INDISPENSIBLE INSECT COUNTS
BY IAN DOIG • PHOTOS COURTESY OF SHELLEY BARKLEY
Those orange and red, blob-like areas on insect survey maps are a farmer’s cue to action. Fields seeded with certain crops and located in and around these hotspots may require individual assessment and population control. Among cereal farmers, the most anticipated of these maps are those for grasshoppers, wheat stem sawfly and wheat midge.
Prairie Pest Monitoring Network (PPMN) grasshopper survey work is carried out by collaborators from Agriculture and Agri-Food Canada (AAFC), the three Prairie provincial agricultural departments and the Saskatchewan Crop Insurance Corporation (SCIC), agricultural fieldmen and additional volunteers.
Each summer, agricultural fieldmen, who work for Alberta’s Agricultural Service Boards, conduct counts along road allowances within every Alberta municipality. This data is then processed by Shelley Barkley, an Alberta Agriculture and Irrigation insect technologist. It is then forwarded to Meghan Vankosky, AAFC entomology research scientist and PPMN co-chair. In Saskatchewan, SCIC conducts most sampling and Manitoba’s ag ministry co-ordinates sampling in that province.
To estimate population density per square metre in late summer and early fall, surveyors walk fields and note the number of grasshoppers that take flight. The abundance of various species is also noted. Collected data is compiled to create the annual grasshopper risk map, or forecast map.
The PPMN also maintains sites where it conducts grasshopper counts throughout the summer to follow the development of grasshopper populations from nymph to adult. During the growing season, this information is updated weekly at prairiepest.ca.
In Alberta, ideal grasshopper conditions prevailed from August through early October 2022. “In general, the further south we travelled, the higher the grasshopper population densities got,” said Vankosky. “We generally expect that high densities in the fall translates to higher risk going into spring 2023.” The grasshopper map indicates a hotspot southeast of Lethbridge, but grasshopper density is generally high south of Calgary.
In contrast to the south, Vankosky suggested farmers north of Edmonton and into Peace Country be vigilant in 2023, even though grasshopper numbers in the region were low in 2022. Associated with the Prairie treeline, Bruner’s grasshopper appears to be on a unique odd-year cycle and its population is less predictable than other pest grasshopper species. “This every-second-year trend is not always captured in the survey,” said Vankosky. “This could be a year, again, where we do see higher numbers of Bruner’s grasshopper.”
She also suggested farmers across the Prairies scout for grasshoppers early and often this spring, especially if weather is dry and warm. “Grasshoppers respond very well to those conditions, and that will contribute to increased risk.” The best time to kill grasshoppers is when they’re young as they are smaller and less mobile, she added.
WHEAT STEM SAWFLY
Barkley oversees the fall survey of wheat stem sawfly, an insect of special concern to farmers in southern Alberta. The annual two week project is conducted on 100 farms south of Highway 9 through to the U.S. border and from Pincher Creek to the Saskatchewan border. In five fields per county, surveyors calculate the ratio of cut stems to uncut in four one-metre row sections per field. Hotspots with greater than 25 per cent cut stems appear in red on the risk map. “Wheat stem sawfly really does well in the County of Forty Mile,” said Barkley.
The 2022 survey found fewer high-density areas than in 2021, but the insect was found in more fields across a greater area. A single infested field was identified in Knee Hill County north of Highway 9.
Though sawfly flourished in the heat of 2021, Bracon cephi, the parasitic wasp known to keep its numbers in check, did not. Its population may yet be on the rebound. The wasp overwinters high in the wheat stem, while the sawfly migrates to the crown and can even settle in below soil level. Farmers in sawfly territory tend to cut wheat higher. The use of a stripper header allows the beneficial wasp to overwinter.
With little effective insecticide available, additional cultural controls are necessary. Farmers in the area grow solid stem wheat, adjust their rotations and seed larger fields. Barkley also encourages farmers to do their own counts. Pick four one-metre row sections along the field margin and count both cut and uncut stems. The damage can be visually striking, but the percentage of affected plants is difficult to gauge by eye. “This will give you a better understanding of what’s going on in your field,” said Barkley.
“We’re very fortunate wheat midge has one of the most robust pest management monitoring plans,” said Jennifer Otani, AAFC pest management biologist and PPMN co-chair.
Very dry conditions in 2021 may have caused the midge population to lie dormant that year. Cocoons were then prevalent enough in 2021 and 2022 wheat crop soil cores to cause concern in spring 2022. “We had almost perfect growing conditions for the midge cocoons,” said Otani. “And portions of the Prairies also had nearly perfect wheat development staging, such that midge emerging overlapped with heading in wheat.”
Once harvest is complete, Alberta Agriculture’s Barkley collects soil cores from approximately 325 spring wheat fields across Alberta. The annual survey samples three to six fields per county, including dryland and irrigated acres. At the Crop Diversification Centre South in Brooks, Barkley assesses the density of cocoons and whether they have been parasitized by Macroglenis penetrans, a tiny beneficial wasp. Alberta and Saskatchewan ag ministries and PPMN publish midge risk maps online each January.
“Based on those maps, farmers can decide whether they’re going to go with midge resistant cultivars,” said Otani.
In spring, Vankosky and her PPMN colleagues continue to assess midge populations, which are very sensitive to early season conditions. They refine the forecast with the incorporation of Prairie environmental data to their modelling.
Additional monitoring is carried out by AAFC Saskatoon entomologist Tyler Wist with the help of SeCan clients. These farmers voluntarily deploy pheromone traps in wheat fields across the Prairies in late June and early July. This determines when the insects are on the move. Real-time activities of the trapping network can be tracked on Twitter at #midgebusters. “It’s a great educational tool to teach people about wheat midge,” said Wist. “It gives me a platform to answer questions directly.”
Proving the value of the project, a Peace Country farmer reported collecting a lot of male midge. Wist asked him to check the wheat heads for females, which held three per head. The economic threshold is one per five heads. The farmer rolled out the sprayer immediately. Launched in 2021, Wist hopes the initiative will continue in 2023 with the addition of larvae counts.
Dry conditions kept midge numbers low in 2021, but the insect rebounded. “In 2022, we learned you don’t turn your back on wheat midge even if a bad year is not in the forecast,” said Wist. “If conditions are right, they come roaring back.”
“That program really helps producers time their in-field scouting,” said Otani. “We’re able to predict on a regional basis, but they can then follow up field by field.”
Alberta Agriculture offers midge pheromone traps to Alberta farmers and agronomists. Users contribute counts to an accompanying app. This data on the insect’s prevalence and development fuels a live-feed map available at the Alberta Insect Pest Monitoring Network webpage. The map facilitates greater effectiveness in field scouting. Pheromone trap use is on the rise, said Barkley, especially in areas where the insect is most common, such as Beaver County and the Highway 16 corridor between Edmonton and Lloydminster.
The fall 2022 midge survey indicated a mostly positive outlook. In the southern irrigation areas where moisture levels can benefit the insect, none were detected. Just two fields were found to contain midge in Flagstaff County in 2021. The area tends to receive more moisture than dryland acres to the south, and midge did expand significantly across Flagstaff, Camrose and Beaver counties in 2022. A few were also found in Sturgeon County.
Barkley suggested farmers in affected areas monitor their fields closely when wheat crops are at heading and are most susceptible to midge damage.