Are Fall Herbicide Applications Effective on Perennial Invasive Plants?

Each year Techline receives questions from readers about treating broadleaf perennial weeds in the fall—including whether it is an effective application timing, what weeds are most susceptible to fall herbicide treatments and WHY? We interviewed seven weed scientists who work in natural areas about their research results and thoughts regarding fall application timing for perennial invasive plant control.

Weed Scientists Interviewed for “Ask the Experts”

Roger Becker, PhD, Extension Agronomist, Univ. of Minnesota. Joe DiTomaso, PhD, Extension Specialist,Univ. of California at Davis (retired). Stephen Enloe, PhD, Associate Professor, Univ. of Florida. Rodney Lym, PhD, Associate Dept. Head and Professor, North Dakota State Univ. Scott Nissen, PhD, Professor and Extension Specialist, Colorado State Univ. Timothy Prather, PhD, Professor, Univ. of Idaho. Mark Renz, PhD, Associate Professor and Extension Weed Specialist, Univ. of Wisconsin-Madison.

Roger Becker, PhD, Extension Agronomist, Univ. of Minnesota. Joe DiTomaso, PhD, Extension Specialist,Univ. of California at Davis (retired). Stephen Enloe, PhD, Associate Professor, Univ. of Florida. Rodney Lym, PhD, Associate Dept. Head and Professor, North Dakota State Univ. Scott Nissen, PhD, Professor and Extension Specialist, Colorado State Univ. Timothy Prather, PhD, Professor, Univ. of Idaho. Mark Renz, PhD, Associate Professor and Extension Weed Specialist, Univ. of Wisconsin-Madison.


Do you agree or disagree that fall is a good time to apply herbicides for perennial invasive plant control? 

Becker, DiTomaso, Enloe, Lym, Nissen, Prather, Renz: Fall applications can often provide equal or better weed control compared to spring or summer herbicide applications; however, success or failure will depend on: 1) the target weed species, 2) herbicide being applied, 3) growing conditions, and 4) soil residual properties of the herbicide.

Enloe: “It is important to define fall application timing. In the Southeast, early fall applications are often from two to six weeks prior to a frost when plants are still green and photosynthesizing. Herbicide application made immediately prior to or following a light frost on many cold-sensitive herbaceous plants may not be effective. This is different in the West where fall application timing is effective on many perennial plants following a light frost (26 to 30° F).”

DiTomaso: “For most perennial plants, particularly woody species, fall is an effective time for control. We found that for some species and herbicides (e.g. perennial pepperweed [Lepidium latifolium] treated with chlorsulfuron) both spring and fall applications give the same level of control.”

Lym: “You cannot make a general yes or no statement. For instance, glyphosate will not control leafy spurge (Euphorbia esula) when applied in June or July in our region (north central U.S.), but will give about 9 to 12 months of control when applied in September. Milestone^1 provides best control of Canada thistle (Cirsium arvense) at bud stage, but can work on rosettes in the fall. Absinth wormwood (Artemisia absinthium) is best controlled with either Milestone or Transline^2in spring (May), or in fall if you mow ahead of time.”

Prather: “Idaho has a number of perennial weeds where fall application timing is effective, such as rush skeletonweed (Chondrilla juncea) with Milestone; however, fall herbicide treatments do not provide optimum control of hawkweeds (Hieracium spp).”

Renz: “Research has shown that applications following the first light frost of the season (temperature drops below 32° F, but leaf tissue is not damaged) will provide a significant increase in control with several perennials. A hard frost with temperatures in the mid- to lower 20s (° F) may cause injury to some herbaceous perennials reducing control. Frost damage can take a day or more to show visually on plants. To assess potential damage to plants the morning after a suspected frost, gently squeeze the leaf with your thumb and forefinger, and release. If you see your fingerprint, this indicates the epidermis has separated and the plants likely have suffered frost damage to the point where we would not recommend spraying that fall.”


In your opinion, why does fall application timing work or not work?

DiTomaso and Enloe: Data are available on movement of total non-structural carbohydrates that demonstrates carbohydrate movement to roots in early to late fall, and depletion of reserves in early spring. The hypothesis is that systemic phloem-mobile herbicides^3 should move with carbohydrates and effectively control the root system of perennial plants. The question is…when are carbohydrates moving to important growing points? In herbaceous plants there is likely some variability, but in woody plants movement of carbohydrates in fall is more predictable.

Becker and Renz: Deposition of the herbicide close to plant crowns and root system appears to be important. Research suggests that the distance between the source (above ground leaves) and sink (crown buds and root) is a major factor in movement of photosynthates and presumably systemic herbicides. Buds on lateral roots or rhizomes are also very active metabolically in fall building up carbohydrate reserves to over-winter. In the upper Midwest, fall herbicide applications on herbaceous perennials (e.g. Canada thistle) that have been mowed and have fall regrowth are very effective. In unmanaged systems such as pastures or prairies that have not been mowed or grazed heavily, much of the plant material may be the shoots that originally emerged last spring with minimal new regrowth. As long as the lower portions of these original stems and leaves have green tissue, fall applications can be effective. 

