Develop a county weed control program that provides:

An integrated approach to roadside vegetation management means relying on a variety of weed control methods: mechanical, biological, chemical and cultural. IRVM emphasizes cultural control — establishing and promoting healthy, native vegetation – and tries not to rely exclusively on herbicides for controlling weeds.

Establish Native Vegetation

Native vegetation is the cornerstone of IRVM. Plant the best-adapted vegetation and keep it healthy. Iowa native plants are naturally adapted to the state’s climate and growing conditions. They handle tough roadside conditions. Their tall growth and deep roots help prevent weeds. Keep the natives healthy with the use of prescribed fire.

Do Not Overuse Herbicides

Overuse of herbicides weakens all vegetation, making roadsides more susceptible to invasion by weeds. Overuse of herbicides also eliminates desirable and harmless broadleaf species that would otherwise reduce weed invasion by occupying the same niche sought by weeds. For these reasons IRVM promotes careful spot-treatment of weeds when using herbicides.

Consider Mowing

Mowing must be considered before resorting to herbicides. The effectiveness of mowing depends on target species and timing. The feasibility of mowing depends on roadside slope and available equipment. County road right-of-way is often not suited to tractors. Still, spot-mowing for weed control is encouraged and counties should look for ways to make this a more frequent and viable weed control option.

Pay Attention to Timing

Timing is key to successful vegetation management; the effectiveness of mowing and spraying depends on it. IRVM recommends hiring a full-time roadside manager as the best way to provide professional, proactive and systemic weed control.

Keep Goals Realistic

IRVM recognizes there is no such thing as total weed eradication, so have realistic goals. Accept the presence of some weeds and keep them at a manageable level. Weed species that post no real threat to agriculture or natural areas should be tolerated. Prioritize weed control efforts, beginning with highly traveled roads.

Annual Weeds 

Annual weeds have a one-year life cycle. They germinate, grow, flower, set seed and die in one year or less. They reproduce by seed only. Common roadside annuals include common ragweed and giant ragweed.

To Control:

• Mow prior to seed-set.
• Eliminate bare soil and disturbances to vegetation.

Biennial Weeds 

Biennial weeds have a two-year life cycle. In the first year a basal rosette (circular cluster of leaves on or near the ground) is produced. The second year a central flowering stalk elongates and the plant dies after seed maturation. Biennials spread only by seed. Common roadside biennials include musk thistle, bull thistle, poison hemlock, wild parsnip and wild carrot.

To Control:

Perennial Weeds

Perennial weeds can live for a few years or for many years. Some perennials reproduce only by seed; many spread by seed and a variety of underground reproductive structures. Control of these perennials may be very difficult because of their extensive root systems.

To Control:

Iowa’s noxious weed list is outdated. It includes several species that no longer pose a threat to agriculture, and it does not include certain plant species now considered troublesome in the state.

The state’s primary herbaceous (non-woody) roadside threats are listed in Table 2. Herbicides remain the most practical means of controlling these weeds in county road right-of-way.

Table 2: Iowa's Primary Roadside Threats and Herbicide Recommendations

Notes: The most commonly used brand names are shown here. Many of these products are now available under other (often less-expensive) labels.

Where Garlon (triclopyr) is noted, either Garlon 3A (amine formulation) or Garlon 4 (ester) can be used. Garlon 4 is usually more effective but in hot weather can volatilize, drift and affect non-target species. 3A is non-volatile and usually considered the best choice for hot weather.

Herbicide Labels

Labels explain how to use the product effectively while protecting yourself, non-target plants and the environment. Take time to read the labels; it may be the most valuable time spent in weed control.

Adjuvants

Adjuvants are often added to the herbicide solution to increase its effectiveness. These products are put in the water tank at labeled rates.

Iowa’s noxious weed list includes a few woody species and several non-listed trees and shrubs have become troublesome in non-agricultural land throughout the state. In roadsides, all trees and brush are potential safety hazards. The primary goal of county roadside tree and brush control is to provide safe roads for the traveling public. Safety goals include:

Most roadside tree and brush control is accomplished by mechanical or chemical means. A correctly timed prescribed burn can also control brush.

Refer to "Tree and Brush Control for County Road Right-of-Way," a 2002 Iowa Highway Research Board/UNI-IRVM publication, for complete brush control information. Herbicide recommendations from that publication — with updates  — are shown in the appendix.

Resisting outside pressure to apply more chemicals might require educating a landowner — or even a member of the board of supervisors — why it might be inappropriate to spray. The following points can be helpful when talking to someone whose weed control philosophy is based primarily on experience with row crops and lawns.

Most Counties That Provide Their Own Weed Control:

Benefits of Providing In-House County Weed Control:

In the early days of IRVM, many counties sent crews into the ditch equipped with backpack sprayers. They carefully spot-sprayed weeds. While this method provided good weed control with a minimal amount of herbicide, roadside managers soon learned they could not cover enough of the county.

Since then IRVM has helped drive the development of spray truck technology that delivers herbicides with the accuracy and control needed to live up to the program’s original principles — killing target species without weakening non-target species or putting too much chemical on the ground.

Progress has been made, not just with more responsive on/off control switches and multi-directional spray nozzles, but with systems that monitor flow, record data and greatly reduce operator exposure. As with any spray equipment, these systems are only as good as the person whose finger is on the trigger. The objective is still to spot-spray. Beware of getting comfortable and sitting too long in the cab. Be conscientious, stay alert and be ready to grab the handheld sprayer and walk to that distant shrub to treat it properly. Never underestimate the value of your own labor; sometimes it’s still best to put on the old backpack.

Roadside Manager Insights

We don’t spray shoulders, just bridge abutments and guardrails.

