Sugarbeet Root Maggot Update: Fly Activity to Peak Within 10 Days (5/31/12)
Sticky-stake counts conducted through Monday, May 28 indicated that the following areas appear to be the most likely hotspots for this year: Auburn, Forest River, Reynolds, and St. Thomas, ND, as well as Euclid, MN. It should be noted that several other areas have the potential for producing relatively high infestations. Other areas of concern that have had moderate levels of fly activity this year include Borup and Crookston, MN. Daily and cumulative counts for all monitoring sites can be viewed at: http://www.ndsu.edu/entomology/. Just click on the “INSECT RESOURCES” link on the main page, and download the dated Adobe Acrobat (pdf) file.
Figure 1 shows degree-day accumulations for root maggot development and activity in the RRV growing area. According to 15 years of data in the RRV, peak SBRM fly activity takes place at about 650 DD. However, flight activity is significantly impacted by weather. Warm weather (around 80F), and calm to light wind conditions are most conducive to fly activity. Flies will remain relatively inactive in cool, rainy, or windy conditions.
To determine degree-day totals for fields in your area, consult the Root Maggot application on NDAWN at: http://ndawn.ndsu.nodak.edu/sugarbeet-root-maggot.html. The site also includes a “help sheet” with information on how to use the model, recommendations for whether insecticide applications are needed, and pointers on when to apply them.
An updated forecast for anticipated DD accumulations and associated peak fly activity dates in the southern, central, and northern RRV is presented in Table 1.
Growers in hotspots or high-risk areas for SBRM infestation should consider applying a postemergence insecticide, especially if an insecticidal seed treatment or a low to moderate rate of an at-plant soil insecticide was applied. Postemergence granules are usually effective if applied between 2 weeks to 5 days before peak fly activity, but will also likely be beneficial if applied within 1-2 days before or after peak. Light to moderate rainfall after granular applications typically improves performance. Postemergence liquid insecticide applications should be targeted for peak fly activity, but will provide good results if applied within 2-3 days before or after peak. As Table 2 indicates, there is still plenty of time to apply either a granular or liquid insecticide for SBRM control this season.
For more guidance on postemergence control strategies, consult the “Insect Control” section of the 2012 Sugarbeet Production Guide or the “Sugarbeet Insects” section of 2012 Field Crop Insect Management Recommendations. Online versions of these publications are located at:
Research & Extension Entomologist