can commence with: ● Soil core sampling is used to assess the densities of wheat midge cocoons set to overwinter, PLUS ● The number of cut stems can be counted to determine the density of wheat stem sawfly.
By January, forecast and risk maps summarizing surveying efforts for the above pests will be available (e.g., check the Risk Map Page).
More information about these pests 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 or ONLY the Wheat stem sawfly pages. Remember the entire guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.
Cattle dung provides moisture, nutrients, and shelter for numerous insect species and other arthropods. Ralf Jochmann’s video magnificently captures some of this diversity, using close-up photography and narration (https://www.youtube.com/watch?v=-l05EHZMmKE).
Adults of the dung beetle Chilothorax (Aphodius) distinctus are common in cattle dung, particularly in September and early October. Larvae develop in agricultural soils where they can occasionally cause crop damage when present in high densities. For more information on this occasional pest, click here.
