Chemical Control of Unwanted Vegetation

Woody plants often interfere with the productivity and utility of both agricultural and non-crop lands. Woody vegetation may reduce forage production in pastures, limit water movement in ditches, limit visibility along rights-of-ways, and interfere with people’s activities in others ways. Several management strategies are available to manage unwanted woody plants. No single strategy is appropriate for all situations. A basic understanding of the principles of woody vegetation control will help when designing an effective management plan.

Management methods: cultural, mechanical, and chemical

Cultural principles of suppressing vegetative weeds achieved by maintaining a highly competitive mix of desired species also apply to woody species. However, cultural practices alone may not be sufficient to prevent brush establishment in many situations. Nevertheless, efforts to maintain a dense, vigorously growing mix of desired forbs and grasses usually will reduce problems with woody vegetation. Grasses and forbs are excellent belowground competitors for soil moisture and rooting space and can limit woody vegetation to only the most competitive species.

Mechanical control measures vary in effectiveness from species to species. Oaks, maples, walnut, willow, black cherry, mulberry, honey locust, and box elder will usually resprout from the stump if the stump is left intact or untreated chemically. Ash, hickory, sycamore, alder, willow, and elm resprout readily when cut as young saplings or small trees, but they lose much of this resprouting potential as they age. As a general rule, sprouting is most vigorous in young deciduous trees before they reach their respective seed bearing years. Conifers will not resprout after cutting.

The season when trees are cut influences resprouting vigor. Food reserves stored in the roots are highest during the dormant season from November to early May and lowest just after the leaves are fully expanded in the late spring. The greatest degree of sprouting occurs when trees are cut while dormant and the least if they are cut after full leaf expansion. Cutting in the late summer may not give sprouts time to harden off before winter comes making them susceptible to winter injury and death.

Stump height also affects resprouting vigor. Taller stumps can sprout more because of higher food reserves in the remaining stem and because of more dormant buds beneath the bark on the stem, but sprouts higher up on the  stem develop poorer root structures and lead to weak soil attachment. Long term survival of trees developing from taller stump sprouts appears to be lower than if trees were cut at ground level.

Chemical control of woody vegetation is often very effective and economical. Herbicides often require less labor per acre to control woody plants than mechanical means. Frequently, mechanical and chemical means can  be integrated into successful control programs by treating the cut stumps to prevent resprouting or by cutting woody plants and spraying the regrowing foliage several weeks or months later.

There are three major considerations involved in chemical selection for control of vegetation:

  1. Identify the species of brush you are wanting to control. Many landowners may already be familiar with the tree and shrub types common to their area. However, if you don’t know, identification is not difficult. Our interactive identification key or the Iowa DNR page on forest invasive species can help you determine what plant you want to control. The product label can then be consulted to help select the right chemical for control of your woody plant problem.
  2. Identify the site classification. Application sites are classified as either cropland or non-cropland. Cropland is any land on which a crop is raised for the purpose of harvest or grazing. Cropland includes pastures and rangeland. Non-cropland is any land that is not pastured or cropped. Non- cropland includes fence rows, storage areas, industrial sites, around farm buildings, utilities, drainage ditch banks and right-of-ways such as pipelines, communications lines, electrical power lines, highways, and railroads. Product use should always be consistent with labeled uses. Products that are not labeled for pasture or rangeland use may, however, be used in areas where livestock grazing is anticipated if grazing restrictions specifically identified on the label are followed. The grazing restriction is the length of time livestock must be fenced out of the treated area before grazing can be resumed. When two or more products are combined, the longest grazing restriction must be followed.
  3. Select the preferred method of applying the chemical. The various methods of application are:
    • Foliage sprays: applied to stem and actively growing foliage
    • Basal spray: prepared by mixing chemicals in kerosene, diesel oil or bark penetrants and applied as a drench to the lower 18” of tree’s trunk or canes, thoroughly soaking the root crown around the stem
    • Cut stump: chemical applied to freshly cut stump surface
    • Frill or hack-n-squirt: chemical placed in frill made by overlapping ax-cuts around the base of the tree
    • Hatchet injection: chemical is injected into tree using a hypohatchet
    • Soil application: sprays, granules or pellets applied to soil surface or injected into the subsoil

Chemical Application Methods

man applying foliar spray chemical to shrub
Chemical control through foliar application.

