Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky
Weather synopsis – This past week (June 11 – 18, 2018), the average temperature (12.4 °C) was 1 °C cooler than long term average values (Fig. 1). The warmest weekly temperatures occurred across Manitoba. The 30-day (May 19-June 18, 2018) average temperature (13.1 °C) was approximately 1 °C warmer than long term average (Fig. 2).
Weekly and 30-day total precipitation was above average (Figs. 3 and 4). The wettest (30-day) region was across eastern areas in SK and western MB, while western Saskatchewan and most of Alberta are dry.
Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper).
As of June 18, 2018, the model output indicated that the average instar was 2.1 this week (1.7 last week), with 23, 27, 25, 8 and 2% in the 1st, 2nd, 3rd, 4th and 5th instar stages, respectively. The most rapid grasshopper development was predicted to occur across southern Manitoba and southeast Saskatchewan (Fig. 8).
Model output for Saskatoon illustrates that populations are primarily in the 2nd and 3rd instar stages with 4th and 5th instar stages beginning to appear (Fig. 9). This agrees with this week’s survey conducted between Saskatoon and Rosetown. Melanoplinae adults were collected at a few sites near Saskatoon and eastern Saskatchewan.
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.
Bertha armyworm (Lepidoptera: Mamestra configurata) – BAW development continues to be 7-10 days ahead of normal development (Figs. 1 and 2). Near Saskatoon, oviposition is predicted to be well underway (Fig. 1).
Based on climate data (LTCN), oviposition near Saskatoon should begin the third week of June (Fig. 2).
Many thanks to those who are checking a bertha armyworm pheromone trap on a weekly basis. Please use the reference photo below kindly shared by Saskatchewan Agriculture to aid your identification and reporting of trap interceptions. Note the kidney-bean white-patterned shape on each forewing but also know other cutworm species can resemble bertha armyworm moths. Check carefully and thanks for your help!
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:
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.
Keep track of the Provincial Entomologist Updates for the latest in-season pheromone trap monitoring results for 2018.
Albertans can access the online reporting map (screenshot retrieved 19Jun2018 provided below for reference:
Wheat Midge (Sitodiplosis mosellana) – Recent dry conditions near Saskatoon have resulted in slower wheat midge development (compared to last week’s model output). Predictions for 2018 (Fig. 1) are similar to long term average values (Fig. 2).
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.
The 2018 wheat midge forecast map was circulated in January and is posted below for reference. Note that areas highlighted orange or red in the map below included surveyed fields with comparatively higher densities of wheat midge cocoons last fall.
Lygus bugs (Lygus spp.) – The model indicated that Lygus populations range between the 1st – 4th instar stages with the average being second instar stage. The greatest development is predicted to occur across southern Manitoba and Saskatchewan (Fig. 1). The model suggests that Saskatoon populations consist of first to third instar stages (Fig. 2).
Remember – 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.
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.
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-enhanced or French-enhanced versions are available.
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!
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).
Across the prairies, provincial staffs coordinate diamondback pheromone trapping during the growing season. Every spring, the early arrival of diamondback moths (Fig. 3) is monitored through the tracking of high level air masses that originate from the south of North America and arrive across the Canadian prairies. Additionally, pheromone traps are deployed to intercept the initial moths. Cumulative male moth counts occurring over a 6-7 week period of trapping are used to estimate relative risk for the growing season. Vast networks of cooperators across Manitoba, Saskatchewan, Alberta, and the BC Peace work with their provincial entomologists to generate the following in-season results:
● Counts are summarized by Saskatchewan Agriculture (updated June 15, 2018, by J. Tansey):
● Manitoba Agriculture generally reports low DBM counts so far but review the specifics by region within the latest Insect and Disease Update (June 6, 2018).
More information about Diamondback moths 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 Diamondback moth page 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.
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.
Reminder – The 2017 cabbage seedpod weevil distribution map was circulated in January and is posted below for reference. Note that areas highlighted orange or red in the map below included fields with comparatively higher densities of the weevil in 2017 so in-field scouting is particularly important in these same areas in 2018.
If larvae are encountered in 2018, please carefully collect 20-30 of them and put them with some cereal leaves and a moist paper towel in a hard container (e.g. plastic yogurt container) with holes poked in the lid for air. Pack the parcel with ice packs, label with your name, date, crop type, and location, and send them to us. Email or phone us for information on how to ship for free.
What’s in it for you? Learn if cereal leaf beetle is being controlled by natural enemies in your field. If you need T. julis, we may be able provide you with some.