-Jim Uthe, James Devig, Dallas County, 2024

We don’t spray wild parsnip unless asked or if there’s a really rank patch. Unfortunately, if we tried to spray every parsnip plant we’d essentially be blanket spraying many areas. 

-Jim Uthe, James Devig, Dallas County, 2024

I publicize in the paper when we will start spraying, and encourage people to call me with locations of sensitive areas – gardens, bee hives, allergies, etc. I have “No Spray Zone” signs for willing landowners. 

-Jeff Chase, Des Moines County, 2024

Higher diversity roadsides are more robust, more resistant to weeds. Maintain high diversity even if you don’t have the opportunity to establish natives. Don’t spray species that are not creating problems.

-Wes Gibbs, Jones County, 2024

Our goal each season is to cover half the county for noxious weeds and the other half for brush. Most of the weed spraying is noxious thistles and teasel. When spraying brush, we try to cover areas in which brush and trees were cut the prior winter to catch any re-growth.  

-Wes Gibbs, Jones County, 2024

We have isolated patches of garlic mustard that get sprayed. However, what exists in the ditch is usually spill over from the woods. What makes it to the ROW is just the tip of the iceberg, so I don’t get too excited about chasing it down. We have plenty of parsnip that, historically, was sprayed every year. Still have plenty of it. We currently do not spray parsnip. 

-Wes Gibbs, Jones County, 2024

I mostly use the web or my sales rep for technical support. It’s too hard to maintain up-to-date, written information on the most effective herbicides for each species. But like anything else, the advice is only as good as the source.

-Josh Brandt, Cerro Gordo County, 2009

Counties typically used truck- or trailer-mounted chemical injection (high-end) or tank mix (basic) spray systems. The following is one county’s description of its two spray rigs. These fairly well represent the range of equipment available.

Our high-end unit is a Legacy 6000 chemical injection system from Mid Tech. This unit has a GPS to record the rate, type and amount of chemical used. We download that info to our desktop and print our reports. Our system has three injection pumps with three chemical tanks, and a 300-gallon water tank all on a skid for easy loading and unloading on the pickup. All the controls and the electric start are mounted in the cab on a computer stand. We have three bumper-mounted spray nozzles — 6 ft., 20 ft. and 30 ft. — and a hose reel with 300 ft. of hose in the back. We like this unit because we can easily switch chemicals to spray something else and one person can load and unload everything in less than an hour. A downside of this system — we can only use liquid chemicals, otherwise everything gets plugged up.

Our basic unit can also be loaded in the truck by one person. Just about any chemical can be used because it’s a tank mix system with an agitator in the tank. It has a 200-gallon tank, also on a skid, run by a 5 ½ HP motor. We have two nozzles, a 6 ft. and a 30 ft. on the right-front bumper. There is a hose reel in the back with 200 ft. of hose. There’s no GPS on this system, so we have to keep track of everything. We mounted switches in the cab to run the nozzles, but we have to get out to turn the system on and off.

Another type of truck-mounted spray system used in roadsides is an invert emulsion sprayer. Invert emulsion was developed to reduce herbicide drift and volatilization by producing large droplets of water surrounded by oil. The mayonnaise-textured droplets do not dry as fast as water, so leaf penetration is improved. Invert emulsion sprayers do not work with all types of chemical products; liquid formulations usually work best.

Bumper-mounted nozzles or raised, multi-section, nutating spray nozzles are typically used on county rigs. The following is one county’s description of both nozzle types:

A multi-section, nutating spray head allows a mindful operator to choose which section of the ditch to spray — in 2, 4 or 6 foot increments out to 30 feet. A system with multiple bumper-mounted nozzles can spray different distances too, but they tend to spray everything up to that distance. The mutli-section system uses less herbicide primarily by hitting a narrower band. But if operators of multi-section systems hit all seven switches every time they spray a single thistle — just to make sure they don’t miss — there won’t be much reduction in herbicide. Ultimately a good operator still makes the difference.

The backpack sprayer is the best way to reduce herbicide use and target specific invasive plants, especially in diverse wildflower plantings.

Anyone who applies pesticides for a county agency or other government entity must be certified. The Iowa Department of Agriculture and Land Stewardship-Pesticide Bureau administers the state’s pesticide applicator certification process. A description of this process — and related information — are in the appendix.

Roadside Manager Insights

We have an 800 gal tank. I like using a lot of water; bigger droplets = less drift.

-Jim Uthe, James Devig, Dallas County, 2024

Our spray rig came with an 8HP engine which failed due to a mechanic’s error and was replaced with an 11HP due to availability. It lasted 8 or 9 years and was replaced with a 13HP which lasted 8 or 9 years too. We are on our second 13HP now. Our pump is a Hypro centrifugal pump with an electric clutch.

-Jim Uthe, James Devig, Dallas County, 2024

The Legacy 6000 can be used as a datalogger and rate controller. When our old datalogger died, we just piggybacked the Legacy onto our existing rate controller because it was a lot less work than redoing everything.

-Jim Uthe, James Devig, Dallas County, 2024

We recommended a minimum of 2 chemical injection tanks, 1 brush, 1 thistle. We used to put 2,4-D in our third tank for use on large patches of various undesirable weeds (giant ragweed, hemp, crown vetch, parsnip, hemlock, etc.). Now we put a low rate (5 oz/ac) of Method herbicide in the third tank and use it in addition to our brush mix when spraying honeysuckle.  

-Jim Uthe, James Devig, Dallas County, 2024

Excellent, up-to-date information about invasive species and their control is available on the web. Take advantage of the following websites.

Weed and Invasive Species Information

Herbicide Information

• Herbicide Effectiveness on Invasive Plants in Wisconsin

Herbicide Suppliers

Herbicide Manufacturers & Reps

Herbicide Spray Equipment Companies