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weed that looks like mimosa

Chamberbitter is a Tough Weed to Control (Harvey Cotten)

“Mimosa-like” weed has thousands of seeds hiding just under the leaf axils ready to spread in your garden.

Can you help me identify this weed that is growing in my lawn and in my flower beds? It has little yellow flowers and the leaves look like a small Mimosa tree. All of sudden it appears to be everywhere – what is it and how can I get rid of it? Thank you, Edward V.

Looks like the nasty little weed known as Chamberbitter (Phyllanthus urinaria) has found out where you live. Several years ago my landscape contractor friends in Birmingham were complaining about the prevalence of this weed and the difficulty they were having in controlling it. At that time I had not seen it as much in Huntsville but now it seems to be everywhere. I see it in a majority of the landscape beds at the Garden and have had several people send me samples and asking what it could be. Your description of it looking like a small Mimosa tree was spot on for that is what it looks like to me – a mimosa tree in miniature.

Chamberbitter is more of a tropical plant that loves hot weather and can tolerate drought conditions. It is a member of the Euphorbiaceae family and has the sticky, milky sap like many of the Spurge weeds that we deal with in the landscape. It has also been called Gripeweed, Little Mimosa and Leafflower as well as Niruri. This last common name is interesting in that in Spanish this means “to break stone” and in South America this plant (weed) has been used medicinally to treat kidney stones.

What makes Chamberbitter so difficult to control is multifaceted. First it is a very tough plant that grows fast, is drought tolerant, will flower and produce seed in just two weeks and the amount of seed it produces is abundant. Moreover, when the seed capsules explode they hurl seed in many directions away from the plant thus allowing it to spread over a larger area. Also, many of the more common pre-emergent herbicides we use in the spring are not effective on Chamberbitter and since it needs very warm soil to germinate, most of the early spring applications of pre-emergents are ineffective once May rolls around and Chamberbitter is germinating.

So how can we control this pesky little weed? First, by being very persistent in our efforts and then by taking a multi-prong approach. When I say multi-prong I am talking about implementing Mechanical controls, Cultural controls and lastly Chemical controls to help alleviate the problem. This is a very pervasive weed that can spread quickly so it will take all the tools at our disposal to get it under control.

If we start with Mechanical control it literally means pulling the weeds by hand or hoeing them out of the beds. Good news is that they will pull easily if the soil is wet but tend to break off if the soil is dry. Since they produce so much seed very quickly, I would not put these in your compost bin unless you know your pile will get hot enough to kill the seeds. This is a good way to get it under control if you are just seeing it for the first time.

When we look at Cultural controls it begins with proper mulching as a way to combat weed populations. The weed seeds need light to germinate so a good one to three inch layer of mulch over bare soil will help to keep weed seeds from germinating. However, if new weeds emerge from within the beds and then drop fresh seeds, they can grow on top of the mulch. Also if Chamberbitter is in turf areas then mowing regularly will keep weeds from setting flowers and thus seeds.

Lastly we look at Chemical controls and this involves the use of herbicides. With herbicides we have two classes of products to use. One is a Pre-emergent herbicide that is applied before we see the weeds growing and they work by keeping the weeds seeds from germinating. This is a great way to control weeds but timing is critical to insure success. The other type or class is a Post-emergent herbicide or one that we apply directly to the growing weed for control. Since Chamberbitter is so difficult to control we may have to use both types to get the weed population down to manageable levels.

Chamberbitter is considered a warm-season, broadleaf weed and thus grows during the hot dry summer season. However, unlike other warm-season weeds it does not germinate when the soil temperatures reach 52 degrees F, but waits until it is in the 70 degree range or until the month of May. For this reason, the standard application of pre-emergent herbicide most gardeners put out in mid-March is not effective in controlling Chamberbitter. It takes an additional application in May to work on this weed and it appears that only Isoxaben is effective. You can find this in Gallery or in products by Fert-i-Lome or Bayer Advanced.

When we look at Post-emergent sprays we really do not have a magic bullet to use for control. Even glyphosate (which kills everything it touches) has to be used several times to control. The best recommendation is using a product like Weed-B-Gon that has three different herbicides in combination to work on the weed. It will take several applications spaced 7-10 days apart to see a difference. One product by Bayer Advanced (Southern Season Long Weed Control for Lawns) has the three post-emergent herbicides plus the pre-emergent Isoxaben in combination. This can be applied with your garden hose and works great in turf areas.

I hope this helps – the easy part was identifying the weed – the hard part is getting rid of it.

Chamberbitter is a Tough Weed to Control (Harvey Cotten) “Mimosa-like” weed has thousands of seeds hiding just under the leaf axils ready to spread in your garden. Can you help me identify ]]>