Control Techniques and Management Strategies for the Problematic Navua sedge (Cyperus aromaticus)

Abstract

Navua sedge, a member of the Cyperaceae family, is an aggressive weed of pastures in Fiji, Sri Lanka, the Malay Peninsula, Vanuatu, Samoa, the Solomon Islands, and Tahiti and is now a weed of pastures and roadsides in north Queensland, Australia. Primarily restricted to areas with an annual rainfall exceeding 2,500 mm (98.4 in), Navua sedge is capable of forming dense stands, smothering many tropical pasture species. Seventeen herbicides were field tested at three sites in north Queensland, with glyphosate, halosulfuron, hexazinone, imazapic, imazapyr, or MSMA as the most effective for Navua sedge control. Environmental problems, such as persistence in soil, lack of selectivity, and movement off-site, may occur using some herbicides at the predicted 90% lethal concentration (LC90) control level rates. A seasonality trial using halosulfuron (97.5 g ai ha−1[1.4 oz ac−1]) gave better Navua sedge control (84%) by spraying in March to September than by spraying at other times (50%). In a frequency trial, sequential glyphosate applications (2,160 g ae ha−1) every 2 mo was more effective for continued Navua sedge control (67%) than a single application of glyphosate (36%), although loss of ground cover would occur. In a management trial, single applications of glyphosate (2,160 to 3,570 g ae ha−1) using either a rope wick, ground foliar spraying, or a rotary rope wick gave 59 to 73% control, whereas other treatments (rotary hoe, 3%; slashing, −13%; crushing, −30%) were less effective. In a second management trial, four monthly rotary wick applications were much more effective (98%) than four monthly crushing applications (42%). An effective management plan must include the application of regular herbicide treatments to eliminate Navua sedge seed being added to the soil seed bank. Treatments that result in seed burial, for example, discing, are likely to prolong seed persistence and should be avoided. The sprouting activity of vegetative propagules and root fragmentation also needs to be considered when selecting control options.

Germination biology of three populations of Navua sedge (Cyperus aromaticus)

“…It is a native of tropical Africa but has now spread widely and become problematic in many southwest Pacific islands and in the tropical north of Queensland, Australia (Benson 1992;Black 1984;Parsons and Cuthbertson 1992;Vitelli et al 2010). Being unpalatable, C. aromaticus provides very low feed value to cattle, which facilitates its spread in pastures (Vitelli et al 2010), where it can consequently establish a significant presence. Coupled with this invasion, the species can spread at an alarming rate across large areas within a short period of time.…”

“…Each seed head produces approximately 250 seeds, and C. aromaticus is capable of producing 450 to 550 million seeds ha −1 (Karan 1975). Studies conducted by Vitelli et al (2010) showed that soil seedbank densities of 44,400 to 56,700 viable seeds m −2 are present in areas of dense C. aromaticus infestation. Mature seeds are lightweight and are thus readily dispersed by wind over short distances.…”

“…Other vectors of dispersal include floodwaters (hydrochory), the hooves and digestive tract of cattle (zoochory), humans, and harvesting machinery. Cyperus aromaticus forms a persistent seedbank in which 31% seed viability was observed after 5 yr in seedbank-depletion studies (Vitelli et al 2010). Species like C. aromaticus form abundant and persistent seedbanks, and they are therefore able to germinate when conditions are favorable, reducing the possibility of local eradication and allowing them to maintain their population dominance (Pyšek and Richardson 2007).…”

Seletividade do halosulfuron-methyl aplicado em pré-emergência da cultura da mamoneira

“…Para esta espécie, o herbicida halosulfuron-methyl representa a principal opção, já tendo sido relatada sua seletividade por não resultar em redução no crescimento e promover fitotoxicidade à mamoneira, quando aplicado em pós-emergência (Silva et al, 2010). Este herbicida pertence ao grupo químico das sulfonilureias e possui, como mecanismo de ação, a inibição da enzima acetolactato sintase (ALS) e elevada eficácia de controle para espécies ciperáceas (Vitelli et al, 2010).…”

Seletividade do halosulfuron-methyl aplicado na dessecação antes da semeadura da cultura do algodoeiro

“…Outro herbicida do grupo das sulfonilureias com o mecanismo de ação de inibição da enzima acetolactato sintase (ALS), que apresenta elevada eficácia de controle para tiririca e outras ciperáceas, é o halosulfuron-methyl (Vitelli et al, 2010). Apesar disto, este herbicida está registrado para aplicação em pós-emergência somente na cultura da cana-de-açúcar (MAPA, 2013).…”