Ideally, a perennial turfgrass cover can be maintained relatively free of weeds. Preventive control is based on considerable anecdotal information, but surprisingly is undocumented for warm-season turfgrasses. Excessive irrigation usually is a requirement for certain lawn weeds, e.g., dollarweed, Hydrocotyle umbellata L., and sedges, Cyperus spp. in St. Augustinegrass. Improper soil sanitation contributes to the distribution of torpedograss, Panicum repens L., in the urban landscapes. The inadvertent production and dispersal of seeds of goosegrass, Eleusine indica L., contributes to its distribution in compacted athletic bermudagrass turf. A pure stand of goosegrass can produce 500 thousand seeds per m2 (Holm et al., 1977). Alleviation of soil compaction is an important means of reducing populations of goosegrass, the main weed of Florida golf and athletic turf. Regular maintenance (proper mowing, irrigation, and fertilization) contribute to healthy turfgrass, and have long been the main means of controlling weeds. These methods have been rarely proven scientifically or integrated into an expert system to assist turf managers in Florida.

Among 245 scientific papers on warm-season turfgrass weeds and PGRs, 224 emphasize chemical control and PGRs, and the remaining 21 papers emphasize some other aspect such as weed biology, fertilization management, identification, and competitiveness. Only 8 papers, or 3%, test non-herbicidal weed management concepts, mostly the effect of fertilization practice on weeds in zoysiagrass, an uncommon genus in Florida. Of all 245 papers, most, 73%, deal with bermudagrass, and only 18% deal with St. Augustinegrass or bahiagrass, the two main turfgrasses in Florida.

What makes a good turf weed? Perhaps if we knew, we could better prevent and control weeds. Physiological adaptations of kikuyugrass, Pennisetum clandestinum, were shown to be important (Wilen and Holt, 1996). There have been attempts to model the growth characteristics of bermudagrass in Israel (Horowitz, 1972) as well as to understand the growth characteristics of turf species (Busey and Myers, 1979). Little research has been done on the biology of turf weeds.

Among the weed biology papers, inundative biological control of weeds by microorganisms is receiving more attention (Hasan and Ayres, 1990). Xanthomonas campestris pv. poannua has shown promise for biological control of annual bluegrass (Johnson, 1994; Johnson et al., 1996). Bipolaris setariae (Saw) and Piricularia grisea (Cke.) Sacc. are highly infective of goosegrass, but are highly dependent on environmental conditions (Figliola et al., 1988), and have not been tested in a turf setting, probably because of possible nontarget effects on turfgrass species. For some introduced weeds, inoculative biological control by insects may be an alternative worth evaluation. Would alligatorweed in sod fields be controlled biologically if the flea beetle was not a non-target casualty from the use of insecticides?

Among papers dealing with turf herbicides, there has also been very little documentation on application method, except tank mixtures, which are frequently tested. Iron has been shown to be highly effective in reducing the discoloration from certain herbicides (Johnson et al., 1990). Postemergence grass herbicides applied in ultra-low volume (9.4 L/ha) in oil diluents maintain annual grass control equal to that achieved with higher herbicide rates in larger volumes of water (Bohannan and Jordan, 1995).

References

Bohannan, D. R. and T. N. Jordan. 1995. Effects of ultra-low volume application on herbicide efficacy using oil diluents as carriers. Weed Technology 9:682-688.

Busey, P. and B. J. Myers. 1979. Growth rates of turfgrasses propagated vegetatively. Agron. J. 71:817-821.

Figliola, S. S., N. D. Camper, and W. H. Bidings. 1988. Potential biological control agents for goosegrass (Eleusine indica). Weed Science 36:830-835.

Hasan, S. and P. G. Ayres. 1990. The control of weeds through fungi: Principles and prospects. New Phytologist 115:201-222.

Holm, L. G., D. L. Plucknett, J. V. Pancho, and J. P. Herberger. 1977. The world’s worst weeds: Distribution and biology. The University Press of Hawaii, Honolulu.

Horowitz, M. 1972. Spatial growth of Cynodon dactylon (L.) Pers. Weed Research 12:373-383.

Johnson, B. J. 1994. Biological control of annual bluegrass with Xanthomonas campestris pv. poannua in bermudagrass. HortScience 29:659-662.

Johnson, B. J. 1990. Response of bahiagrass (Paspalum notatum) to plant growth regulators. Weed Technology 4:895-899.

Johnson, D. R., D. L. Wyse, and K. J. Jones. 1996. Controlling weeds with phytopathogenic bacteria. Weed Technology 10:624

Wilen, C. A. and J. S. Holt. 1996. Physiological mechanisms for the rapid growth of Pennisetum clandestinum in Mediterranean climates. Weed Research 36:213-225.

27 November 1998