Nissen: “Residual activity of the herbicide in soil is very important4. Root and/or root bud herbicide absorption from soil is a significant factor in fall and early winter, especially for weeds like Canada thistle and Russian knapweed. In Colorado, studies have shown that soil-residual herbicides (for example, Milestone) are absorbed by Canada thistle and Russian knapweed roots and/or root buds even when no top growth is present. In areas with high soil organic matter content (>3%), herbicide absorption by roots may be reduced. Although results from the upper Midwest indicate that above-ground green growth must be present to achieve good control, this is not the case in Colorado. Higher soil organic matter present in the upper Midwest may bind herbicides reducing root and bud uptake from soil in the fall.” 

Prather: “With fall applications you may get enhanced herbicide translocation in perennial weeds because of slower metabolic processes that detoxify the herbicide. Microbial degradation of soil-active herbicides would also be slower in fall allowing for a longer period of time for root uptake of the herbicide.” 

Becker, Lym and Renz discuss how dry conditions in late summer and fall can reduce effectiveness of fall herbicide applications. 

Becker: “In Minnesota and Iowa, the exception to better, more consistent control with fall applications has been in drought cycles where spring moisture was adequate, but by fall, the target weeds were severely moisture stressed and did not appear to translocate herbicides effectively. Rainfall totals and distribution start to transition rapidly moving from western Iowa and Minnesota into Nebraska and the Dakotas, increasing the likelihood of fall moisture stress and reduced control with fall vs. spring/early summer applications. The take home message – in the upper Midwest, assess the stress level of target weeds in the fall following abnormally dry periods. If plants are showing obvious moisture stress, you might be better off leaving a foliar herbicide in the jug.”

Lym: “This is not an easy question to answer. Herbicide efficacy in fall can be influenced by plant growth stage (e.g. Canada thistle mature stems vs rosettes), soil moisture, and canopy cover. If conditions are dry in fall, herbicide application may be ineffective.” 

Renz: “It appears that soil active herbicides such as Milestonemay improve perennial weed control in fall. Even a small percentage of the herbicide absorbed by roots in the fall, winter and early spring can improve perennial weed control. Moisture may also influence control. If summers are very dry and regrowth is limited (e.g. Canada thistle rosettes), then control may go from good to poor. A major reason for weed control failure in fall is no fall moisture.”


Which perennial invasive plants are good targets for fall herbicide application?

Following is a summary of some invasive plants that can be controlled with fall applications (listed by scientists in this interview). Herbicide options and rates are available at and in other online references.

Research on Herbicide Application Timing

  • Aulakh JS, SF Enloe, NJ Loewenstein, AJ Price, G Wehtje, and JH Miller. 2014. Pushing towards cogongrass patch eradication: The influence of herbicide treatment and application timing on cogongrass rhizome elimination. Invasive Plant Sci. and Mgt. 7:398-407.

  • Becker RL and RS Fawcett. Seasonal carbohydrate fluctuations in hemp dogbane (Apocynum cannabinum) crown roots. Weed Sci. 46 (3) pp 358-365.

  • Bukun B, TA Gaines, SJ Nissen, P Westra, G Brunk, DL Shaner, BB Sleugh, and VF Peterson. 2009. Absorption and translocation of clopyralid and aminopyralid in Canada Thistle (Cirsium arvense). Weed Sci. 57:10-15.

  • DiTomaso JM, GB Kyser, and EA Fredrickson. 2004.Control of black oak and tanoak in the Sierra Nevada range. Western Journal of Applied Forestry. 19(4):268-276. 

  • DiTomaso JM and GB Kyser. 2007. Control of Ailanthus altissima using stem herbicide application techniques. Arboriculture and Urban Forestry 33(1):55-63. 

  • DiTomaso JM, JJ Drewitz, and GB Kyser. 2008. Jubatagrass (Cortaderia jubata) control using chemical and mechanical methods. Invasive Plant Science and Management 1: 82-90. 

  • Doll J and M Renz. 2007. Multiflora rose. Ext. pub. Univ. WI-Madison.

  • Enloe SF, NJ Loewenstein, D Streett, and DK Lauer. Herbicide Treatment and Application Method Influence Root Sprouting in Chinese Tallowtree (Triadica sebifera). Invasive Plant Science and Management. (In press). 

  • Enloe SF and A Kniss. 2009. Influence of diflufenzopyr addition to picolinic acid herbicides for Russian knapweed (Acroptilon repens) control. Weed Technology 23:450-454.

  • Enloe SF and AK Kniss. 2009. Does a diflufenzopyr plus dicamba premix synergize Russian knapweed (Acroptilon repens) with auxinic herbicides? Invasive Plant Science and Management 2:318-323.

