Mimosa

In contrast to the situation with kudzu and sericea lespedeza, which were widely planted for forage in the Southeast before concerns developed about their invasiveness, the invasiveness of mimosa is currently recognized with only potential as a forage plant established. An apparently obvious conclusion is that this potential usefulness is offset by the risk, which should therefore preclude any further consideration for forage use. A basis for continuing recognition of the forage potential of mimosa, however, is provided by the promise of future technological developments. Ranney [2004] presented the concept of research in progress to develop seedless triploid varieties of several horticultural species including mimosa. Such varieties can be produced by hybridizing a tetraploid with a diploid of the species to produce seed for propagation of a non-seed-producing triploid generation. Triploids can also be produced by generation of plants from naturally triploid endosperm tissue. In either case, further multiplication for field plantings of mimosa can be made vegetatively by rooting stem cuttings for generation of transplants. Thus, depending on source of future seedless mimosa varieties, seed for a terminal generation or vegetative propagation of transplants could provide pastures of non-invasive mimosa.

A seed propagated variety of non-invasive mimosa would likely be more economical than one dependent on vegetative propagation. A sustainable system would, however, require more intensive management than typical for perennial grasses in the region to maintain the necessary balance between excessive woody growth and defoliation-induced mortality [Pitman, 2008]. The comparatively high nutritive value of mimosa and potential for use as grazed pasture or harvested forage in systems similar to tropical cut-and-carry methods may provide opportunity for novel, intensively managed, economically viable livestock agriculture with limited external inputs. Such possibilities are sufficiently promising to be the basis for a U.S. patent on one such pasture-based system titled "Process for Propagation and Utilization of Mimosa" [Bransby et al., 2003]. Alley-cropping and other agroforestry systems based on mimosa have also been evaluated [Matta-Machado and Jordan, 1995; Rhoades et al., 1998; Addlestone et al., 1999; Burner et al., 2008].

The various pests of mimosa in the Southeast may, therefore, be considered beneficial for control of existing unwanted populations or potential problems for a rather intensively managed mimosa crop. Nematodes and Fusarium wilt [McArdle and Santamour, 1986], mimosa webworm [Santamour, 1990], the beetle Agrilus subrobustus [Westcott, 2007], and the psyllid Acizzia jamatonica [Ulyshen and Miller, 2007] are among an apparently growing list of mimosa pests. Abundant seed production, wide adaptation, root sprouting of damaged trees, and dispersal of seedpods by wind for short distances and water for greater distances contribute to the spread of this species in disturbed areas and along forest edges in the Southeast. Recommendations for control primarily involve herbicide applications, including injection of individual trees when practical [Miller, 2003]. Competitive ability under a forest canopy is poor [Smith et al., 2001], and grazing prevents establishment of seedlings in pastures. Even though grazing typically prevents establishment of mimosa, grazing does not provide a realistic short-term remedy for established trees. Smith et al. [2001] noted that mimosa does not often persist for more than 30 years without renewed disturbance. In Louisiana, mimosa populations dominating small areas are often in obvious decline within 10 years. Plants defoliated periodically, such as with infrequent roadside mowing, typically regrow vigorously and do not exhibit the symptoms of decline apparent on plants allowed to grow to maturity. This regrowth vigor is a key aspect of the forage potential of the species. Maintaining such a vegetative growth stage restricts both pest-induced mortality and seed production. Thus, mimosa under intensive management as a grazed forage crop would have limited opportunity to contribute to invasiveness. As often occurs with perennial plants however, cessation of management could provide a source of seed for new invasions.

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