Studies to develop Melaleuca control tactics using fire and herbicides

Myers, Ronald; Belles, Holly

In spite of several decades of control efforts, the Australian tree, Melaleuca guinguenervia, has exhibited phenomenal spread in south Florida wetlands. Effectiveness of certain herbicides on melaleuca has generally been overestimated, continuing the use of some ineffective chemicals. Because melaleuca is a highly fire-adapted species (flammable foliage, thick protective bark, fire-induced seed release, and sprouting), burning melaleuca-infested native habitats is generally avoided. Big Cypress National Preserve contains many diverse natural areas susceptible to the invasion of melaleuca. Melaleuca presently infests approximately 60 square miles of the Preserve. The current treatment strategy is to slow the rate of spread by targeting outlying individuals which serve as loci for rapid infestation of new areas. From 1984 to 1991, 639,000 saplings have been pulled and 801,000 trees have been treated with herbicide. The studies described in this report point to control strategies combining fire, environmental stresses, and herbicides that may allow for containment and control, provided treatments are timed appropriately and applied judiciously. Arsenal stump treatment appears to be the most effective in killing melaleuca and has become the treatment of choice in the Big cypress National Preserve. There are no major seasonal differences in herbicide effectiveness. Results from foliar application of herbicides varied widely, and do not support the use of aerial applications as a reliable control method. cutting melaleuca and letting the stumps flood was found to be very effective in killing melaleuca if the period of submergence was several months long. One of the most effective uses of prescribed fire is to burn an area 6-12 months following herbicide treatment to kill seedlings established after seed release. Fire is less effective once saplings reach a meter tall. Fire rarely kills reproductive individuals, but there are instances where it can be used to reduce flowering and seed production. One use of fire originally proposed was to use fire as a stressor before applying herbicide. However, because some herbicides were nearly 100% effective without burning, and the seed release triggered by burning may result is seedlings that cannot be killed by follow-up burns, it seems best to treat with herbicide before burning.