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What does it take to Control Invasive Plants?

by James P. Engel, © 2012

The book “Bringing Nature Home” by Douglas Tallamy makes the strongest and most convincing argument to date for the need to remove alien plants from our yards and natural area.  One of the main points  he details in his book, is the evolutionary relationship that developed between native plants and native herbivorous insects.  Insects are the primary converter of plant energy into animal energy that supports all the higher trophic levels in nature and native insects cannot survive and reproduce on alien plants. 

So you want to eliminate the invasive plants on your property?  Where do you begin? A flood of information is out there. Brochures, articles and web-sites abound but the target audience always seems to be the homeowner with a small lot and too much time on their hands. 

The first recommendations for control is nearly always for cultural methods: pulling, digging and cutting with hand tools. What are your options if you have several acres to treat, thousands of plants to control and limited time.  You certainly can’t pull your way out of your problem. Herbicides are only mentioned as a last resort and discussed in general terms for obvious reasons. Not enough information to give you any degree of confidence in using them.

Pulling and digging may only work on a few plant species and hand tools like loppers and hand saws can only be used on small woody stems. Hand tools are time consuming and take a lot of physical energy.  Most alien plants remain alive and continue to grow when only cut, so repeated cutting or use of another control method is nearly always necessary.

The lack of easy access to practical information creates an information barrier to anyone except the most determined individual. What is needed is useful , detailed information that would give someone enough information about what works, what doesn’t, what herbicides to use, rates, timing of application, equipment to use, and how to go about applying the material.

There is a great deal of knowledge that can only be learned from first hand experience. The only limitation in sharing this knowledge with others is that occasionally the information is geographically or species specific.

Anyone who has ever tackled a large invasive infestation knows that you have to match your tools to the size of the infestation. Some manual practices like pulling and digging will only be practical on a very small scale. Only by matching the control strategy with the size of your infestation will you be able to realistically tackle the problem and have a reasonable expectation of timely and effective control.

Even though it is quiet, uses no gasoline and still cuts the grass, nobody uses the old style rotary push mower anymore, its way too hard to push and takes far too much time. What if you only had a pair of loppers and a hand saw and were faced with a 20 acre wall of honeysuckle? Would you gladly take it on as a Herculean challenge or more pragmatically decide to tackle the New York Times crossword puzzle instead? . Any reasonable person wouldn’t choose to use tools and methods that takes longer, demand enormous amounts of energy and might not control the problem? When you are dealing with limited resources of time and money and an endless amount of invasive plants, it only makes sense that you would choose the method that gets the job done with the least amount of time and effort. Anything that restricts your efficiency means that fewer plants are treated and less land is cleared and nature loses in the end.

Knowledge is power and power will help motivate peopel to take action. People can learn from the experiences and mistakes of others so equiped with the experience of others they can begin tackling invasives with confidense.

The first hurdle is to estimate how long it will take.  As an example, lets say you have a 1 acre woodlot.  The entire woodlot is infested with common buckthorn.  They range in size from 1” up to 5 or 6” in diameter.  They are evenly distributed throughout the woodlot at an average spacing of 5 to 6 ft. Some will be further apart and some closer.  How do you estimate how many plants there are and how long it will take to cut and treat them all. You will need to make some estimates, without past experience to guide you.

Cut stump treatment is the most efficient method for eliminating buckthorn and any other shrub or tree with large woody stems.  This practice involves cutting the stem off at the ground level and then treating the cut surface with a herbicide to prevent resprouting from the stump and root system.  When you cut a stem you know the top part is dead and you are certain the herbicide will be absorbed into the plant from the cut surface.   This practice also uses the least amount of herbicide.

Two herbicides glyphosate and triclopyr are primarily used for cut/stump treatments and for foliar applications. These are active ingredient (AI) names that are used in products with different formulation names such as Round-up, Rodeo, Crossbow, and Garlon-4 so read the label carefully before buying. Cut/stump herbicides are normally diluted to a concentration of 10 to 15% AI. These active ingredients are also found in many over the counter homeowner products that can be found in garden centers.

