Crop & Pest Report


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Sugarbeet Root Maggot Activity: Windy Weather = No Sharp Peak, Many More Flies to Come (06/18/20)

Similar to the past two years, several areas in 2020 experienced substantial surges in sugarbeet root maggot (SBRM) flight activity ahead of “normal”.

Similar to the past two years, several areas in 2020 experienced substantial surges in sugarbeet root maggot (SBRM) flight activity ahead of “normal”. Fly activity gradually built up to what were considered high to severe levels in many of those fields.

Although flies are present in extremely high levels in many fields throughout the growing area, especially the northern RRV, the persistent windy weather (Fig. 1) during the past week has kept most flies down near/on the ground. As such, fly counts from the past few days are not reflective of the high fly densities present in many fields. Therefore, we can expect many more flies to emerge in the next few days. This will result in a very flat activity curve during peak fly activity which has been occurring during the past 3-4 days.


Cumulative fly counts are quite concerning this year, with the most severe counts being recorded in the northern Valley. Representative areas where the highest fly counts have been recorded are presented in Table 1. Daily and cumulative fly counts from all locations can be viewed online here.


Postemergence SBRM Control. Growers in high-risk areas for damaging SBRM infestations who have not yet made a postemergence insecticide application should do so as soon as possible, as the window for effective performance is closing. This is especially important if an insecticidal seed treatment or a low to moderate rate of a granular insecticide was used at planting. Fields in which heavy rainfalls (> 3 inches) occurred within two to three days after at-plant or postemergence insecticides were applied also may need additional postemergence protection.

The best control option this time is a sprayable liquid insecticide application, which can either be applied by ground-based equipment or aircraft. Postemergence liquid insecticides perform best if applied close to (within 2-3 days of peak fly; either on, before or after peak). Treated fields should be monitored closely for the next few days to determine if fly activity resurges. Some fields could require retreatment if subsequent infestations reach or exceed 0.5 flies per plant.

IMPORTANT: If a chlorpyrifos-containing liquid spray (e.g., Lorsban 4E, Lorsban Advanced, or any generic chlorpyrifos product) is applied, 10 days must pass before another chlorpyrifos liquid can be made to the same field. If retreatment is necessary within 10 days of the initial chlorpyrifos application, an insecticide containing a different active ingredient must be used. For more information, consult the “Insect Control” section of this year’s Sugarbeet Production Guide. Always remember to READ, UNDERSTAND, and FOLLOW the label of your insecticide product – it’s the law.


Mark Boetel

Research & Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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