  • Enloe SF, GB Kyser, SA Dewey, VF Peterson, and JM DiTomaso. 2008. Russian knapweed (Acroptilon repens) control with low rates of aminopyralid in range and pasture. Invasive Plant Science and Management 1:385-389.

  • Enloe SF, RG Lym, R Wilson, P Westra, S Nissen, G Beck, M Moechnig, V Peterson, R Masters, and M Halstvedt. 2007. Canada thistle (Cirsium arvense) control with aminopyralid in range, pasture, and non-crop areas. Weed Technology 21:890-894.

  • Enloe SF, SJ Nissen, P Westra, SD Miller and PW Stahlman. 1999. Use of quinclorac plus 2,4-D for controlling field bindweed (Convolvulus arvensis) in fallow. Weed Technology 13:731-736. 

  • Enloe SF, A Osiecka and DK Lauer. 2011. Comparison of aminocyclopyrachlor to common herbicides for kudzu (Pueraria montana) management. Invasive Plant Science and Management 4:419-426. 

  • Kyser GB and JM DiTomaso. 2013. Effect of timing on chemical control of Dalmatian toadflax (Linaria dalmatica) in California. Invasive Plant Science and Management 6:362-370. 

  • Lym RG and TD Whitson. 1990. Chemical control of leafy spurge. pages 200-209. In: James, L.F., J.O. Evans, M.H. Ralphs, and R.D. Child (eds.) Noxious Range Weeds. Westview Press, Boulder, CO.

  • Lym RG and CG Messersmith. 1991. Correlation of environment and root carbohydrate content to picloram translocation in leafy spurge roots. J. Range Manage. 44 (3) p. 254-258.

  • Lym RG and CG Messersmith. 2013. Leafy spurge identification and control. North Dakota Extension Service. W-765-revised. Online 

  • Marsalis MA, LM Lauriault, SH Jones, and MJ Renz. 2008. Managing field bindweed in sorghum-wheat-fallow rotations. Online. Crop Management doi:10.1094/CM-2008-0818-01-RS.

  • Oneto SR, GB Kyser and JM DiTomaso. 2010. Efficacy of mechanical and herbicide control methods for Scotch broom (Cytisus scoparius) and cost analysis of chemical control options. Invasive Plant Science and Management 3:421-428. 

  • Prather T and J Wallace. 2010. Rush skeletonweed control with aminopyralid on Idaho rangeland. Western Soc. Weed Sci. Research Progress Report. P.22.

  • Prather T and J Wallace. 2011. Rush skeletonweed control with aminopyralid on Idaho rangeland. Western Soc. Weed Sci. Research Progress Report. p.25.

  • Renz MJ and JM DiTomaso. 2004. Mechanism for the enhanced effect of mowing followed by glyphosate application to resprouts of perennial pepperweed (Lepidium latifolium). Weed Science 52:14-23. 

  • Renz MJ. 2007. Fall management of thistles. Wisconsin Crop Manager 14(28):156.

  • Renz MJ. 2007. Fall alfalfa removal using herbicides. Wisconsin Crop Manager 14(98):160.

  • Renz MJ. Using herbicides to suppress cool season grass in Conservation Reserve Program fields in preparation for interseeding legumes. Univ. WI-Madison.

  • Renz MJ. Updated information on using herbicides to suppress smooth brome. Univ. WI-Madison. 

  • Wallace J and T Prather. 2011. Meadow hawkweed control at various timings using aminopyralid. Western Soc. Weed Sci. Research Prog. Rpt. Pp 6-7.

  • Wallace JM, TS Prather and LM Wilson. 2010. Plant Community Response to Integrated Management of Meadow Hawkweed (Hieracium caespitosum) in the Pacific Northwest. Invasive Plant Science and Management 2010 3:268–275.

  • Wilson RG and A Michiels. 2003. Fall herbicide treatments affect carbohydrate content in roots of Canada thistle (Cirsium arvense) and dandelion (Taraxacum officinale). Weed Science 51:299-304.

Published 2015; trademark updated June 2019.


^1 Milestone® herbicide

^2 Transline® herbicide

^3 Systemic herbicides are those that are absorbed by the roots or foliage and translocated (moved) throughout the plant. This includes herbicides Milestone®, Transline®, Tordon® 22K, Garlon® 4 Ultra, glyphosate, and many more.

^4 The length of time an herbicide remains active in soil is called soil persistence, or soil residual life. Herbicides such as Milestone, Tordon 22K and Transline have soil residual properties that allow for root and or bud absorption (uptake). Garlon 4 Ultra is not readily absorbed by roots. 

®™Trademark of Dow AgroSciences, DuPont or Pioneer and their affiliated companies or respective owners. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details. State restrictions on the sale and use of Milestone, Transline and Garlon 4 Ultra apply. Consult the label before purchase or use for full details. Tordon 22K is registered as a Restricted Use Pesticide. Always read and follow label directions.©2019 Corteva