Cool control
1 Mar, 2006 By: David Gardner Landscape ManagementNew herbicide technologies make weed management in cool-season turfgrass easier.
Perhaps not since the early 1990s have we seen as many promising new chemistries for selective weed control in cool-season turfgrass. In addition, more materials are in development and will likely receive registrations soon. Beyond just having new herbicides for our weed control arsenal, many of these new materials offer selectivity and timing options that, as recently as five years ago, we thought would likely never be possible.
Control at establishment
One of the difficulties of establishing turf from seed is competition from weeds. This competition is compounded by the fact that almost all existing herbicides will also damage or kill the germinating turfgrass.
 Crabgrass (Digitaria sanguinalis) |
Most herbicides state on the label that the turf requires mowing three times before it is mature enough to safely withstand the herbicide application. With fall seeding operations this is perhaps less of a problem, since crabgrass and other annual grass germination pressure is minimal. Also, with an August or early September establishment, the grass has usually been mowed three times by November, which is the primary month for perennial broadleaf weed control in cool-season grass regions.
However, with establishment in spring, there is often not enough of a difference in the germination time of cool-season turf and that of crabgrass or annual broadleaf weeds. The competition from these weeds can make it difficult to nearly impossible to establish turf in the spring.
 Dandelions (Taraxacum officinale) |
Two products labeled for control of weeds in newly seeded cool-season turf are the traditional choices: siduron and bromoxynil. Neither of these products is as effective as other herbicides used in cool-season turf, but their safety to turfgrass seedlings makes them a good option.
However, research conducted at major universities shows that a recent introduction, carfentrazone (sold as Quicksilver by FMC) provides safe and effective control of germinating broadleaf weeds in a newly seeded stand of either Kentucky bluegrass (Poa pratensis) or perennial ryegrass (Lolium perenne). The label for Quicksilver has been updated to allow application to these species seven days after emergence. Carfentrazone is a fast-acting contact herbicide that is recommended as an addition to systemic herbicides, such as 2,4-D or triclopyr, in order to hasten burndown of the weed. Note that since carfentrzone is a contact herbicide, it effectively controls germinating annual broadleaf weeds in a newly established turf. However, it's not as effective against mature broadleaf weeds during an overseeding operation.
A further promising development for springtime weed control at establishment is with quinclorac (marketed as Drive by BASF). Quinclorac is labeled for application any time before or after establishment of tall fescue. Research shows that quinclorac can safely be applied to either Kentucky bluegrass or perennial ryegrass as few as seven days after seedling emergence.
 White clover (Trifolium repens) |
Results of recent tests at The Ohio State University also indicate that not only can a combination of quinclorac and carfentrazone be applied to 7-day seedlings of either of these species, but that delaying the application to 14 or 21 days after emergence results in decreased weed control. Likely, the herbicides become less effective as the weeds become more mature and capable of competing with the germinating turfgrass.
There was some slight phytotoxicity with the 7-day application, but the turf outgrew this by day 14. It appears that competition from weeds should be less of an issue during springtime establishment than it has been in the past.
Selective control of perennial cool-season grasses
Normally desirable turfgrass species growing in an inappropriate environment, such as creeping bentgrass (Agrostis palustris syn. A. stolonifera) or common types of tall fescue (Festuca arundinacea) growing in a Kentucky bluegrass/perennial ryegrass lawn are difficult to control.
Chlorsulfuron is labeled for the selective removal of tall fescue from Kentucky bluegrass. It is effective, but usually requires time and multiple applications. Until recently no other herbicide chemistries were available that could selectively remove one cool-season turfgrass species from a stand of another.
1 2 3
Please send any technical comments or questions to our webmaster.