Maryland Grows

Eliminating unwanted plants is often one of the most challenging chores that gardeners face. Not introducing invasive plants is the fastest and most economical way to make a positive impact, as once invasive plants are introduced to your garden, it can take many years to eliminate these invaders from your landscape. 

Invasive plants propagate and spread by many different methods, which makes controlling them difficult and different for each species. Please learn feasible control tactics provided by land-grant universities or Extension factsheets/webpages before starting. Fact-based research is the absolute first step in getting ahead of plant invaders. Often invasive plants cannot be controlled 100% in just one growing season, but preventing the plant from making seeds or spreading is better than doing nothing at all.

Questions to guide your research: 

1. Get proper plant identification! Use Ask Extension, Local Extension Professionals, and Master Gardener Plant Clinics. Smartphone plant ID apps can give you some idea, but you should follow up and confirm the correct identification. Apps may be limited by photo quality and geographic area.
   1. Is the plant a woody perennial, herbaceous perennial, or annual? 
   2. Has the plant been a problem for several years in your landscape, or is it a relatively new concern? 
2. You must know how it is reproducing/spreading in your particular situation. For example, if the plant reproduces from stem/root cuttings, the last action you want to take is to mow/weed-eat/till the roots, which would cause the plant to produce hundreds of new plants.  
3. If controlling 100% is not a feasible option, determine how you can prevent the plants from spreading or allowing them to get stronger. 
4. If you have an invasive plant in your landscape and you really enjoy it, learn how to prevent it from spreading. For example, the spread of some plants can be prevented by removing flowers/viable seeds so that wildlife does not consume and spread them, or so that wind/rain does not blow away the seeds. 
5. Always include “MD Extension” with internet search engines to be sure that identification and control tactics specific to Maryland are being filtered to the top of your results.

Three basic control options are categorized below.

Mechanical control

Mechanical control options are often the first step that people take in controlling unwanted plants; however, these are by far the most physically demanding and often lead to a high level of site disturbance. Examples of mechanical control are:

1. Pulling  and digging.
2. Suffocation or smothering with landscape fabric, mulch, cardboard, multiple layers of newspaper, anything to block the sunlight and prevent the plant from growing.
3. Solarization: laying plastic over the plants to “cook” live plants and viable seeds with the heat that builds up underneath. 
4. Cutting, repeated cutting, or mowing in hopes of weakening stored nutrients so that the plants can not regenerate. This is also done to remove the flowering/seed structures. 

Biological control 

Biological control options utilize something else that is alive—insects, fungi, grazing livestock animals, etc. More and more of these options are being explored; however, sometimes the control agent may be 100% specific to the problem plant, or sometimes it may be able to feed on other plants too, which is the case with the Kudzu bug.  

Chemical control through herbicide application

1. Foliar Applications
2. Cut Stem or “Hack and Squirt” Treatments

Herbicides are a management tool that may be considered when other control measures have not been successful. Sometimes this control option provides the least amount of physical labor, low soil disturbance, and is more effective than other options. Pesticides can be overwhelming and intimidating, with misinformation and inaccurate “facts” being shared. If you would like to learn more about “mode of action” and how different herbicides are classified, check out this Herbicide Mode of Action link from Purdue.

A few questions that might help you determine if it’s time to explore herbicides as an option. 

1. Have you tried mechanical or physical control options without success? 
2. Would one application of herbicide save the soil on the site from being excavated, dug, or destroyed?  
3. Always use the most appropriate chemical control option by finding the plant that you want to control on the product label and following the application instructions carefully.
4. Remember, with any pesticide (herbicide, insecticide, fungicide, rodenticide, etc.), the Label is the LAW! This is true even with organic pesticides. 
5. The Environmental Protection Agency (EPA) is charged with approving, analyzing, and standing behind pesticides. Before approval, these herbicides are tested and labeled for use with specific instructions to minimize negative risk to yourself and the environment. Always use in accordance with the label and keep good records.
   1. Herbicides that are commercially available to purchase have been tested to know the recommended rates and residual activity in soils and on micro/macro organisms. There are a lot of unknowns with homemade solutions, so homemade “remedies” are not recommended.

Disposal of invasive plants

The last step in controlling invasive plants is proper disposal. Leftover plant materials can lead to potential accidental new infestations.

Proper disposal guidance: 

1. Burn– If your county/city allows the burning of yard debris, be sure to follow all safety regulations and restrictions and do not breathe the smoke.
2. Pile– Fully dead/dried woody material that does not have seeds/fruits and is not covered in soil (which could allow it to sprout roots) can provide great nesting and shelter sites for wildlife- Read “The Value of a Pile of Sticks in Your Yard or Landscape”. 
3. Dry or expose debris to intense heat– place debris in a black trash bag and let it “cook” for several weeks out in the hot sun, this will ensure that there are no viable seeds in the debris and all moisture is removed so that nothing can sprout. You can then add this to compost piles or dispose of it as you would “normal” landscape trimmings.
4. Check with your county/city government to find out if invasive plants should go in your yard waste or regular trash.

Let the particular plant that you are trying to control guide your management plan, and research the plant before you begin. Start control strategies on a small scale to see what works best and remember that many of the characteristics that led people to begin planting these invasives are the exact reasons that they are hard to control— some examples: wildlife resistance, good at spreading, breaking dormancy before natives early in the season. Also, keep in mind that many invasive species are a long-term fight and will require perseverance and, for best results, will require the use of different control tactics. 

Lastly, once you successfully control the problem species, have a clear plan of what you will do with this space in your landscape. Installing new plants or keeping the area mulched will help prevent soil erosion or new infestations of weeds. Here is a list of recommended native plants for Maryland. 

Additional resources: 

Removing Invasive Plants and Planting Natives in Maryland – University of Maryland Extension

(PDF) Managing Invasive Plants: Methods of Control – New England Wildflower Society

(PDF) Guidelines for Disposal of Terrestrial Invasive Plants – University of Connecticut

Everyone can help in the fight against invasive plants! Check the University of Maryland Extension website for an Introduction to Invasive Plants in Maryland and more information on how to reduce them. The absolute best way is to just never plant or introduce them into your landscape. 

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.