Calculating Degree-day Accumulations for
Sugarbeet Root Maggot Development
The formula
The formula for the daily sugarbeet root maggot degree days is:
Daily SBRM DD = (((Daily Max Temp °F + Daily Min Temp °F) / 2) - 47.5 °F
The upper threshold on the maximum temperature is 99 °F. Calculations begin on April 1. Peak fly activity of sugarbeet root maggot occurs under warm (about 80 °F), low-wind (less than 10 mph) conditions at about 651 DD. This typically occurs 2-3 days after reaching 600 DD.
Insecticide timing
The following table shows suggested timing to apply postemergence liquid or granular insecticides for three general areas within Red River Valley. Recommendations are based on a 15-year average (1995-2009) of root maggot fly activity and associated weather patterns in the Red River Valley.
| Target DD for Insecticide Applications | ||
|---|---|---|
| Liquid Insecticides | Granular Insecticides | |
| Northern RRV | 590-620 DD | 440-550 DD |
| Central RRV | 585-615 DD | 410-545 DD |
| Southern RRV | 580-610 DD | 400-540 DD |
IMPORTANT! The following factors can cause deviations from this average:
- Bare ground in maggot overwintering sites (e.g., late-planted small grain fields with little or no established plant canopy) can lead to accelerated insect development and earlier peaks in some fields.
- The following weather factors can delay/reduce
activity if they occur near the expected peak:
- Winds above 10 mph
- Persistent or heavy rainfall
- Cool (less than 70°F) temperatures
General recommendations
Granule Applications: apply at 6-14 days before expected SBRM fly activity peak.
Liquid Applications: apply at 2-3 days before expected SBRM fly activity peak.
What to do if an early flare-up in activity occurs
Sugarbeet fields with infestations exceeding 0.5 SBRM flies per plant (1 per 2 plants) should be treated immediately with a liquid insecticide application at its labeled rate, even if the area has not reached the suggested target DD for treatment. Closely monitor such fields for several days after the application, and repeat if counts return to the 0.5-fly/plant level.
Recommendations based on sticky-stake counts
Growers are encouraged to monitor SBRM fly activity on their farms with sticky stake traps. Unprotected fields with cumulative fly counts of 40 to 45 flies per stake should receive a postemergence rescue insecticide application. Fields initially treated with a granular or seed treatment should receive additive insecticide protection if counts exceed a cumulative average of 70 flies per stake.