Foliage spray applications should be made when leaves are fully expanded and the main spring sap flow has subsided (July - fall color change). Care must be taken to minimize drift of the herbicide from the target site. Low pressure, coarse (large water droplet) sprays, and drift reducing additives or equipment are recommended. Selective  herbicides  can  be  used  to  only  target  broadleaf  deciduous  trees  and  shrubs  which  leave  grasses unharmed. For multi-flora rose one of the best times to use a foliar spray is just after peak bloom in the early summer. Just after the white blooms fall off the plant is at its weakest point and a foliar spray with a product such as Crossbow is highly effective. Within days you will be able to see what has “take” and what you missed with  the first spray.

man applying chemical basal bark spray to the base of a small tree
Basal bark spray should saturate the lower 18 inches of the trunk, crown buds, exposed roots, and soil directly around the base of the tree or brush. 

Basal sprays are very effective on resprouting species and can be used to kill cane patches and thickets, as well as large trees up to 6-8 inches in diameter. Oil soluble herbicides are applied in a bark penetrant, diesel oil, or kerosene carrier. The spray should saturate the lower 18 inches of trunk, crown buds, exposed roots and the soil directly around the base of the trees or brush to optimize control. Applications can be made any time of year, although fall and dormant season treatments often are most effective. Due to the high cost of diesel oil, which is used as the herbicide carrier, products have been developed that allow water to be used as a portion of the carrier liquid. Most vegetative ground cover will be killed by chemicals applied in a diesel oil carrier. Do not use if there are desirable species close by. Carefully read the label if you are working near bodies of water.

application of dyed chemical to a cut stump
Cut stump treated with chemical and dyed blue to ensure all stumps are treated. 

Cut-stump, Girdle, Frill – “Hack-n-Squirt”, and Hatchet injection methods are very effective on resprouting species of  any size. Treatment can be made any time of year. However, application made during periods of heavy sap flow in spring may result in poor control or injury to surrounding trees. These treatments are excellent for selectively controlling unwanted trees and thick stemmed brush without injury to surrounding trees, bushes, and ground cover. However, brushy thickets, canes, and multi-trunk trees are difficult to treat. Treat the plant before the cut surface dries (within 2 to 3 hours after cutting but preferably within 15-30 minutes) for optimum control. Only the outer edge (sapwood-cambium area) needs to be treated. Several products are formulated specifically for cut- surface treatments (Tordon RTU, Weedone CB, Banvel CST). These products usually contain penetrants and  dyes, and do not require mixing. A common error when using any of these three methods involves over- application of chemical. This wastes the chemical which can be expensive and it can lead to flashback in the soil. Flashback is where the chemical enters the soil around the tree or shrub that you were intending to kill and it kills all plant material in that zone. Some chemicals can sterilize the soil for years and not allow desired trees to establish and grow. Glyphosate “Roundup” has been shown to be equally effective in cut stump, frill, and hatchet injections by varying the concentration. A 50/50 mix of Glyphosate/water is highly effective from August- November and from November –February a 75/25 roundup /water and even a 100% glyphosate spray will control trees. Soil treatments include pellets, beads, granules, and liquids. The herbicide moves through the soil to the root zone and then is translocated upward  in the vascular structure of the plant to kill the above and belowground portions of the plant. Treatments are applied within the drip-line of target plants. Any sensitive nearby trees that root into the treated area will be injured or killed. Soil-applied herbicides usually remain active in the soil for several months; these chemical may be applied any time of the year except when the ground is frozen.

The tables below provide basic information on several products registered for controlling woody plants and the approved application sites and methods of application for herbicides registered for brush control. Before using any product, read the current label to insure that the product is used appropriately. No endorsement of products or firms in intended, nor is criticism implied of those not included.

Chemical Treatment According to Species

Species

Chemical Options Treatment Delivery Options
Autumn Olive

2% Garlon 4 Ultra

2 oz. Escort XP

Foliar (when growing)

20% Garlon 4 Ultura + Bark Oil Basal Bark and Cut Stump (Mid-summer - late fall)
Black Locust

5% Transline with water

Cut Stump (Mid-summer - late fall)
5% Transline 2. Basal Oil Basal Bark (Mid-summer - late fall)
16 oz. Transline

Girdling (Mid-summer - late fall)

7 oz. Milestone VM

10% Milestone VM with water for cut surface 

Hack-n-Squirt, cut stump (Mid-summer - late fall)
Boxelder

20% Garlon 4 ultrs + Bark Oil

Basal Bark or cut stump (Mid-summer - late fall)
2% Garlon 4 Foliar when growing
Buckthorn 20% Garlon 4 Ultra + Bark Oil Basal Bark (Mid-summer - late fall)
Pathfinder II (RTU) Cut stump (Mid-summer - late fall)
2% Garlon 4 Ultra, spray to thoroughly wet Foliar (when growing)
Chinese/Siberian Elm 7 oz. Milestone VM  
1.5 oz Escort XP
Eastern Redcedar Chemicals are normally not used - mechanical means of girdling below the lowest branch, mowing, and prescribed fire will all remove red cedar
Multiflora Rose

