 |
|
|||||||||||||||||||||||
A widely used groundcover, Wedelia has become a weed problem in many lawns. A member of the Compositae or sunflower family, Wedelia is a soil creeper. It spreads vegetatively, rooting at the nodes, and forms a thick carpet. It's Latin name Wedelia trilobata is based on the lobed appearance of individual leaves. It's fairly common in Florida, and there is even a Wedelia Drive, in Barefoot Bay, Florida. In its pure form, Wedelia is attractive. To be more specific, I consider it attractive. Remember, what one person considers a flower is a weed to someone else. Wedelia has orangish flowers that can easily be mistaken for beach sunflower, another creeper. Unlike beach sunflower, a native which confines itself to natural areas, Wedelia is an introduction from tropical America, and it grows primarily in human-created habitats, e.g., the irrigated lawns. That's not to say it will not escape into conservation areas occasionally, and the Florida Exotic Plant Pest Council classified it as a Category II invader in their 1997 plant list (see links, below) and that listing continued through 1999. Removal of Wedelia had been cited in 1996 by Martin County Environmental Planning Department (link broken) as a requirement for implementing a site plan. The other problem with Wedelia is that it invades lawns. In American culture, most observers' perception of the lawn is that it supposed to be reasonably low and uniform. In south Florida, most of our lawns are planted as monocultures of Floratam St. Augustinegrass. Floratam is a variety that was developed by the University of Florida in 1973, and represents the majority of the $200 million sod sold each year. One can argue in favor of uniformity because if you can see the landscape surface, it's safer and you're less likely to trip on something or get bitten by a snake or a rat. I happen to like snakes and rats, but think they are better off in the bushes than in my yard. So rather than my continuing to harp on the "what's a weed" debate, let's discuss how to keep Wedelia and how to get rid of it. Ideally, if you plant Wedelia, it should be for a conservation purpose, such as a hard-to-reach location. It does not persist in very dry areas, at least not in a solid stand. So by-and-large it will not serve for erosion control, as it will leave major gaps where erosion can get started. Unless you irrigate or plant it in a naturally moist area. Aesthetically, the plant tends to get pretty ragged over a few years, and still requires mowing to keep it looking nice, but there's hardly any mower tall enough to cut it properly. Despite the orangish flowers, which are attractive, probably the best thing that can be said about Wedelia is that it grows good. In fact, it is recognized to be impossible to get rid of, so if you must plant it, it is best to do so in a confined area surrounded by sidewalks or large landscape timbers. It does not have underground rhizomes, but the aboveground stolons can advance very quickly.
Rachel Carson, author of Silent Spring, talked about the appropriate use of herbicides to manage roadside vegetation. She was referring to 2,4-D. This may seem surprising, because she was painted by others as such a radical. Visionary yes, but extremist, no. The majority of her book was about the harmful misuse of chemicals in the environment. I agree that if we're reasonably sure something is harming wildlife, we should should stop it. But here was a book that also talked about the judicious and beneficial use of 2,4-D in the environment. 2,4-D in its pure form has low mammalian toxicity, and used responsibly is a valuable management tool, especially for the protection of grass from competition by most herbaceous dicots or broadleaf plants. Unfortunately, it has been recognized to be rather harsh on St. Augustinegrass. In the early 1950s, Florida St. Augustinegrass sod producers started evaluating 2,4-D on their fields, and they found that it made the stolons of the grass brittle. 2,4-D is even worse on selected families of broadleaf plants, such as tomato and cotton. Drift from the older formulations of 2,4-D has been known to kill crops a couple counties downwind. But those serious problems you might expect, because they have occurred from aerial spraying. The new amine and other formulations of 2,4-D have much less volatility and are much less likely to move away from their target. As with any pesticide (and weed killers, that is herbicides, are a kind of pesticide) one must use the formulations of 2,4-D responsibly according to the label. Reports in the 1980s of lawn damage in Florida from 2,4-D and related chemicals eventually caused some of the formulators to label their products, "not to be used on Floratam St. Augustinegrass in Florida." It was not clearly determined whether these were instances of overapplication, sensitivity of Floratam, or formulation. Most weed killers are distributed only to professional applicators, who know how to use the products, and are specially trained and licensed to do residential pest control. 2,4-D is normally formulated in combinations with three or four other related chemicals, including MCPA, MCPP, and dicamba. Unfortunately, it's difficult to tell the individual effects of each chemical, least of all their combined effects in a mixture. What I am discovering is that some combinations containing MCPA are almost as harmful to St. Augustinegrass, whereas those which are primarily 2,4-D have the greatest impact on removing Wedelia, and also are safest to St. Augustinegrass. I am continuing to evaluate these chemicals in typical condominium settings, because that's the most accurate way of determining their potential usefulness. These are old chemicals that may have a new life some day. The only other broadleaf weed killer for St. Augustinegrass, atrazine, has been found in well water in the corn belt United States, and some wonder how long its going to be available for use in lawns. Description, Florida Exotic Plant Pest Council Invasive Plant
List, Ground
covers, Accumulator
of Cadmium and Nickel, National Agricultural Library Coumarins
from Wedelia in neuropathic medicine, Poisoning
of pigs from Wedelia glauca, Aggie-horticulture,
|
||||||||||||||||||||||||
|
