Turfgrass Establishment Series – Nonselective Weed Control
One of the necessary steps for a successful turf renovation or establishment may be the use of a nonselective herbicide. There are two reasons why a nonselective herbicide may be used. One is if there is a desire to change the species or cultivar of turfgrass that is being managed. The other reason is if there are many weeds that cannot be controlled with selective herbicides (Figure 1). Most weeds for which we do not have selective herbicides are of two types: 1) cool season grasses that are growing out of place (rough bluegrass, quackgrass, orchardgrass, and timothy, for example), or 2) savannah type (chloridoid) warm season turfgrasses (bermudagrass and nimblewill, for example).
Dazomet (sold originally as Basimid) is a fumigant/soil sterilant. This may be used in instances where glyphosate is not effective or if there are many weed seeds in the soil. It’s applied as a granule. For optimal effectiveness this product needs to be applied with a large amount of water or, preferably, tarped (which requires a means of getting the water under the tarp). It can be difficult to use, and the results can be inconsistent, especially if trying to control bermudagrass. Also, it has the potential to move off target if heavy rainfall occurs.
The alternative is that there are several nonselective herbicides on the market. Only one of these, glyphosate (sold originally as Roundup), is systemic. Another herbicide, glufosinate (sold originally as Finale), is locally systemic. However, this limits its overall effectiveness compared to glyphosate. Thus, even though it is controversial, glyphosate remains the only herbicide presently registered for nonselective weed control that is a true systemic thus it is what is usually recommended for renovation purposes.
One useful property of glyphosate is that it will not travel, seep or leach following application, unless applied to a very sandy soil, and this minimizes the risk of off target movement. In fact, glyphosate will almost always bind very tightly to the soil following application. The label varies depending on the product as to what the reseeding interval is, so make sure to read the label. However, weeds germinating from seed following a glyphosate application will not be controlled. For this same reason, you can apply turfgrass seed soon after a glyphosate application. That said, it best to apply glyphosate a couple weeks prior to the intended seeding date and then wait to observe if any weeds attempt to regenerate from below ground. This allows for a second application of glyphosate, if necessary, prior to seeding. Follow the label for the recommended rate of application, which will vary depending on the weed pressure present.