3.3 oz. Opensight

1 oz. Escort IP or 1 gram/gal

2% Garlon 4 ultra

3% Crossbow at flowering

Foliar (when growing)
6-12% Stalker + Oil Basal Bark (year round)
Poison Ivy 1-2% Garlon 4 Ultra  
Prickly Ash 

20% Garlon 4 Ultra + Bark Oil

Basal Bark and Cut Stump (Mid-summer - late fall)

2% Garlon 4 Ultra

1.5 oz. Escort XP per 50 gal. water

Foliar (when growing)
Reed Canary Grass

12 oz. Plateau

2 oz. Oust XP

32 oz. Journey

48 oz. Habitat

1% Intensity

10% Accord XRT II + 0.5-2 oz. Oust XP late season

All mixes should include TACTIC surfactant

 
Garlic Mustard

2-3% Garlon 4 Ultra

3% Accord XRT II

1 oz. Oust XP

Foliar (early spring when growing)
Honey Locust 20% Garlon 4 Ultra + Bark Oil Basal Bark (Mid-summer - late fall)
Pathfinder II (RTU) Cut Stump (Mid-summer - late fall)
2% Grazon P+D Foliar spray (when growing)
Honeysuckle

2 oz. Escort XP

5% Accord XRT II

Foliar (when growing)
20% Glyphosate Cut Stump (year round)
15% Garlon 4 Ultura + Oil Cut Stump (year round) Basal Bark (fall)
Ironwood 20% Garlon 4 Ultra + Bark Oil Basal Bark (Mid-summer - late fall)
Pathfinder II (RTU) Cut Stump (Mid-summer - late fall)
2% Garlon 4 Ultra Foliar spray for resprouts
Japanese Barberry

2-3% Garlon 4 Ultra

2 oz. Escort XP

Foliar (when growing)
Japanese Knotweed

1% Arsenal or Habitat

0.5 oz. Milestone VM/gal

Cut twice in the growing season and spray foliar regrowth in fall
Sumac Tordon RTU Cut Stump

2% Garlon 4 Ultra

7 oz. Milestone VM per 50 gal. water

Foliar (when growing)

 

Approved Application Sites and Methods of Application for Herbicides Registered for Brush Control

Chemical Product Active Ingredient Approved Sites Application Method Residual Activity1
Pasture Ditch Banks Foliar-Stem Spray Cut-Surface Basal Bark Soil

2, 4-D

2, 4-D

Yes

Yes

Yes

Yes

Esters

No

1-2 weeks

Access

Picloram + triclopyr

No

No

No

No

Yes

No

1 year

Arsenal

Imazapyr

No

Yes

Yes

Yes

No

No

1-2 years

Banvel, Vanquish

Dicamba

Yes

Yes

Yes

Yes

No

No

2-6 weeks

Chopper

Imazapyr

No

Yes

No

Yes

Yes

No

1-2 years

Chopper RTU

Imazapyr

No

Yes

No

Yes

Yes

No

1-2 years

Contain

Imazapyr

No

Yes

Yes

No

No

Yes

1-2 years

Crossbow

Triclopyr + 2, 4-D

No

Yes

Yes

No

Yes

No

2-3

months

Escort, Ally

Metsulfuron methyl

Yes2

Yes

Yes

No

No

Yes

1 year

Garlon

Triclopyr

No

Yes

Yes

Yes

Yes

No

2-3 year

Hyvar

Bromacil

No

Yes

No

No

No

Yes

1 year

Kernite

Fosamine

No

Yes

Yes

No

No

No

1 year

Pathfinder II

Triclopyr

No

Yes

No

No

No

No

2-3

months

Pathway

2, 4-D +

picloram

No

No

No

Yes

No

No

1 year

Round Up Pro

Glyphosate

Yes

Yes

Yes

Yes

No

No

None

Spike

Tebuthiuron

Yes

No

No

No

No

Yes

1-2 years

Tordon 101

Picloram + 2, 4-D

No

No

Yes

Yes

No

Yes

1 year

Tordon K

Picloram + 2, 4-D

No

No

Yes

Yes

No

Yes

1 year

Velpar

Hexazinone

No

No

Yes

No

No

Yes

3-6

months

Weedone 170

Diclorprop

+ 2, 4-D

No

Yes

Yes

Yes

Yes

No

2-4 weeks

Residual Activity is dependent upon rate applied and environmental conditions

Only Ally may be used for pasture


This article is a web-based modification of the original publication "F-341 Chemical Control of Unwanted Shrub and Tree Vegetation" written, revised, and edited by Jesse A. Randal, former Iowa State University Extension Forester.