Iowa's Herbaceous Roadside Vegetation Threats

Iowa's Herbaceous Roadside Vegetation Threats thompsbb

Iowa’s noxious weed list is outdated.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

Species

Roadside Manager Recommendations (2011)

Application Schedule and Notes
(refer to product label for recommended rates)

Canada Thistle
perennial
  • Milestone
  • Transline (early season)
  • Telar (late season)
  • Transline/Telar (mid-season)
  • Perspective

Most effective control: Bud to bloom, or late fall just before frost; mowing increases efficacy of fall treatments. Growth stage is key, so treatment can be flexible:

  • We've had success killing thistles with Milestone in early-August if they were mowed in June/July and have adequate regrowth.
  • We've also had good luck with Milestone after hard frosts, as late as the last week in October. As long as it's green in the fall, spray it! Volatility may be an issue with Perspective in the summer.
Musk Thistle
biennial
  • Milestone
  • Opensight
  • Escort XP
  • Transline
  • Garlon
  • Streamline
  • Overdrive
  • 2, 4-D

Most effective control: Rosette stage during spring or fall.

Herbicides with good residual activity (e.g., Milestone, Opensight) appear to be the most effective over the long-term.

Adding 2, 4-D helps with burndown. Tank mixing, 2, 4-D, with Overdrive = very rapid burndown.

Bull Thistle
biennial
  • Milestone
  • Opensight
  • Escort XP
  • Transline
  • Garlon
  • Perspective
  • 2, 4-D
Same as musk thistle
Teasel
biennial
  • Milestone
  • Escort XP
  • Garlon
  • Roundup
  • Transline
  • 2, 4-D

Most effective control: Rosette stage during spring or fall.

For small populations, cut off seedheads, destroy and dispose properly.

Use a stout dose of herbicide and monitor. Teasel is tough; flowerheads and seed can be produced after treatment.

Poison Hemlock
biennial
  • Opensight
  • Telar
  • Roundup
  • 2, 4-D
Most effective control: Rosette through pre-bloom, early spring.
Leafy Spurge
perennial
  • Plateau
  • Banvel
  • Vanquish
  • Perspective
  • Roundup/2, 4-D

Most effective control: Spring or fall. Plateau works well and is most effective in the fall, just before frost.

Pull or respray plants that appear after treatment.

Use biocontrol for large infestations: flea beetles (Aphthona spp.).

Purple Loosestrife
perennial
  • Garlon 3A
  • Aquatic Roundup
  • Habitat
Most effective control: June to August.
Wild Parsnip
biennial
  • Escort
  • Opensight
  • 2, 4-D
Most effective control: Rosette stage.
Japanese Knotweed 
perennial
  • Habitat
  • Polaris
  • Arsenal Powerline
  • Roundup

Most effective control: Summer

Use a good surfactant, e.g., MSO with Arsenal, and Liberate with Habitat.

Sericea Lespedeza
perennial
  • Garlon
  • Escort XP
Can use either herbicide all summer. For best results use Garlon prior to branching (~July 4), and Escort in Aug. & Sept.
Russian Knapweed
perennial
  • Milestone
  • Perspective
Most effective control: Spring.
Garlic Mustard
biennial
  • Roundup
Spray rosettes in early spring (late Feb - early April) or late fall when little else is green to avoid non-target plants. Escort XP and Streamline may be effective, but due to residual activity should not be used where non-target species could be affected.

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.

  • Surfactants improve dispersion and reduce surface tension of spray droplets resulting in increased penetration. 
  • Crop oils and crop oil concentrates also improve dispersion and, by being oil, keep leaf surfaces moist longer than water allowing more time for penetration.
  • Stickers help prevent the solution from being washed off leaves.
  • Drift inhibitors control drift.
  • Antifoaming agents reduce foaming in the tank so it can be filled more easily.