Roadside Spraying

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The primary goals of roadside spraying in Dallas County are motorist safety and noxious weed control. Motorist safety is accomplished by total vegetation control around bridge abutments and guardrails, as well as brush control in the Right-of-Way. Brush control in the ROW ensures a recovery zone for motorists and provides adequate sight distance near signs, intersections and curves. It also helps prevent snow drifting and icing of the road surface.


Multiple tools are used by IRVM staff for herbicide application. The primary application method utilizes a Spratronics injection-type sprayer. It is the main tool of the spray crew and is used to spray at least one-half of the roads for weeds and brush annually. One quadrant of the county is covered in the spring/early summer months (e. g. NW, NE, SE, SW) and another quadrant is covered in the fall. This Spratronics machine is equipped with a differential GPS unit and two computers, one of which controls the amount of chemicals being applied and another which allows for precise recording of weed patches and amounts of chemicals applied.

A utility vehicle (UTV) is a supplemental tool for weed control and is used primarily on weed “complaints” originating from either private citizens or roads staff. We find it more efficient to use this machine to address these reports rather than pulling the Spratronics unit away from the area of the county that it is being focused on at the time. The UTV has also proven to be valuable in treating areas inaccessible to the Spratronics because of ROW width or other factors.

Bareground Spraying

To help prevent accidents around bridge abutments and guardrails, total vegetation control ( i.e. bareground spraying) is utilized. Every spring, the vegetation and soil are treated around all county bridges, 39 with guardrails and 91 with abutments. Due to the persistence and non-selective nature of the herbicides used, only the minimal area needed to ensure motorist safety is treated.

Brush Control

The Secondary Roads Department uses a variety of equipment to control brush, including chainsaws and mowers. However, these methods can be very labor intensive and costly. Without chemical treatment of the stumps, many species of trees quickly resprout with multiple stems which can exacerbate the problem. Careful spot spraying of brush using the appropriate method often results in a more efficient and cost-effective control than by mechanical means. Depending on the location of the problem, time of year and species, one of three herbicide treatments is used:

  • Basal-bark treatments are used from late fall to early spring on deciduous trees smaller than six inches in diameter. A low volume of herbicide/basal-oil mix is applied around the lower six to eighteen inches of the tree trunk.
  • Foliar treatments involve applying herbicide to the leaves of trees and brush and are typically used on smaller trees (<15ft.) from late spring to early fall.
  • High Volume Foliar (HVF) treatments are an excellent option when a problem area exists near water or sensitive crops. They are also used in areas where the previous techniques are not practical. Dallas County's HVF treatments involve using a low concentration of a practically nontoxic anti-budding agent that prevents the buds from opening up the following spring.

Weed Control

Noxious and invasive weed species are also being managed with herbicides. Two species of noxious weeds that are most prevalent in the county and therefore most focused on are musk thistle (Carduus nutans) and Canada thistle (Cirsium arvense). Other noxious species that are being managed include: bull thistle (Cirsium lanceolatum), tall thistle (Cirsium altissimum), teasel (Dipsacus spp.), leafy-spurge (Euphorbia esula), and purple loosestrife (Lythrum salicaria). Japanese knotweed (Polygonum cuspidatum), which is highly invasive but not yet classified as a noxious weed under Iowa law, is also being controlled.

Species that are not declared noxious but are declared nuisance weeds by the Dallas County IRVM program for various reasons include: Marijuana (Cannibus sativa) and Giant Ragweed (Ambrosia trifida).

No Spray Policy

It is currently the policy of Dallas County IRVM not to spray the right-of-way directly in front of houses and outbuildings. However, if you desire that Dallas County spray crews not treat a specific locale outside these areas, we ask that you register your NO SPRAY area with us by completing a NO SPRAY request form.

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