Cogongrass (Imperata cylindrica) is one of the greatest invasive plant threats in Alabama and the southeastern United States. Although it has been here for more than a centurythe problem has dramatically increased in the past few decades.

Many land managers actively and aggressively manage cogongrass. Auburn University researchers have worked on solutions for cogongrass for many years. This publication provides a summary of that research and is in the form of answers to the most common questions regarding cogongrass management.

Q: Can I hand pull cogongrass?

Cogongrass has sharp leaf edges and razor-sharp sprouts at ground levelmaking hand pulling quite hazardous. Furthermoreit is extremely difficult to pull cogongrass without leaving behind rhizomes (underground stems)making this approach largely ineffectiveeven for very small patches.

Q: Will tillage alone control cogongrass?

In areas that can be accessed with machineryrepeated tillage that breaks up the entire rhizome layer will eventually exhaust the energy reserves of cogongrass rhizomes. Tillage fragments the rhizome networkincreasing new shoot emergence. When repeated after new shoot emergencetillage will further disrupt growth and decrease stored energy reserves. This approach of repeated tillage can work well over time if repeated frequently. If tillage is not repeatedthe cogongrass patch may end up thicker than it was to start with and can scatter rhizomes into areas not previously infested. Shallow or infrequent tillagesuch as diskingfield cultivatingor chisel plowingwill generally not control cogongrass. Research has shown rotary tillers powered by tractor PTO are the most effective when used repeatedly to prevent new emergence. Clean tillage equipment carefully to avoid spreading rhizomes.

Q: Will prescribed fire control cogongrass?

No. Prescribed fire at any time promotes cogongrass to the detriment of almost all other species. Dense cogongrass can burn hot enough to kill many fire-tolerant specieseven young loblolly and longleaf pine. Burning dense patches of cogongrass when trees are at risk is not recommended. Cogongrass can also be spread by fire plows that can drag rhizome pieces to uninfested areas.

Q: Will grazing control cogongrass?

Cogongrass was tested as a potential forage crop in Mississippi and Florida more than 80 years ago and was virtually useless. Livestock will graze very young cogongrass shootsbut they tend to avoid it as it matures. Mature cogongrass foliage is high in silica and low in forage quality. Some cattle producers have used mowing to stimulate new growth for cattle grazingbut this is not an effective control strategy.

Q: What is the best herbicide to treat cogongrass?

Two herbicidesglyphosate and imazapyrare most effective for cogongrass management. Howeverthey are generally situation specific and require multiple treatments for complete control. Glyphosate is the safest option when treating cogongrass around desirable treesshrubsor other vegetation but is less effective than imazapyr. Imazapyr is more effective than glyphosate but cannot be used near most desirable vegetationunless severe injury or death of that vegetation can be tolerated. Some pinesincluding loblolly pineare tolerant of imazapyr. Longleaf pinehoweveris not tolerant of rates of imazapyr needed to control cogongrass. Since imazapyr is absorbed by plant roots in addition to foliage and root locations cannot be seenunintended consequences can result.

Q: Do any other herbicides provide effective cogongrass control?

Glufosinate (FinaleCheetahInterline) will provide a rapid brownout of the foliage. Howeverit does not translocate into the rhizomes and does not provide long-term control. Aminocyclopyrachlor combined with reduced rates of imazapyr has been used in noncrop areas and rights-of-way to suppress cogongrass in an attempt to reduce injury to desirable sods. Howeverour data indicates it is not effective as a stand-alone treatment for long-term control.

Q: What rate of these herbicides should I use?

For any herbicideuse rates should be in accordance with label rates for the specific product you select. For glyphosate formulations that contain 41 percent active ingredient (4.0 lb./gal.)a 4 to 7 percent solution is recommended for spot treatmentsand broadcast treatment rates should generally be between 3 and 5 quarts per acre. For glyphosate formulations that contain 54 percent active ingredient (5.4 lb./gal.)a 3.5 to 6 percent solution is recommended for spot treatmentsand broadcast treatment rates should generally be at 7 pt per acre. For imazapyr formulations that contain 27.7 percent active ingredient (2 lb./gal.)a 2 percent solution is recommended for spot treatmentsand broadcast treatment rates should generally be between 48 and 64 fluid ounces per acre. For imazapyr formulations that contain 53.1 percent active ingredient (4 lb./gal.)a 1 percent solution is recommended for spot treatmentsand broadcast treatment rates should generally be between 24 and 32 fluid ounces per acre. When using herbicidesalways read and follow the label.

Q: Should I tank mix glyphosate and imazapyr?

