This week’s Insect of the Week is the cereal leaf beetle. Wheat is their preferred host, but they also feed on oats, barley, corn, rye, triticale, reed canarygrass, ryegrass, fescue, wild oats, millet and other grasses. Adults and larvae feed on the leaf tissue of host plants. Yield quality and quantity is decreased if the flag leaf is stripped. It is also interesting to note that larvae carry all of their own fecal waste with them as protection from predators.
Ross Weiss, David Giffen, Owen Olfert and prairiepest_admin
Weather synopsis – Although temperatures were warmer than last week, both the seven- and 30-day average temperatures were similar to long term averages.
Compared to 30-day average temperatures, Alberta was above normal, whereas Saskatchewan and Manitoba were slightly below normal.
Central and northern regions of all three provinces reported increased rainfall amounts. Total 30-day rainfall accumulations indicate that conditions are normal to dryer than normal for most of the prairies.
Growing season (April 1 – July 10, 2017) percent of average precipitation is average for most of Alberta and below average for most of Saskatchewan and Manitoba.
The lowest temperatures across the prairies over the past seven days (July 5-11, 2017) are mapped below.
In contrast, the highest temperatures recorded over the past seven days (July 5-11, 2017) are presented below.
The updated growing degree day map (GDD) (Base 5ºC, March 1 – July 9, 2017) is below:
While the growing degree day map (GDD) (Base 10ºC, March 1 – July 9, 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.
Bertha armyworm (Lepidoptera: Mamestra configurata) – Bertha armyworm should be in the adult stage across the prairies this week. The map illustrates predicted appearance of adults (percent of the population) across the southern prairies.
For those monitoring BAW pheromone traps, compare trap “catches” to the following reference photo kindly shared by Saskatchewan Agriculture:
Wheat Midge (Sitodiplosis mosellana) – Reminder – The previous Insect of the Week (Week 7) features wheat midge!
Model output indicates that wheat midge adult emergence has begun across the prairies. Cooler, dryer conditions in 2017 have resulted in lower emergence than the same time last year. Elliott et al. (2009) reported that adult emergence was delayed by inadequate rainfall amounts (May and June). The model was parameterized to take rainfall into account. Model output indicates that midge emergence across most of SK has been limited by inadequate rainfall during June.
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 – Compared to last week, grasshopper development has progressed by approximately one instar (Fig. 1). Based on model output, grasshopper development is slightly ahead of long term averages (Fig. 2).
Figure 1. Predicted Melanoplus sanguinipes development across the Canadian prairies (July 4, 2017).
Figure 2. Predicted Melanoplus sanguinipes development prepared using Long Term Normal (LTN) data.
Across the prairies, grasshoppers should be predominantly in the third and fourth instar stages with more rapid development across southern Alberta (Fig. 3 and 4). This is the first week where the model has predicted appearance of adults. The greatest development was predicted to be across southern regions in all three provinces, particularly southern Alberta. Current developmental rates are well behind last year.
Figure 3. Predicted percent of Melanoplus sanguinipes at fourth instar development stage (July 10, 2017).
Figure 4. Predicted percent of Melanoplus sanguinipes at fifth instar development stage (July 10, 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.
Ross Weiss, David Giffen, Owen Olfert and prairiepest_admin
Alfalfa Weevil (Hypera postica) – Across the prairies, the model indicates that 95% of the population should be in the pupal stage. This week adults should be appearing at most locations. Output indicates that adult emergence is well underway at many southern locations (Brooks, Estevan) , while adult emergence at many central locations (Saskatoon) has begun over the last five days.
In terms of degree-day heat units, the map below reflects the predicted development of alfalfa weevil across the Canadian prairies.
Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon) and additional information can be accessed by reviewing the Alfalfa Weevil Page extracted from the “Field crop and forage pests and their natural enemies in western Canada – Identification and management field guide” (Philip et al. 2015). That guide is available in both a free English-enhancedor French-enhanced version.
John Gavloski, Scott Meers, Scott Hartley and prairiepest_admin
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 #7 (posted July 5, 2017) noting the presence of thistle caterpillar (Vanessa cardui) and larval populations of diamondback moth reaching economically significant levels in the southwest of that province. Cumulative counts of bertha armyworm generated from weekly counts in Manitoba can be accessed here.
● Watch for Alberta Agriculture and Forestry’s Call of the Land and access the most recent Insect Update (July 5, 2017) provided by Scott Meers. That report notes migration of painted lady butterflies which feed on thistles but also soybeans, sunflowers, and dry beans. Soybean and sunflower producers will need to carefully follow the development of a second generation of V. cardui as it could affect those crops by mid-July. Additionally, diamondback moth are more numerous than in previous seasons so careful scouting will be required during early pod stages in canola as that stage is the most susceptible to yield losses.
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 9, 2017, areas highlighted in yellow on the map below have accumulated sufficient heat for C. tarsalis to fly 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 6, 2017, 729 birds were examined and six have tested positive for West Nile virus in Ontario.