Notes on Herbicides

All of the herbicides listed below are mobile within the plant. These types of herbicides can be taken up by plant roots and/or foliage and moved throughout plant tissues. For the most part, these herbicides accumulate in meristematic tissues or growing points of the plants. They will often follow the flow of sugars within the plant; in perennials moving up in the spring months to feed new foliar growth, moving downward in the fall months for storage in the roots/rhizomes.

Regarding application techniques for herbicides (foliar, basal bark, cut-stump), please follow guidelines in the “Herbicide Application Techniques for Woody Plant Control” (UF-IFAS Pub. SS-AGR-260) document following this section.

AMINOPYRALID (MILESTONE) – This herbicide controls plants by disrupting the normal hormone balance. Specifically this herbicide targets auxins, causing uncontrolled growth in susceptible plants. Aminopyralid can be applied to plant foliage, where it is readily taken up by the leaves. This product will also persist in the soil and absorbed by plant roots. Because of this activity, aminopyralid is very effective in controlling seedlings that may germinate after an initial treatment. In general, aminopyralid is effective only on certain broadleaf species and is safe on grasses.

GLYPHOSATE (ROUNDUP, OTHERS) – Glyphosate is probably the most common herbicide that can be used for invasive plant management. Glyphosate blocks the formation of essential plant amino acids, which are building blocks of proteins and enzymes. Glyphosate is generally applied to plant foliage and is considered to be a non-selective. However, many woody species are not completely controlled by glyphosate and often regrow. Glyphosate does not possess soil activity and therefore does not provide residual control.

TRICLOPYR (GARLON 3A, GARLON 4) – Triclopyr is widely used herbicide for invasive plant control, primarily woody brush and trees. Triclopyr has little to no activity on grassy weeds. This herbicide controls plants by disrupting the normal hormone balance. Specifically this herbicide targets auxins, causing uncontrolled growth in susceptible plants. At rates used in most situations, triclopyr does not possess soil activity. Garlon 3A is formulated as a salt, with 3 lbs of active ingredient per gallon. This formulation is less volatile than Garlon 4, but does not penetrate as effectively and therefore is not as effective as Garlon 4 at comparable rates. Garlon 4 is formulated as an ester with 4 lbs of active ingredient per gallon and has greater volatility. This formulation should not be used where there is a significant potential for off-target spray drift.

IMAZPAYR (ARSENAL, CHOPPER, STALKER, HABITAT, ETC.) – Imazapyr is also widely used for invasive plant control and has excellent activity on grasses. This herbicide blocks the formation of essential plant amino acids, which are building blocks of proteins and enzymes. However, imazapyr blocks a different set of amino acids as compared to glyphosate. Imazapyr can be applied and taken up by plant foliage, but also possesses a good deal of soil residual activity. This often provides superior control, due to continuous uptake of the herbicide through the root system. However, this residual activity can cause problems with carryover to desirable species.

METSULFURON (ESCORT) – Metsulfuron can be used for certain invasive species, although there has been limited testing of this product on the wide range of invasive plants. Metsulfuron acts in the same manner as imazapyr, blocking the formation of essential amino acids which then are used to make proteins and enzymes. Metsulfuron is applied to the foliage, although this herbicide does have some residual activity. However, the residual activity is not to the extent of imazapyr.

Helpful Notes:

  1. Surfactant – 0.25% is the standard rate for foliar herbicide applications, 2 teaspoons per gallon.
  2. Dry time – generally 4-6 hours is adequate, but the longer the better for glyphosate
  3. Pay particular attention to herbicide labels near wetlands or bodies of water.
  4. Vines – if the vine can be pulled to the ground and sprayed, more herbicide may be absorbed by the plant and significantly better control is generally observed. Due to logistics, this method can only be used in limited areas.

The use of trade names in these publications is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.

Excerpted from the University of Florida, IFAS Extension, Circular 1529, Invasive Species Management Plans for Florida, 2008 by:

Greg MacDonald, Associate Professor Jay Ferrell, Assistant Professor and Extension Weed Specialist
Brent Sellers, Assistant Professor and Extension Weed Specialist
Ken Langeland, Professor and Extension Weed Specialist Agronomy Department, Gainesville and Range Cattle REC, Ona
Tina Duperron-Bond, DPM – Osceola County
Eileen Ketterer-Guest, former Graduate Research Assistant

 

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