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 July 13, 2017, areas highlighted in yellow on the map below have accumulated sufficient heat for the initial C. tarsalis to begin to fly whereas areas highlighted in orange have to C. tarsalis flying so wear your DEET to stay protected!
The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance for West Nile Virus in birds. As of July 20, 2017, 833 birds were examined and eight have tested positive for West Nile virus; four from Ontario, one from Saskatchewan, and one from Quebec.
This week’s Insect of the Week is Tetrastichus julis. They are a parasitoid enemy of the cereal leaf beetle. Mature larvae overwinter in infested cereal leaf beetle cocoons and emerge in spring to lay more eggs in cereal leaf beetle larvae. Adults feed on nectar and aphid honeydew.
Ross Weiss, David Giffen, Owen Olfert and prairiepest_admin
Weather synopsis – Seven-day rainfall accumulations were generally greater than the previous week. Some areas in southern prairies received 10 to 30 mm of rain (Fig. 1). Total 30-day rainfall for June 17 to July 16, 2017, indicates that conditions are somewhat dryer than normal for most of the prairies. Figure 2 indicates that the regions with <40% of average rainfall (30-day) now include much of southern Saskatchewan, as well as large spots of southern Alberta and Manitoba. The percent of average precipitation for this growing season continues to be average for most of Alberta and below average for much of Saskatchewan and Manitoba (Fig. 3).
Figure 1. Accumulated precipitation across the Canadian prairies the past seven days (July 10-16, 2017).
Figure 2. Accumulated precipitation across the Canadian prairies the past 30 days (June 17-July 16, 2017).
Figure 3. Percent of average precipitation across the Canadian prairies from June 17-July 16, 2017.
Over the past week, the warmest temperatures occurred over a large area from Brandon to Edmonton and south to the Canada-USA border. Although temperatures were warmer (1°C) than last week, both the 7- and 30-day average temperatures were similar to long-term normal (LTN). Compared to 30-day average temperatures, Alberta was above normal whereas Saskatchewan and Manitoba were slightly below normal.
The lowest temperatures across the prairies over the past seven days (July 13-19, 2017) are mapped below.
In contrast, the highest temperatures recorded over the past seven days (July 13-19, 2017) are presented below.
The growing degree day map (GDD) (Base 10ºC, March 1 – July 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.
Wheat Midge (Sitodiplosis mosellana) – Reminder – The previous Insect of the Week (Week 7) features wheat midge!
Model output indicates that the emergence of adults is well underway across the prairies. Oviposition should be underway and larvae should be present. Dry conditions in Saskatchewan appear to have reduced potential adult emergence.
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.
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.
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.
Grasshopper Simulation Model Output – Based on model output, development is slightly ahead of long term normal (LTN). Grasshoppers should be predominantly in the third and fourth instar stages with more rapid development across southern Alberta. Last week the mean instar was 3.4; this week it increased to 4.1.
Figure 1. Predicted Melanoplus sanguinipes development across the Canadian prairies (July 16, 2017).
Figure 2. Predicted Melanoplus sanguinipes development prepared using Long Term Normal (LTN) data.
Figure 3. Predicted percent of Melanoplus sanguinipes at fifth instar development stage (July 16, 2017).
This is the first week where the model has predicted appearance of adults. As of July 16, 2017 adults should be occurring across 45% of the prairies (compared to long term average value of 39%).
Figure 4. Predicted percent of Melanoplus sanguinipes at adult stage (July 16, 2017).
Grasshopper Scouting Steps:
● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin.
● Starting at one end in either the field or the roadside and walk toward the other end of the 50 m making some disturbance with your feet to encourage any grasshoppers to jump.
● Grasshoppers that jump/fly through the field of view within a one meter width in front of the observer are counted.
● A meter stick can be carried as a visual tool to give perspective for a one meter width. However, after a few stops one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance.
● At the end point the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure. ● Compare counts to the following damage levels associated with pest species of grasshoppers:
0-2 per m² – None to very light damage
2-4 per m² – Very light damage
4-8 per m² – Light damage
8-12 per m² – Action threshold in cereals and canola
12-24 per m² – Severe damage
>24 per m² – Very severe damage
* For lentils at flowering and pod stages, >2 per m² will cause yield loss.
* For flax at boll stages, >2 per m² will cause yield loss.
Diamondback moth (Plutellidae: Plutella xylostella) – Once the 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.
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).
Across the prairies, provincial staff coordinate diamondback pheromone trapping during the growing season: ● Counts will be reported by the provincial staff in Saskatchewan. ● Manitoba Agriculture and Rural Initiatives posted low DBM counts which can be reviewed here. ● Alberta Agriculture and Forestry has a live 2016 map reporting Diamondback moth pheromone trap interceptions. A copy of the map (retrieved July 20, 2017) is below for reference.
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 #9 (posted July 19, 2017) noting the continued presence of thistle caterpillar (Vanessa cardui) and their webbing in some soybean fields, aphids in some cereal and pea fields and diamondback moth near the economic threshold in some canola fields in the Central region. Reminder – Cumulative counts of bertha armyworm generated from weekly counts in Manitoba can be accessed here.
● Saskatchewan’s Crop Production News – 2017 – Issue #4includes information related to soybean pestsprepared by Joel Peru. That report includes an update on scouting and management tips for painted lady butterflies (also described in Week 6) and Aphanomyces root rot.
● Watch for Alberta Agriculture and Forestry’s Call of the Land and access the most recent Insect Update (July 20, 2017) provided by Scott Meers. That report notes emergence of second generation of painted lady butterflies (V. cardui) which should be monitored closely in borage, soybeans and any plant in the sunflower family, but also watch volunteer thistle in canola since the larvae will move onto the latter if the thistle is consumed. Both cabbage butterfly and yellowish imported cabbage worm butterflies are active and laying eggs in cabbage and canola in that province. The wheat midge flight is nearly done but continue to scout late wheat that is still flowering. Finally, pea leaf weevil and cabbage seedpod weevil numbers appear to be lower in 2017 compared to 2016 which is good news.
Active Wildfires – Natural Resources Canada posts live interactive maps like the one below. Access their webpage for more information and to stay current on the various active wildfires burning across Canada.