Pea Leaf Weevil (Sitona lineatus) – The PLW model predicted that larvae should be appearing in fields near Saskatoon (Fig. 1). Development in 2018 is faster than that predicted using long term averages (LTCN presented in Fig. 2).
Larvae develop under the soil over a period of 30 to 60 days. They are “C” shaped with a dark brown head capsule. The rest of the body is a milky-white color (Fig. 3 A). Larvae develop through five instar stages. In the 5th instar, larvae range in length from 3.5 – 5.5 mm. First instar larvae bury into the soil after hatching, and search out root nodules on field pea and faba bean plants. Larvae enter and consume the microbial contents of the root nodules (Fig. 3 B). These root nodules are responsible for nitrogen-fixation, thus pea leaf weevil larval feeding can affect plant yield and the plant’s ability to input nitrogen into the soil.
Scarabaeidae – Reminder – Each June brings scattered reports across the Prairies of white grubs associated with crop damage. In fact, several species of Aphodius, Phyllophaga, Polyphylla or even small Aetenius produce larvae described as “white grubs”.
Recently, crop damage reports have been associated with a grub identified as the larvae of the beetle Aphodius distinctus (see below). This common beetle is not known to be a pest, but there is an ongoing effort to gather information to develop a ‘pest’ profile. Additional information is online at Top Crop Manager. Please send reports of this insect and associated information to Dr. Kevin Floate (Agriculture and Agri-Food Canada, Lethbridge, AB).
What a difference a year makes! The Field Heroes campaign has been successful at raising awareness of the role of beneficial insects in Western Canadian crops. You’ll see this year’s campaign giving growers and agronomists more details on the many natural enemies they should be scouting for in cereal, oilseed and pulse crops.
Please make use of the Scouting Guides freely available on the Field Heroes website. Each guide includes valuable information and photos to help identify the contents of a sweep-net and to increase understanding of the impact of beneficial insects. Please share and encourage use of the Scouting Guides.
Be sure to follow @FieldHeroes on Twitter for practical tips and information. Please tag @FieldHeroes in your own Tweets about beneficials. Re-Tweets are great, too.
Thanks to Western Grains Research Foundation for their support of this important campaign. This initiative is not possible without the support and advice of enthusiastic members of the Prairie Pest Monitoring Network. Our research is having a tangible impact on growers’ pest management decisions.
Provincial entomologists provide insect pest updates throughout the growing season so we link to their most recent information:
Manitoba‘s Insect and Disease Update for 2018 can be accessed here. Review the most recent update (June 6, 2018) prepared by John Gavloski and Holly Derksen. The insect update notes flea beetles in canola and cutworms with monitoring for alfalfa weevil larvae underway. Diamondback moth trap numbers remain low and bertha armyworm pheromone traps will go up this week.
Alberta Agriculture and Forestry’s Call of the Land regularly includes insect pest updates from Scott Meers. The most recent Call of the Land (posted on June 21, 2018) noting that bertha armyworm moths were detected this first week of pheromone monitoring (check online map), onset of flowering in canola signalling the need for in-field monitoring for cabbage seedpod weevil, continued grasshopper calls from the south and advice to scout now while nymphs are easier to manage, Nutall’s blister beetle transiently showing up in some fields (blister beetle post), and the presence of the beneficial stiletto fly larvae which is a predator within the soil profile and targets wireworm larvae.
We continue to track the migration of the Monarch butterflies as they move north by checking the 2018 Monarch Migration Map! A screen shot of the map has been placed below as an example (retrieved 21Jun2018) but follow the hyperlink to check the interactive map. They are in Manitoba and moving west through southern Saskatchewan this week!
This week’s Insect of the week is the red turnip beetle (Coleoptera: Chrysomelidae). This beetle is 7-10 millimeters long and has a distinctive red body with black markings on the head and thorax, and three black stripes down its back (elytra). They feed on mustards, canola, cole crops, and cruciferous weeds (except stinkweed).
They overwinter as reddish brown oval eggs in the soil. Adults emerge in the spring to feed for 2-3 weeks before re-entering the soil to escape the summer heat. When they re-emerge, they disperse throughout the host crop, feeding, mating, and laying eggs (300-400/female). Feeding damage can cause delayed harvest or need for re-seeding to replace killed plants. Later in the season they feed on leaves, stems, and pods. Attached pods are prone to premature shelling.
For more information about the red turnip beetle, have a look at our Insect of the Week page!