Grassy Weed Control Update - 2025
For best control of grassy weeds, the most important step is to identify the weeds and to recognize that the herbicide recommendations differ among species. For example, goosegrass is better controlled with fenoxaprop or topramezone and quinclorac is not as effective. Barnyardgrass is better controlled with fenoxaprop or topramezone while field paspalum can only be reliably controlled with topramezone. There are vegetative structures you can use for identification, such as the ligule and auricle and for certain grasses these can be very reliable. Quackgrass has a large clasping auricle and orchardgrass has a large prominent ligule while barnyardgrass has no ligule. For many grasses that lack large, obvious structures it can be much more complicated to try to identify them. When available, the seed head is the most reliable structure to identify a grassy weed (Figure 1). If in doubt, try to find an area that’s not visible to the client and let a few plants mature and produce a seed head so that you can verify its identity. The figure includes a picture of the seedhead of some of our most common grassy weeds as well as prominent vegetative structures that are useful for identification.
Crabgrass can be controlled postemergence with fenoxaprop, quinclorac, mesotrione or topramezone. The issue of when to apply the herbicide for postemergence control is complicated. The bigger the weed, generally, the more difficult control will be. But control of leaf stage crabgrass in June will often result in more crabgrass germination following herbicide application. Timing is also dependent on product used. Fenoxaprop tends to be very effective on leaf stage crabgrass, but its control of tillering crabgrass is variable. I have seen applications of fenoxaprop to 5-tiller crabgrass that were very effective and others where it barely injured the crabgrass. The conventional wisdom is that fenoxaprop is most effective on leaf-stage or early tillering crabgrass. Quinclorac is effective on leaf stage crabgrass and late stage (>5 tiller) crabgrass but can be frustratingly inconsistent when crabgrass is between 2 and 5 tillers (roughly June 15 to July 1 in central Ohio). Topramezone seems the most flexible when it comes to the stage of crabgrass at application. That said, and this applies to whichever herbicide you use, if you make a postemergence application before weed seed has stopped germinating, in most cases you will get a few weeks of suppression followed by a new population of crabgrass from seed. Thus, lasting control of crabgrass tends to occur with applications made after July 1. For late stage (>6 tiller) crabgrass, research conducted at The Ohio Turfgrass Foundation Research and Education Center has found that application of a ½ label rate of quinclorac (e.g. Drive) combined with either a ½ label rate of topramezone (e.g. Pylex) or a ½ label rate of mesotrione (e.g. Tenacity) provides best control. This combination has provided better than 95% control in our trials.
Goosegrass looks somewhat like crabgrass from a distance, but it tends to distinctly radiate from where it roots and the leaf sheaths are bleached out. For this reason, it is sometimes also called silver crabgrass. When it flowers, it looks sort of like a crabgrass inflorescence. However, instead of individual flowers, they are in clusters. Barnyardgrass has a coarser appearance and a seedhead that has branching along the flower stem, rather than all originating at one point like crabgrass and goosegrass. Goosegrass, barnyardgrass and yellow foxtail are all most effectively controlled with either topramezone or fenoxaprop. Note that quinclorac is not effective for the control of these grasses.
Savanah grasses such as nimblewill and bermudagrass are warm season species that form patches of bleached out turf in cool season turf during the winter months. These two can be easily identified when they flower – nimblewill (not pictured) has a single spike while bermudagrass has a seedhead like crabgrass that is 3 spikes that radiate from the end of the flower stem (Figure 1). With either species, control is usually best achieved with repeat applications of a non-selective herbicide. There is some potential to achieve selective control with repeat applications of either mesotrione or topramezone, though this may not be as consistent or reliable of a control strategy. Consult the label for specifics.
There is one perennial species that is tropical, field paspalum, that can survive repeated mowing and for which there is a good selective postemergence herbicide. It can be controlled postemergence with one or two applications of topramezone. Remember that since it is a perennial no preemergence options are available. Instead of small seedling leaves in the spring you will see full size leaves emerging in the turf. The cool season perennial grasses are more difficult to control. Quackgrass, orchardgrass and others are best controlled with a non-selective herbicide. Sometimes repeat applications are required, followed by renovation.