The best defense against weed encroachment is a dense stand of healthy turf. That said, even in the healthiest areas summer annual weeds such as crabgrass and goosegrass can still be problematic, especially if they have been an issue in the past. Aside from sound management practices that promote healthy turf, a sound preemergennce herbicide program often provides the cheapest and most effective option for controlling troublesome summer annual weeds. As the adage goes, “An ounce of prevention is worth a pound of cure.” Some herbicides are more effective than others against particular weeds, so product selection is key.
Preemergence herbicides often provide a high percentage of control, but 100% control is unlikely. In areas where weeds have been problematic in the past, breakthrough is more likely to occur. For example, 99% control is pretty good if there are only a handful of seeds in the soil seedbank, but if there are millions of seeds, then 99% control doesn’t sound quite as good.
If weeds have broken through, postemergence herbicides and hand picking become the only option. Rate, timing, frequency and product selection all impact the efficacy of these applications. More often than not, these products need to be applied when the weeds are immature to provide good control. Unfortunately, once summer annuals like goosegrass and crabgrass mature, they are more difficult to control and begin to crowd out desirable turf. If populations are high and weeds reach maturity, it can become a problem even if weeds are killed because it will leave large voids in the turf, requiring some sort of recovery.
When it comes to weed management, success breeds more success. Good control year after year results in fewer seeds in the soil seedbank and less pressure in future years. If weeds got out of control this year and you are considering postemergence products, remember that a recovery program will need to be implemented in areas where large voids in turf coverage develop after the weeds have been eliminated. If you would like to discuss your weed management program with a USGA agronomist, we would be happy to hear from you.
Central Region Agronomists:
Paul Jacobs, agronomist – pjacobs@usga.org
Zach Nicoludis, agronomist – znicoludis@usga.org
Information on the USGA’s Course Consulting Service
Contact the Green Section Staff