American Burnweed escapes preemergent herbicide control
Question from Steve Schmidt, Virginia Green Lawn Care, Inc., Williamsburg office: A client is complaining that our preemergence herbicide treatment failed this past season on the basis of the presence of burnweed on his sports fields. The site did not have any crabgrass this past summer, so I believe the pre-emergence worked.
Another issue I believe that helped the burnweed in spring 2016 was mowing was very sporadic because of all the rain. The client could not mow for 2-3 weeks at a time. From my experience the more one can mow will help control the weed until the Bermuda grass starts to grow more consistently.
I guess I am looking to justify that what we sprayed did work but with burnweed one would have to spray later with POST broadleaf control, say mid spring. I have done some research online and the summary I get is that the burnweed will germinate in the thatch layer above the pre-emergence.
Dr. Mike Goatley responds: This is a common occurrence with American burnweed, Steven. This weed seems to be on the increase each year. It is in the Asteraceae family and produces ‘parachute seed’ that are easily wind dispersed (and causes the seed to remain on top of the soil/turf canopy surface, negating most PRE herbicide control). This weed is also often called ‘fireweed’ and is one of the first weeds to appear in disturbed soils (either from burning or tillage). It is very easy to hand-pull from the soil, but its numbers are often too great to remove by hand.
Dr. Jeff Derr offers control recommendations: American burnweed (Erechtites hieracifolia) is a summer annual in the aster family that is wind dispersed. It is an upright growing plant that can get pretty tall (up to 3 ft at maturity). It appears usually in late April – mid-May so it often has not germinated when glyphosate or other winter POST herbicides are applied to dormant warm-season turf. The preemergence crabgrass herbicides like prodiamine, pendimethalin, etc. provide poor control of this weed. Isoxaben provides fair control. Probably best to go after this weed with a 3 way postemergence broadleaf herbicide when it is small and actively growing.
