A Management Guide for Invasive Plants in Southern Forests James ...

40Water-Level ManipulationIn areas where water level can be manipulated, flooding or drawdowns can reduce invasiveplant species in aquatic and wetland habitats but is usually not effective as a stand-alonetreatment. This method is species and site specific. For effective outcomes, managersmust first understand the biology of both invasive and native plants in the treatment area.Water-level manipulation works by either lowering water levels to kill invasive plants thatcannot tolerate exposure to dry and hot conditions or raising water levels to kill invasiveplants that cannot tolerate submergence or water-logged soils. However, both processescan spread floating seeds of invasives and make habitats more vulnerable to nonnativeplant establishment. Lowered water levels in spring and summer can also facilitate herbicideapplications in wetlands for controlling such plants as alligatorweed [Alternantheraphiloxeroides (Mart.) Griseb.].Biological Control MethodsBiological control, or biocontrol, of plants uses living organisms to weaken, kill, or stop seedproduction of a targeted invasive plant. The most common agents in biocontrol programsare insects and pathogens, and uses of nematodes and mites are under study.Alligatorweed herbicidesprayed after lake levellowered.Classical biocontrol involves finding agents in the home range or similar habitat ofthe invasive plant, followed by intensive research on feeding habits and reproduction,and a planned introduction of plant-specific agents into invaded areas. The goal is toidentify predators that are host specific to the target invasives, i.e., they will not attacknative plants, and will increase and spread in the new range to permanently suppressthe invasive species. Classical biocontrol has an initially high public cost due to anoften lengthy search for the right agent, extensive feeding tests in special quarantinefacilities, coordinated releases, and long-term monitoring. There are specific requirementsthrough a series of scheduled oversights by a Federal Government interagencycommittee requiring documented studies to strictly control biocontrol agent releases.Following release, nontarget damage is very rare but has occurred with the classicexample of the musk thistle head weevil (Rhinocyllus conicus Frölich, 1792) attackingnative thistles. In general, scientific evaluations of past releases have shown that thebenefits from biocontrol over a region outweigh the detriments.Gary BuckinghamClassical biocontrol programs in the southern region are under development for tallowtree[Triadica sebifera (L.) Roxb.], Chinese privet, and tropical soda apple (Solanumviarum Dunal), and in Florida for Old World climbing fern also known as small-leafclimbing fern [Lygodium microphyllum (Cav.) R. Br.]. Successful projects underwaytarget purple loosestrife (Lythrum salicaria L.), melaleuca [Melaleuca quinquenervia(Cav.) S.F. Blake], and alligatorweed.Agasicles hygrophila adults andlarvae devour leaves and upperportions of stemsAugmentative and inundative biocontrol identifies native insects, pathogens, nematodes,and mites that feed upon nonnative invasive plants in this country. When the appropriateagents are discovered and researched, there is an attempt to release large numbers of theminto high infestation areas of the invasive plant. A program under development for kudzuuses this method. This program and other prior efforts have used pathogens and havebeen formulated into sprays, often referred to as bioherbicides. The challenge has been tomaintain the viability of the pathogen or spores during packaging, shipment, application,and residence on the target foliage.Prescribed GrazingPrescribed grazing is an approach that relies on cattle, sheep, goats, and horses to reduceinfestations. Grazing is a potential control treatment when the invasive is palatable and theinvasive plant is not poisonous to the animal. Cattle and horses are useful for many herbaceousinvasive plants, while sheep and goats will feed on woody plants as well. Goats willdefoliate and debark shrubs, saplings, and small trees to a higher level than sheep, eventhorny vegetation. The animal species is important as is the breed, the best being thosebreeds that are larger and can handle difficult grazing and browsing conditions.Horses grazing cogongrass.