Poa annua contamination is a problem for landscape superintendents around the world. Embark is one plant growth regulator that effectively suppresses Poa annua seedheads, but there is potential for turf discoloration.

Cutting down on the chore of mowing has always been a dream of the professional turfgrass manager. While we haven?EUR??,,????'???t gotten to the point where mowing is a thing of the past (which, come to think of it would put us all out of a job), there are a number of compounds that have the ability to slow the growth of grasses and consequently reduce the mowing requirements.

This becomes particularly important during periods of rapid growth such as in the spring for cool season grasses and summer for warm season grasses.

Color Enhancement

From the beginning of PGR use on turf, superintendents have observed color changes when these products are used. With the earlier Type I materials, there was often a negative effect and turf discoloration was common. With the GA inhibitors, however, improvements in turf color are often observed.

This is particularly true with trinexapac-ethyl (Primo), which often results in a darker green color of treated turf. Reduced growth and improved color are a very beneficial combination on highly maintained turf. As is usually the case with PGRs, this response can be highly variable.

Overseeding

PGRs have been employed as a tool to improve overseeding of cool season grasses into warm season turf. The goal is to slow the growth of the warm season grass without inhibiting the establishment of the cool season seed lings. Timing is critical to prevent inhibition of the cool season seedlings and results may be quite variable. Trinexapac-ethyl (Primo) tends to be one of the best PGRs for this purpose because of its foliar absorption and its reduced likelihood of inhibiting the cool season seed germination. A critical factor in using trinexapac-ethyl for this purpose is that it be allowed to dry on the bermudagrass tissue before overseeding takes place. Label recommendations suggest applying Primo one to five days before seeding.

A Poa annue-infested sod strip was left untreated down the center of a golf course fairway. The strip stands out amongst fairway turf that has been treated to suppress Poa annua seedheads.

Water Use

PGRs reduce growth, but does this translate into a reduction of water use? Research in Australia 15 showed a 25% to 30% reduction in water use rate on tall fescue treated with trinexapac-ethyl. There is a great deal of interest in this subject, particularly in arid regions, and more work is needed on a variety of species.

Freezing Damage

In northern regions, freezing damage can be a serious problem. PGRs slow growth, thicken cell sap, and may provide an antifreeze like effect. Rossi and Buelow (1995) observed enhanced freeze tolerance of annual bluegrass treated with low rates of trinexapac-ethyl. However, Dunn et ai. (1999) found no reduction in freezing damage on zoysiagrass treated with this product. Northern superintendents who often experience Poa annua loss during the winter may want to experiment with this idea.

Fungicides

One of the factors that limits fungicide efficacy is plant growth, or when the contacts are mowed off soon after application. PGRs tank mixed with fungicides show promise in extending efficacy and in reducing the fungicide rates needed for disease control. Some PGRs may even directly suppress dollar spot on treated turf.

Other Observations

Research has shown that PGRs can improve shade tolerance of certain species, particularly zoysiagrass. Trinexapac-ethyl is now being widely used for this purpose in the transition zone of the United States and through out the Orient.

Source: Dr. Nick Christians, Iowa State University Department of Horticulture