There is no antagonism between glyphosate and imazapyr; they can be tank mixed. There may be some benefit to mixing the two herbicides if lower imazapyr rates are used. Howeverat the rates recommended aboveresearch has not shown a control benefit in mixing the two herbicides. Tank-mixing herbicides such as these with different modes of action may be useful to prevent herbicide resistance. Mixing glyphosate with imazapyr does increase the speed of visual symptoms on treated cogongrass foliage compared to using imazapyr aloneas symptoms from imazapyr treatments can take as long as 30 days to become visible.

Q: What is the best herbicide application timing?

A single application of either glyphosate or imazapyr will rarelyif evercompletely eliminate the entire rhizome layer at any timing. Howeverthe optimal treatment window for both herbicides is late summer through early fall. If spraying in the fallit is important to spray early enough to give the treatment time to work (approximately 4 to 6 weeks) before a killing frost.

Q: Can I treat in the early spring to prevent cogongrass flowering and seed production?

Early spring treatment of the first green cogongrass shoots generally provides inconsistent reduction of flowering. Howeverfall treatment has worked very well to prevent flowering the following spring.

Q: Should I add surfactant to the tank?

For glyphosatesome products already contain surfactant and do not need extra. Add a nonionic surfactant at 0.25 to 0.5 percent v/vif the label recommends it. If water hardness is an issueadding ammonium sulfate to the spray tank is recommended when using glyphosate. For imazapyradd a nonionic surfactant at 0.25 percent v/v or methylated seed oil at 1 percent v/vdepending on the herbicide formulation used.

Q: Should I add a dye or spray indicator?

A blue spray indicator is useful when spot spraying small cogongrass patches and is generally easier to see on the treated foliage than other colorssuch as red. Spray indicators are easy to work withwater solubleand do not stain like some true dyes.

Q: Should I mow or burn to remove the thatch layer before treatment?

For summer or fall treatmentsthe answer is no. For spring treatmentsremoving the old growth may stimulate new cogongrass growth and result in more leaf area at the time of treatment. Howeveras previously discussedburning cogongrass at any time may injure or kill many trees. Mowing or burning in the winter may stimulate flowering in the spring. In additionmowing cogongrass may result in a thatch layer that prevents the deposition of spray solution onto cogongrass foliage.

Q: How much regrowth do I need to spray after mowing or burning?

Allow at least 12 to 18 inches of regrowth before treating. If you treat with less regrowthcontrol may be poor. It is also fine to allow more than 18 inches of regrowth.

Q: Should I spray beyond the edge of the patch?

Cogongrass spreads laterally by creeping rhizomes. You can often find a few small shoots creeping beyond the patch edge into numerous vegetation types. Some applicators have reported the formation of cogongrass halos (also called doughnuts) around patches in the growing season after treatment. This has prompted some applicators to spray a band about 10 feet wide beyond the patch edge. This is not recommended if you are using glyphosate because it has no soil activity. This is a useful option if you are using imazapyr because it may provide several months of soil activity. Quickly digging out beyond the patch edge will help you determine the prevalence of rhizomes beyond the patch edge.

Q: Can I treat cogongrass growing along water?

Yesbut only if you use a formulation of glyphosate or imazapyr labeled for use in aquatic sitesand always follow the label directions. DO NOT use any glyphosate product not labeled for aquatic use as it contains a surfactant that is toxic to aquatic organisms.

Q: How many times will I have to spray to completely eliminate all the rhizomes?

Research at Auburn has shown that imazapyr applied once per year for 2 or 3 years can eliminate the entire rhizome layer. Glyphosate applied twice per year in the late spring and fall for 2 or 3 years can also completely eliminate the rhizome layer. Significant differences have also been observed between cogongrass patches in the time it takes to eliminate the rhizome layer completely. Many land managers have noted this. The size of the cogongrass patchthe density of rhizomesand other site conditions may impact treatment success.

Q: Are there any cost-share programs available to help with cogongrass treatment?

The National Resource Conservation Service (NRCS) has offeredat timesassistance for cogongrass treatment through the Environmental Quality Incentive Program (EQIP) or other programsso check with your local office. The Alabama Forestry Commission occasionally has funding to assist with cogongrass control.

Revised by Nancy LoewensteinExtension SpecialistForestry and Wildlife SciencesAuburn University. Originally written by Stephen Enloeformer Extension Weed Specialistand Nancy LoewensteinExtension SpecialistForestry and Wildlife Sciencesboth with Auburn University

Revised August 2023Cogongrass Management FAQANR-2230