Jennifer Otani, David Giffen, Ross Weiss, Serge Trudel, Owen Olfert and Meghan Vankosky
We shift back into the more traditional end of the week release of the “Weekly Update”.
Thanks to David Giffen and Ross Weiss (AAFC-Saskatoon) who again have begun to stream data that enables the generation of the various predictive model updates on a weekly basis throughout the growing season. This week, their efforts include pea leaf weevil, alfalfa weevil, and grasshopper predictive model outputs.
Agriculture and Agri-Food Canada (AAFC) and Environment and Climate Change Canada (ECCC) have been working together to study the potential of trajectories for monitoring insect movements since the late 1990s. Trajectory models are used to deliver an early-warning system for the origin and destination of migratory invasive species, such as diamondback moth. In addition, plant pathologists have shown that trajectories can assist with the prediction of plant disease infestations and are also beginning to utilize these same data. We receive two types of model output from ECCC: reverse trajectories and forward trajectories.
‘Reverse trajectories’ (RT) refer to air currents that are tracked back in time from specified Canadian locations over a five-day period prior to their arrival date. Of particular interest are those trajectories that, prior to their arrival in Canada, originated over northwestern and southern USA and Mexico, anywhere diamondback moth populations overwinter and adults are actively migrating. If diamondback adults are present in the air currents that originate from these southern locations, the moths may be deposited on the Prairies at sites along the trajectory, depending on the local weather conditions at the time that the trajectories pass over our area (e.g. rain showers, etc.). Reverse trajectories are the best available estimate of the ”true” 3D wind fields at a specific point. They are based on observations, satellite and radiosonde data.
‘Forward trajectories’ (FT) have a similar purpose; however, the modelling process begins at sites in USA & Mexico. The model output predicts the pathway of a trajectory. Again, of interest to us are the winds that eventually end up passing over the Prairies.
Ross Weiss (AAFC), Meghan Vankosky (AAFC) and Serge Trudel (ECCC)
DATE: APRIL 24, 2019
Reverse trajectories (RT)
a. Pacific Northwest (PNW) – For the period of April 17-23, 2019, there have been 55 RT’s (originating over ID, OR and WA) that have crossed over prairie locations (Figs. 1 and 2). By comparison, for the period of April 10-16, 2019, there were 31 RT’s. The majority PNW RT’s have been reported to pass over southern AB. Since March 23rd, Lethbridge AB has reported the highest number of PNW RT’s (n=20), Beiseker AB (n=15) and Gainsborough SK (n=11).
b. Mexico and SW USA (TX, CA) – No trajectories, originating over Mexico or southwest USA have crossed the prairies for the period of April 17-23, 2019. Since March 23, 2019 there have been 5 reverse trajectories that originated over Mexico, CA and TX. All five occurred on April 7, 2019.
c. Texas and Oklahoma – No trajectories, originating over TX or OK have crossed the prairies for the period of April 17-23, 2019. Since March 23, 2019 there have been 18 reverse trajectories that have originated over OK and TX (Fig. 3). Most of these trajectories have crossed eastern SK and MB.
d. Nebraska and Kansas – No trajectories, originating over KS or NE have crossed the prairies for the period of April 17-23, 2019. Since March 23, 2019 there have been 18 reverse trajectories that have originated over KS and NE (Fig. 4).
In a continuing effort to produce timely information, wind trajectory reports will be available both DAILY and WEEKLY:
DAILY REPORTS, as they can be generated, will be put up as a downloadable PDF file on this page.
Pea Leaf Weevil (Sitona lineatus) – The PLW model was run for Lethbridge AB (Fig. 1) and Saskatoon SK (Fig. 2). Output suggests that PLW are beginning to become active.
Pea leaf weevils emerge in the spring primarily by flying (at temperatures above 17ºC) or they may walk short distances. Pea leaf weevil movement into peas and faba beans is achieved primarily through flight. Adults are slender, greyish-brown measuring approximately 5 mm in length (Fig. 3, Left).
The pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) but the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen. All species of Sitona, including the pea leaf weevil, have a short snout.
Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge. Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.
Reminder – The risk map for pea leaf weevils was released in March 2019. The map is based on the number of feeding notches observed in peas (Fig. 4).
Alfalfa Weevil (Hypera postica) – Degree-day maps of base 9°C are produced using the Harcourt/North Dakota models (Soroka et al. 2015). Models predicting the development of Alfalfa weevil (Hypera postica) across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae. Compare the following predicted development stages and degree-day values from Soroka (2015) to the map below (Fig. 1).
Alfalfa weevil (AAW) model runs indicate that oviposition may have begun in fields near Swift Current SK.
The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer”. The green larva featuring a dorsal, white line down the length of its body has a dark brown head capsule and will grow to 9mm long.
Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon). 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). The guide is available in both a free English-enhancedor French-enhanced version.
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).
Model runs were conducted for Lethbridge AB and Saskatoon SK. As of April 23, 2019, predicted development was 57% for both locations and is similar to long term average values. The following graph illustrates that gradual development has occurred during the past three weeks. Hatch is expected to occur in mid to late May.
More information can be found by accessing the grasshopper pages within the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” as an English-enhanced or French-enhanced version.