A lightweight chain saw or better yet a forest clearing saw are the best tools to use for cutting woody stems.  Both are easy to operate.  A chainsaw will easily cut through small stem sfrom 1" diameter on up to the largest trunk you might tackle. A forest clearing saw will handle the smallest stems up to stems 6" in diameter. It takes only a little more time to cut through a large stem as it does a small one.   Small stems might take 1 to 2 seconds apiece to cut while larger stems will take a little longer say 4 to 6 seconds.  The average time for each stem will be 4 seconds. We estimate it will take 3 seconds to spray each cut surface with herbicide using a spray bottle.  We need to allow time to walk to the next stem and get ready to cut. Lets estimate 3 seconds per plant for moving from one to the next. Adding up the times and the total is 10 seconds per plant..  You have just calculated that it will take you 10 seconds to cut and treat one buckthorn plant. 

One acre of land covers an area 43,560 sq/ft in size or equivalent to a square 208.7 ft on a side. With buckthorn spaced 5 ft on center, each plant occupies 25 sq/ft in area.  Divide 43,560 by 25 to get 1742 plants per acre.

Our woodlot has 1742 buckthorn plants that take 10 seconds each to cut and treat.  Calculate the total time in seconds then divide that number by 60 to get the number of minutes.  The answer is 290 minutes or 4.8 hours. That isn’t a lot of time to spend per acre when you consider that the buckthorn may have taken 20 to 30 years to reach their current size and density. So spending 5 hours one time to reverse 30 years of invasive plants seems like a reasonable investment to protect your property from invasive plants.

From personal experience an infestation of buckthorn will take about 2 to 4 hours per acre.  What will vary from one site to another is the total number of stems, their size and where they are growing.  It takes less time to cut a few large stems than it does to cut many small stems. It also takes longer to cut plants growing in full sun with multiple stems and branches close to the ground, than it does plants growing in shade that have branch free trunks.  You will most likely have to do some follow up treatments in subsequent years to treat missed plants and any that might resprout. Total time should be no more than 1 to 2 hours.

What tools you use makes a big difference on how long it takes to cut stems and how much physical effort is involved.  A forest clearing saw is the most efficient tool you can use for cutting woody stem, next is a light weight chain saw. Each requires the least amount of effort compared to all other hand tools and both are fast and efficient.  Hand loppers require more physical exertion and work best with stems  1” in diameter or less. Hand saws can cut through larger stems than loppers but they are extremely slow and require a great deal of physical exertion.  They also are difficult to control and use close to the ground.  Branches frequently get in the way and the blade pinches and gets stuck. Weed wrenches  are long handled leverage tools designed to uproot whole plants along with their roots eliminating the need to use herbicides.  They’re limitations are similar to the other hand tools, much slower, more physical effort  to use and they are limited by stem size and stem shape. To calculate how long it will take you to do the same work using a hand saw versus a chain saw.  Time how long it takes you to cut a couple of stems, take an average time and then use the same formula you did for the chain saw.  If it takes you 20 seconds to cut a 2” stem and 90 seconds to cut through a 5 “ diameter stem, the average will be 55 seconds.

A spray bottle is an indispensable piece of equipment when doing cut/stump treatments. A spray bottle is far easier and faster to use than a paint brush and takes only one hand to use. You can repeatedly refill the spray bottle with herbicide that you purchase separately and dilute to the required concentration. Reuse a spray bottle that originally held herbicide.  The addition of a spray colorant to the herbicide solution lets you know what you have treated, the area covered and reduces the chance you will leave stumps untreated. Spray colorants such as Signal can be purchased from mail order nursery suppliers like Gemplers.

Cut/stump treatments can be done any time of the year except during the spring when the sap is flowing.  Systemic herbicides are least affective during spring when the plant is in its active growth phase.   Fall and winter are arguably the best time of year.  Most people have more free time at this time of year.  The plants have dropped their leaves so it is easier to see what you are doing and temperatures are cooler for working outside. I frequently work during the middle of winter with temperatures below freezing and haven’t noticed any difference in control. Herbicide mixtures can freeze in the spray bottle at this time of year.  Dilute the herbicide mixture with window washer fluid instead of water to prevent freezing.

What  to do with the brush after cutting? Leave it in place.  The brush will quickly decompose and return to the soil.  Brush can also be used to shelter native seedlings from deer or provide cover for wildlife.  Buckthorn in particular decays  very quickly, so save yourself some trouble and leave it in place.

