Herbicide Control of Melaleuca
Chemical control consists of herbicide application of various types such as aerial spraying or broadcasting of granular products. Chemical treatments are often combined with mechanical treatments for more effective control. For example, hack and squirt is actually a combination of mechanical and chemical treatment where we girdle the trees and spray the exposed cambium layer with herbicide to kill the tree.
Not all plants are susceptable to herbicides, and controlling invasive plants sometimes (and unfortunately) becomes a lesson in futility. Fortunately, we don't have that problem with melaleuca because the tree is quite susceptable to herbicides. Difficulty arises however, with applying the selected herbicide. For example, the foliage of small trees can be sprayed with a hand or backpack sprayer, but these tools cannot be used to spray large trees. Herbicides containing imazapyr (such as Arsenal) or glyphosate (Roundup, Glypro, Glyfos, and many others) are the most commonly used. Triclopyr (Brush B Gon and Brush Killer, among others) can be used on melaleuca stumps. All the herbicides mentioned are nonselective, and can kill other plants, including trees, in the area.
For large stands of melaleuca trees (acres) with relatively few native plants, aerial application of herbicides is often used. The South Florida Water Management District mixes imazapyr and glyphosate with water (3 quarts/3 quarts/20 gallon solution), plus surfactant.
If melaleuca trees are mixed in a forest with native species (such as slash pine or pond cypress), selectively killing melaleuca trees by hand might be the best choice. To do this, the corky bark is cut away, and herbicide is sprayed onto the cambium. This technique is often called hack-and-squirt, and for more details, check out the hack-and-squirt slideshow.
If melaleuca trees are cut down, the remaining stump should be sprayed with a herbicide to prevent regrowth (known as coppicing). Herbicides to be used for this include glyphosate and triclopyr. The stump treatment slideshow gives more information.