Annoying little weed with purple flower
What is this low growing weed in my Bermuda lawn? It has wiry stems, tiny purple aster-like flowers with a yellow center. It’s very invasive and, in spite of removing all by hand in August, it is back. How should we treat this?
Thank you for your help!
Denton County Texas
That is slender aster and it's an annoying weed. Unfortunately, nothing can be done to treat it at this time. It's mature, flowering and woody. Removing as much as you can by hand without it going to seed would help but is tedious. I've been pulling it up in my yard this fall.
In order to curb it, you will need to use a pre-emergent. I'll double check on the timing of that and get back to you.
Well, I asked Dr. Becky Bowling and she gave me a wealth of information!
Preemergence herbicides can be one part of a slender aster control program. Two important points: 1) Slender aster can perennate, so it does not always behave as an annual. This means that preemergence herbicides on their own are often not enough for total control depending on the severity of infestation. 2) Many of the preemergence herbicides commonly used in turf systems are not labeled for controlling slender aster. Best bet will probably be Gallery (Isoxaben). For a homeowner, there is Fertilome with Gallery. Unfortunately, isoxaben will not be effective on grassy annual weeds. This means that for total control, it will need to be combined with another product (Pendimethalin, prodiamine, dithiopyr, etc). Professionals can use Corteva's Crew product (isoxaben + dithiopyr) for a pre-mix option.
Regarding timing, we have already missed the window here in North Texas for this year. In general, I would say similar timing to when we would put out a fall preemergence herbicide for anything else: First wave of 70-degree soil temperatures (or less) for 4 or 5 consecutive days. We had an early cold snap this year - most winter weeds have already germinated, and slender aster is already blooming in my yard.
At this point, people should focus on spot-treating with standard broadleaf herbicides containing 2,4-D, dicamba, MCPP, etc. This includes products like RoundUp for Lawns, Weed B Gon. These herbicides can be very effective if used NOW to control the slender aster. As it matures, it develops a very deep taproot and becomes woody - making chemical control extremely difficult. Be aware that broadleaf herbicides (2,4-D, dicamba) can be damaging to St. Augustinegrass. Clients dealing with this in St. Augustine should pay VERY close attention to product labels to ensure they do not do accidental damage.
Many thanks to you and Dr. Bowling for your thorough response! I’ll get started on removing it by hand and use pre-emergent in the spring.