One of the biggest challenges when managing invasive species is controlling the population before it goes to seed. Most invasive plants have hundreds or thousands of seeds each and once it releases them it exponentially increases the effort needed to control the population. This is especially important in newly established populations. Each viable seed that is allowed to enter the ground represents a potential new plant which will in turn produce seed unless stopped, therefore early management is key to reducing the spread and maintaining natural environments.
Although control methods and timing can vary slightly by species and geographic location, it’s generally best to either spray or cut invasive species in the early spring (March or April). This reduces negative impacts on desirable species while also ensuring the species is controlled before seed can be produced. Sometimes early spring control is simply not possible – maybe you weren’t able to identify it early on, missed a certain area, or were simply busy – that doesn’t mean all is lost. One possible method of slowing down invasion is to cut the seed head off, bag it up, and throw it away.
Before we start talking about how to control plants with mature seed heads it is important to understand what they are and how to recognize them on a plant. We are exposed to seeds regularly in daily life, but some seeds might not look how you would expect. It is easy to recognize sunflower seeds, bird seeds, or the seeds inside tomatoes, cucumbers, pumpkins, etc., but take a look at these pictures to test if you would recognize where seeds are stored on these invasive plants.
Many herbaceous invasive plants produce their seeds in the late summer, making it ineffective to spray or mow which might spread the seeds even further, but that doesn’t mean that we can’t still manage them. The best way to keep seeds from spreading in late summer on many herbaceous invasive species is to cut off its seed head or flowers. Unfortunately, this isn’t always practical or safe. When dealing with large populations or monocultures it is often easiest to simply spray the plant with herbicide until numbers are significantly reduced. As always, herbicide should be applied in accordance with the label using appropriate chemical application methods as outlined by Purdue Extension.In some cases – such as with Poison Hemlock - it is unsafe to cut the seeds off of a plant due to its toxic nature. For a more complete management guide regarding poison hemlock, please use this link from the Dubois County SWCD.
When cutting the seeds off a plant, immediately put it into a yard waste bag without walking around or shaking the seed off of the plant (this will spread the seed). Additionally, it is smart to use shears, trimmers, or a knife which is sharp to minimize shaking the plant. It’ is important to make sure that the bag is tied shut and there aren’t any holes or tears in the bag so that seed can’t escape and spread further. If your bag gets a hole in it or tears simply double bag it before disposal.
It’s important to remember that cutting seed heads off won’t kill the plant, but it does help to significantly reduce how fast it spreads to buy time until next growing season. A good practice after cutting seed heads is to spray the plant with an appropriate herbicide, this will kill the existing plant, opening up space for natives to colonize the area. After you have cut off the seed head and sprayed, cut, or mowed the plant to kill the plant you will need to keep an eye out for any new sprouts or missed seed heads and treat those accordingly.
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