Crop & Pest Report


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Sugarbeet Root Maggot: Fly Activity Dropping, Watch Out for Resurgence (06/14/18)

Sugarbeet root maggot (SBRM) fly activity has diminished considerably in the past few days.

Sugarbeet Root Maggot:  Fly Activity Dropping, Watch Out for Resurgence

Sugarbeet root maggot (SBRM) fly activity has diminished considerably in the past few days.  This is, in part, due to wet and windy weather that began last Friday.  Such conditions keep flies down in more sheltered microsites, such as on the ground, in the plant canopy, and in field margins.  The adults also fly at lower distances above the ground, resulting in many flies being missed by sticky-stake traps, or the majority being captured on the lower end of the sticky surface of the trap (Fig. 1).  As such, the fly infestation actually present in a field may not always be accurately estimated by sticky-stake traps. 


Peak fly activity has probably been surpassed in all areas of the Red River Valley (RRV).  Populations are expected to continue dropping in the coming days.  However, as warmer and more settled weather conditions resume, it will be important to closely monitor for any potential resurgences of fly activity in fields of concern. 

Valley-wide, SBRM fly infestations are on the increase in comparison to the past couple of years.  In fact, if monitoring results continue at the expected pace for the next week or so, 2018 will be the second-highest fly activity year in the past 12 years.  Hotspots this year include Auburn, Bathgate, Cavalier, Crystal, Drayton, Grand Forks, Reynolds, St. Thomas, and Thompson, ND, as well as Ada, Crookston, and E. Grand Forks, MN.

Two things to watch for.  First, a close watch should be kept on all fields in areas where at least moderate fly activity had been detected during the past two weeks.  A resurgence in activity could possibly require a rescue insecticide application (see Control Recommendation below).  Second, due to the extremely early flush of fly activity in several fields this year, plants in unprotected fields (or those where postemergence rescue insecticide applications were made later than optimal) could begin showing stress, and even dying, as warmer weather develops.  Adequate to even surplus soil moisture conditions may actually save some of those fields this year if regular rainfall events occur to sustain those plants.

Control Recommendation.  Fields should be monitored for fly activity during the next few days.  The areas of highest concern at this time are those in the central and northern RRV.  Fields that have already received a postemergence liquid spray may require retreatment if subsequent infestations reach or exceed 0.5 flies per plant.  NDSU research suggests that postemergence liquid insecticides are the best option for SBRM control at this time, and they still can provide good results if applied within 2-3 days after peak fly.  Fields protected with postemergence granular insecticides should be sufficiently protected, and should not need additional treatment.  Foliar liquid insecticide applications made after this weekend (June 19-21) are unlikely to be economically justifiable, unless infestations reach 0.5/flies 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-containing liquid can be made to the same field.  If retreatment is deemed necessary within 10 days of the initial chlorpyrifos application, an insecticide product containing a different active ingredient must be used.  For more guidance on postemergence control strategies, 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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