Foliar sprays are the next most efficient treatment for large scale work. Foliar sprays can be used to control many species of invasive plants from shrubs to perennials. They are applied using a backpack sprayer or spray bottle for a few plants. It is effective in controlling smaller plants that cannot be efficiently cut with a chain saw or hand tools.  Foliar sprays are regularly used in old fields to treat small woody plants like honeysuckle, multiflora rose and small buckthorn or used to treat perennial invasives like Pale swallowwort and Japanese knotweed. Foliar sprays can take as little as 1 to 2 seconds per plant to treat.  More plants can be treated in less time than any other control method.  You can treat as fast as a person can walk, so large areas can be covered.  In an old field setting it can take longer to walk between plants than it does to treat.  The down side is that plants take longer to show symptoms and die. Plants may outgrow the treatment if coverage and dose is insufficient. Be careful about  overspray, spray drift may cause injury to surrounding plants.

To estimate the efficiency of spray treatments, lets estimate it takes 1 second to treat small  woody plants and three seconds to walk between each plant.  Using  the same density as the previous woodlot 1742 plants per acre, it will take 116 minutes to treat this one acre or 2 hours total.  The investment of only 2 hours at this early stage will prevent a much larger problem sometime in the future. 

Foliar sprays applied with a backpack sprayer work equally well in treating perennial invasive weeds.  Individual plants can be selectively spot treated and large masses of plants can be broadcast sprayed.

We all need to do our part to reclaim our wild lands from the ravages of alien plants.I will share some of my hands on experience working with a few alien plants that  I hope will get your own efforts started in controlling invasive plants.  

Oriental Bittersweet (Celastrus orbiculatus) Control using a combination of techniques. Use a chain saw and cut/stump treatments on large to small vines, loppers on medium to small vine. Trace vines back to their roots, cut close to the ground and treat cut surfaces with a herbicide summer through winter.  Seedlings and small vines can be pulled up by the roots.   Foliage can be treated in summer to fall with systemic herbicide with good results. Vines can be left to decompose inplace on the tree.  This strategy can also be used for Grape vine and other aggressive vines.

Pale Swallowwort (Vincetoxicum nigrum)  Herbicides are the only reliable means of control for large infestations.  Pulling, cutting and digging are impractical as the roots readily resprout.  Spot treat or broadcast spray from mid-summer to fall. Right at flowering is the ideal time to reduce seed production. Both glyphosate 2%AI and triclopyr  1 ½%AI  can be used with good control. Repeated applications for a couple of years will be necessary to treat new seedlings and resprouts.  The difference from year to year will be dramatic.  Swallowwort can be slow to show herbicide injury.  The first signs will be a drooping of the growing tips and wilting of leaves. Be patient the end is near.

Amur, Morrow, Tatarian honeysuckle ( Lonicera maackii, L. morrowii, L. tatarica.) Use a chain saw and cut/stump treatments on large plants.  Cut and treat any time of year even during the winter months. Honeysuckle produces numerous stems close to the ground that makes cutting challenging. Small bushes less than 3 ft, especially those growing in full sun are easier to treat with a foliar spray.  Honeysuckle, even large ones, respond quickly to foliar sprays.  Use triclopyr 2 to 4%AI in spring and early summer and glyphosate 2 to 5% in mid-summer to fall.  The higher rates will require less leaf coverage than the low rates for complete control.

Autumn olive (Elaeagnus umbellata) Cut/stump treatments can be used on all but the smallest plants. Treat all cut surfaces. AO is quite susceptible to foliar herbicide treatments.  Use same rates as honeysuckle. Triclopyr provides slightly better control than glyphosate.  Treat from mid-summer to fall.

Common Buckthorn (Rhamnus cathartica), Glossy buckthorn (R. frangula)  Use chain saw and cut/stump treatments on all stems larger than ½”.  Buckthorn wood is hard and difficult to cut with hand tools.  Cut and treat stems from summer through winter with high control. Buckthorn does not respond quickly to systemic foliar treatments. Only treat small plants or masses of seedlings with a foliar spray.  Use triclopyr in spring and summer and glyphosate in mid-summer to fall.

Barberry (Berberis sp.) , Privet (Ligustrum vulgare), Burning bush (Euonymus alatus) Use chain saw and cut/stump treatments on all large stems.  Seedlings are easy to pull by hand  and mid-size plants can be pulled using a shovel or mattock.  Foliar sprays can be used from summer through fall for large infestations. 

Recommendations  can be adapted for use on other invasive plants. 


this page updated January 20, 2012