This month, I published a scientific paper in the journal HortScience showing that canopy light gaps in bermudagrass turf, in the form of divots, stimulate goosegrass seed germination and growth. It is only common sense that maintaining dense turfgrass canopy reduces goosegrass opportunities and reduces the need for chemical herbicides. This study adds strong quantitative data to a scientific model for cultural management of turfgrass weeds.
Goosegrass produces billions of seeds per acre and is a common and difficult weed to control in Florida golf courses and sports fields. Postemergence herbicides that kill goosegrass can harm bermudagrass turf and are largely ineffective against large plants. Preemergence herbicides can prevent goosegrass seedlings from coming up in temperate climates, when timed with weed germination in Spring. But in the subtropics, such as South Florida, goosegrass seeds are produced and germinate year-round and there is not one good time for preemergence herbicides here.
The research study, which I conducted in a glasshouse at the University of Florida / IFAS, Fort Lauderdale and Education Center, shows a pathway for cultural management of goosegrass. Seedling emergence was reduced 72% by allowing divots to grow back. And goosegrass seedling growth was reduced 90% in closed bermudagrass canopy, compared with planting in divots. High rate of nitrogen fertilization of bermudagrass, maintaining dense canopy long-term, also reduced goosegrass germination. But in the first few weeks after divots were created, fertilization stimulated goosegrass emergence.
So, based on the data, the recommendation to reduce goosegrass establishment is:
- Maintain well-nourished turf, free of divots or other holes in the canopy.
- When divots do occur, don’t fertilize them as that encourages goosegrass germination.
- Fill new divots with clean sand.
Against goosegrass, and some other serious weeds, cultural management is an alternative to herbicides. It has long been said that maintenance of healthy turfgrass is a way to prevent or reduce weeds, but the definition of “healthy” was not clear. Now this research shows that the focus should be on canopy density as the basis for cultural management, to prevent or reduce goosegrass seedling emergence and growth. And canopy density probably also explains the benefits of taller mowing height and higher nitrogen fertilization rates that I earlier demonstrated in a meta-analysis of published literature on crabgrass infestation in cool-season turfgrasses.
The three primary turfgrass cultural management practices, mowing, watering, and fertilization, which we would do anyway to keep turfgrass looking nice, can be adjusted to reduce or prevent weeds. Moderation and consistent timing are the keys. This scientific paper joins a series of papers showing how to reduce weeds without herbicides, or with less use of herbicides.