By Carter Peru, B.Sc., A.Ag
Once again, a variety of insect pest surveys took place during the 2020 growing season in Saskatchewan. The surveys are important tools for creating forecast and population density maps, to inform in-season monitoring, and to support research. Here is a snapshot of a few of the surveys conducted in 2020.
Diamondback Moth Survey
Diamondback moths (DBM) were monitored at 45 pheromone traps that were set up across the province. This is the earliest insect survey conducted, with traps set up at the end of April. DBM is a pest of concern in many brassicaceous crops, including canola and mustard. Each week, traps are checked and surveyors count how many diamondback moths were caught. The ministry provides these updates during the monitoring season. Since diamondback moths do not overwinter in significant numbers in Saskatchewan, populations here depend on overwintering populations in the south (U.S. and Mexico) and their arrival to Saskatchewan as adults on strong wind currents. This year, overall cumulative counts were low, but some sites had higher counts. The highest cumulative count was seen in the Meadow Lake area, where 521 diamondback moths were caught. The Cadillac area had the second highest cumulative moth count at 151. Trap counts cannot be used to predict crop damage, but do provide an early warning of the presence and abundance of the moth. The larval stage of diamondback moth is the stage that causes crop damage, so scouting for the larvae must be done in order to determine the potential for crop damage and to apply economic thresholds.
Bertha Armyworm Survey
The bertha armyworm survey also uses pheromone traps placed in canola fields to attract and capture male moths across all canola growing regions of the province. Surveyors monitored 287 traps from mid-June until early August, submitting count numbers weekly. These counts are used to create cumulative moth count maps. These maps are then used as a risk indicator for bertha armyworm infestations. Adults do not cause crop damage, which means scouting for the damaging larvae stage is necessary to determine if the economic threshold has been reached. Determining these larvae, taking note of any beneficial insects that may already be attacking bertha armyworm and controlling the population are important steps to take before making the decision to spray. Bertha armyworm larvae can feed on many crop species, including canola, mustard and alfalfa. In 2020, overall cumulative moth counts were low for most of the province. High numbers of moths were seen in a small area in the east central region of the province near Humboldt. Moderate amounts of moths were also caught in a small area north of Saskatoon, as well as in the southeast near Wolseley.
Pea Leaf Weevil Survey
The pea leaf weevil survey assesses field pea crops for damage caused by the insect. Pea leaf weevil cause a distinct “c” shaped notch when they feed. The amount of feeding notches is recorded and used to create the annual pea leaf weevil map. The map shows the levels of notching damage, providing a good indication of populations and their distribution in the province. Primary host crops for pea leaf weevil are faba bean and field pea. Although notching damage is a useful way to monitor pea leaf weevil populations, notching damage does not usually cause yield loss. The primary damage is during the larval stage. Larvae feed on nitrogen fixing nodules, reducing the amount of nitrogen the crop can fix. The most effective chemical control option is an insecticidal seed treatment. Results of the 2020 survey show that pea leaf weevil feeding damage was very low overall. Moderate increases were observed in the far south and near Yorkton, in comparison to 2019.
Grasshoppers are considered a pest under The Pest Control Act – Pest Declaration Regulations. The grasshopper survey begins at the end of July to mid-August, when a majority of grasshoppers are in the adult stage. Only adult grasshoppers are counted, since they are considered the greatest reproductive threat to next year’s population. Surveyors count adult grasshoppers in ditches which may be alongside any crop type. Approximately 1200 sites are surveyed for population densities. The data is compiled to create a forecast map for the following growing season. The map depicts grasshopper densities calculated during the survey. In 2020, higher densities were observed near Birsay and Dinsmore. Moderate counts were observed in some areas of west-central Saskatchewan and southwest Saskatchewan.
Survey Maps Still to Come
Work associated with insect surveys conducted in the summer of 2020 is still ongoing. This includes sample analysis from the cabbage seedpod weevil and wheat midge surveys. Once samples have been analyzed, the data will be used to create additional maps. The cabbage seedpod weevil population density map, which is based on the number of adults captured through the use of sweep nets, provides an indication of 2021 cabbage seedpod weevil populations. During the wheat midge survey, soil samples are collected and later analyzed for the presence of wheat midge pupae. The data is used to create a forecast map for the following year.
This article was originally published in Agriview.