Dr. Erik J. Wenninger, Entomology and Extension Specialist with the University of Idaho at the Kimberly Research & Extension Center: Peak flight of root maggot flies.
The degree day calculator (hosted by the Integrated Plant Protection Center at Oregon State University) for the sugarbeet root maggot fly shows that—depending on your location in the Magic Valley—we have accumulated more than 360 degree days since March 1, 2012. Peak flight of root maggot flies should occur after 360 accumulated degree days when the maximum high temperature exceeds 80 degrees F. In the Mini-Cassia area, this usually occurs around the 2nd of June, but with warmer weather this year, peak flight in Rupert was predicted to have occurred on May 14.
Monitoring flies adjacent to your sugar beet fields using orange sticky stake traps will provide even more useful information regarding the local population densities of flies. The Amalgamated Sugar Company monitors flies with sticky stake traps throughout the Mini-Cassia area and posts the counts on their website: http://www.srcoop.com/ The economic threshold for application of granular insecticides against root maggots is an accumulative total of 40-50 sugarbeet root maggot flies per sticky stake trap (the threshold varies depending on your contract price per ton).
In the Mini-Cassia area, which historically has had high root maggot pressure, growers should consider an insecticide application 10 days before exceeding threshold captures on sticky stakes. Otherwise, insecticide applications should be made within 10 days before or after reaching the threshold (the closer to the threshold date, the better). Activation of granular insecticides should be accomplished by irrigation as soon after application as possible. See University of Idaho publication CIS 999, IPM Guide to Sugarbeet Root Maggot: http://www.uiweb.uidaho.edu/sugarbeet/insc/sbmaggot.htm
You can monitor degree day accumulation for sugarbeet root maggots as follows:
1) Log onto: http://uspest.org/cgi-bin/ddmodel.pl?spp=srm
2) Select “Sugarbeet Root Maggot Bechinski et al. 1990” degree day model from the “Select degree day model….” drop down box at the top of the form
3) In the “Select location” box, select a location in the drop down box best describing your location (e.g. “RUPERT id agmet” in the “Washington, Idaho” box if you want information for a field near Rupert). Make sure to select “None” at the top of the lists in the other two location boxes.
4) Leave the “Or upload your own…” box blank
5) In the “Forecast:” area, enter your zip code or your city, state in the “NWS zipcode/city, state” box, or the location nearest your field from the “or weather.com site” drop down box to the right). This selection forecasts 7 days forward based on the local weather forecast (beyond 7 days the forecast is based on the historical average). The predicted date of peak fly flight will vary depending on the forecast location selected, so pick the one closest to your location. Select “none” to have the forecast based only on the historical average.
6) Select the location nearest your field in the “Select historical average forecast location” area. Your selection here should match, as close as possible, your selection in the “Select location” area above: there may not be an exact match. As above, select “none” in the other two boxes.
7) Make sure the “Table” and “graph” boxes are checked (and the “precipitation” if you want rainfall information) and click the “Calc” button. A table with the current degree day accumulations matching your selection should appear. There should also be a graph near the bottom showing the current year accumulation compared to the historical average for your selections.
To view the full alert, and to download any attached files, please go to www.pnwpestalert.net