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www.TallTimbers.org
September 2014 | Vol 7 | No 3   

 

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Invasive Grass Control in Upland Pine Forests

By Eric Staller, Natural Resources Coordinator

Bahia and Bermuda grass are invasive, exotic, sod forming grasses which develop into low-quality habitat for bobwhite and other wildlife. Due to past land management practices,  predominantly disking, mowing, chopping and thinning, sod forming grasses planted to hold roads have been able to invade the uplands jeopardizing the quality of ground cover. On many landscapes native grasses are preferred since they are the primary fuels carrying the frequent fires necessary to provide quality wildlife habitat. Therefore, the goal of recent research at Tall Timbers was to find the best methods to eliminate sod forming grasses from upland habitats.

The main focus of the research was to determine the best selective herbicide or combination of herbicides that specifically controls the problem sod-forming grasses and still allows the preferred native grasses and beneficial weeds to reestablish in the treated areas. In a perfect world we would like to mow or burn the area in the spring and then apply herbicide about a month later when the grass has re-sprouted and prior to seed head maturation to minimize the future seed source. However, in most established areas the seed source already exists so the application of herbicide can take place under the right conditions when time allows. The appropriate conditions for herbicide applications should occur when plants are actively growing and drought conditions should be avoided. Most importantly for applications to be fully effective apply a minimum of 30 minutes before a rain, this allows time for the herbicide to dry on the plant.

A total of 26 different treatments utilizing 8 different herbicides with multiple combinations, and concentrations were tested. Treatments were applied during June - August 2013, on three sites in Leon and Jefferson Counties in Florida. All treatment areas were surveyed using GPS, and photo points were taken prior to spraying, at 2-months post spraying, and at 1-year post application to determine efficacy of Bahia/Bermuda control and negative impacts on native grasses and forbs. All treatments were sprayed via a tractor and boom-less sprayer with 28-36 gal H2O and 21-32 oz non-ionic surfactant/acre. The common label for Sethoxydim is Poast®, and can be used; however Poast® has a higher percent active ingredient then the Sethoxydim SPC® we used, so the rates will be lower.

The following herbicide treatments showed the best one year control (>80% of target grass was killed): 

Bahia – The best herbicide/combinations included:

  •  Metsulfuron (Escort® @1.5-2oz/acre), or
  • Sethoxydim (Sethoxydim SPC® @24-34 oz/acre), or
  •  Metsulfuron + Aminopyralid  (Opensight® @1.6 – 3.5 oz/acre), or
  • Imazaquin (Septor 70 DG® @ 5oz/acre)

Adding Imazapic (3.2-13oz Plateau®) to any of these options increased Bahia control by inhibiting seed germination.

Bermuda – The best herbicide/combination included:

  • Sethoxydim (Sethoxydim SPC® @ 34 oz acre), or
  • Clethodim (Intensity 1® @ 44oz/acre), or
  • Adding Imazapic (3.2-13oz Plateau®) to any of these options will increase Bermuda control by inhibiting seed germination.

Bahia & Bermuda – The best herbicide/combinations included:

  • Sethoxydim SPC® @ 34oz/acre, or
  • Escort® @1.5-2oz/acre + Sethoxydim SPC® @24-34 oz/acre, or
  • 13oz Plateau®+2oz Escort®+44 oz Intensity 1®

The three herbicides that were NOT EFFECTIVE in controlling sod-forming grasses include:

  • Clethodim (Intensity 1® @ 15-36 oz/acre)
  • Imazaquin (Septer 70 DG® @ <3 oz/acre)
  • Metsulfuron (Escort® treatment containing < 1.3oz acre)

Bahia grass has a few more control options than Bermuda, and they all can be purchased without a pesticide applicators license. The selectivity was very similar between the successful Bahia treatments; virtually all the native grasses were retained while different treatments controlled a slightly different suite of forbs. 

Septor 70 DG® @ 5oz/acre, and  Opensight® @1.6-3 oz/acre worked well on Bahia, but also negatively affected many natives such as Goat’s rue (Tephrosia spicata), Sensitive briar (Mimosa quadrivalvis), and quality quail plants such as Lespedeza, Partridge pea (Cassia fasculata), Beggars lice (Desmodium sps), and Ragweed (Ambrosia artemisiifolia)

Sethoxydim SPC® @34 oz/acre had >90% control, and also controls nut grass, while not controlling the beggars lice, lespedeza, rag weed, partridge pea, Goat’s rue and sensitive briar.

An important lesson learned from this experiment is thorough inspection of a site is needed before herbicide application takes place; you need to identify your target species. Our experience at Tall Timbers suggests that Bermuda is often mixed in with the Bahia, and goes unnoticed until it is released. The recognition of both species of sod forming grass will be treated differently than if just one species existed.

Further testing will be conducted using different concentrations of Sethoxydim SPC®, and Sethoxydim SPC® + Plateau®, as that mixture suggests high control of both Bahia and Bermuda while minimizing impacts to important forbs. Imazapyr (Arsenal®) is a viable alternative to control Bahia and Bermuda, however, it is extremely hard on most grasses, and due to its soil activity cannot be sprayed under desirable hardwood species. Bermuda controllers include Sethoxydim SPC® @ 34oz/acre, and Clethodim @ 44oz/acre, which we tested, and Imazapyr and Fuazifop which we did not. Both Clethodim and Fuazifop do require an applicator license. While the 13oz Plateau®+2oz Escort®+44 oz Intensity 1® treatment did control >90% of Bahia and >80% Bermuda, it controlled too much of the beneficial vegetation leaving the ground barren and therefore is not a suggested control based on our goals.

Based on our current research and objectives at this time we recommend:

Bahia grass control - Sethoxydim SPC® @ 24-30 oz/acre or Metsulfuron @ 2-3.5oz/acre

Bermuda grass control - Sethoxydim SPC® @ 30-34 oz/acre 

To minimize germination - Plateau® @ 4-6oz/acre can be added to either chemical

Photo series of 6.5oz Plateau + 1.3oz Escort +23.4 Sethoxydim + 21 oz Phase II +36 gal H2O

 Pre-herbicide treatment

6/25/13 - Pre-herbicide application

Native grass clump

6/25/13 - A native grass clump surrounded by Bahia grass before herbicide treatments were applied.

Native grass

8/29/13 - the native warm season grass is growing while the Bahia grass is dying.

Bahia grass controlled

5/14/14 - Bahia is controlled, native grasses and forbs present.

Photos of 34oz Sethoxydim SPC +32 oz Phase II + 28 gal h2o

Bahia grass infestation

7/9/13 -  Bahia infestation, pretreatment

5/16/14 1-year post application, high quality ground cover

The mission of Tall Timbers Research Station & Land Conservancy is to foster exemplary land stewardship through research, conservation and education.