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This is a continuation of a series started earlier this year in an attempt to warn homeowners about plants that come back to taunt. Earlier aspersions were cast on the tuberous sword fern (Nephrolepis cordifolia; see, edis.ifas.ufl.edu/AG120), a variety of blue porterweed (Stachytarpheta urticifolia: look for the native S. jamaicenensis which stays around 3 to 4 feet) and the sprawling Mexican petunia (Ruellia brittoniana).

Another cute little plant that fooled me, spreading dayflower (Commelina diffusa), is thriving in our recent cool weather. It supposedly like wet areas, but it seems very happy now in our drier conditions — and my irrigation isn’t even working!

This blue-flowering, viney plant is similar in form to the “wandering jew” and others in the Tradescantia genus that are commonly used for houseplants and hanging baskets up North. These plants are in the spiderwort family, Commelinaceae. They are monocots and thus, are more closely related to grasses than the dicots which they resemble with their broad leaves and pretty flowers.

My mistake was in allowing some of these twining plants to remain as fillers in some of my landscape beds. Before I knew it they were showing up in the yard — thickly, in the yard! The common broadleaf weed herbicide, Atrazine, didn’t slow the new outposts of spreading dayflower. Since it is a monocot, I tried a selective grass killer that can be sprayed over the top of broadleaf ornamentals without harm; however, there was also no harm to this weed.

Unfortunately, there is no selective herbicide that will kill this creeping dayflower. This is one green weed that even Roundup, amazingly, does not nuke. Sprays of Roundup (glyphosate is the common name of this herbicide) tend to make the stems brittle. When the vines break apart, they just reroot and the patch gets thicker than it was in the first place.

Dayflower requires diligent hand-pulling; don’t think twice, rip it out if you see it. Don’t walk by it and think that you’ll get it later. The herbicides that work best are those commonly available phenoxy combination broadleaf weed sprays that contain 2,4-D, dicamba and MSMA. These products cannot be used in ornamental beds without injuring other broadleaf ornamentals as well. (Note: Use of MSMA is also under investigation by state and local officials because it contains arsenic that may filter into drinking water and the Gulf of Mexico.)

Many of these products state that they are safe to use on St. Augustine grass lawns. I found that not to be the case, and even though we were still in our rainy season, my St. Augustine got fried along with the spreading dayflower. However, it seems that the dayflower is rebounding faster than the turf. Don’t let this weed on your property.

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Doug Caldwell is commercial landscape horticulture educator for the Collier County University of Florida Cooperative Extension Service. E-mail dlcaldwell@ifas.ufl.edu. Call 239-353-4244, x203. Extension service Web site: collier.ifas.ufl.edu