The introduction and spread of exotic plant species is one of the most serious threats to biodiversity. It is estimated that over 40 million ha of U.S. land are already infested with invasive plants. Purple loosestrife is one such species that is currently invading wetlands and waterways in Midwestern states including 5,000 ha in Nebraska. Field studies were conducted in 2000 and 2001 at two locations in each year with the primary objective to evaluate performance of a single application of 16 herbicide treatments. A secondary objective was to document the impact of those herbicides on the total ground cover of local vegetation for two seasons after herbicide application. Evaluation at 10 wk after treatment showed that excellent season-long control (≥90%) of purple loosestrife was achieved with glyphosate at 3.36 kg ae/ha; 2,4-D dimethylamine at 2.66 kg ae/ha; triclopyr at 2.1 kg ae/ha; imazapyr at 1.68 kg ae/ha; and with the two mixtures of 2,4-D plus triclopyr at 1.33 1.26 kg/ha and 2,4-D plus metsulfuron at 1.33 ae/ha 0.042 kg ai/ha. Evaluation at 1 yr after treatment (YAT) showed excellent control (≥90%), with imazapyr at 0.33, 0.66, 1.12, and 1.68 kg/ha and metsulfuron at 0.084 and 0.168 kg/ha. Evaluation at 2 YAT suggested that excellent control (≥90%) was achieved with imazapyr at 1.12 and 1.68 kg/ha and metsulfuron at 0.084 and 0.168 kg/ ha. High rates of imazapyr caused negative effects on the local vegetation, indicating that use of these rates should be limited. Results suggest that a single application of more than half of the tested herbicides did not provide satisfactory control of purple loosestrife that lasts more than two seasons. However, the selective herbicides integrated with other control methods (e.g., mechanical, biocontrol) may be a valuable strategy for longer term control. Further studies are needed to evaluate the long-term effects of multiyear herbicide applications.
Nomenclature: 2,4-D; glyphosate; imazapyr; metsulfuron; triclopyr; purple loosestrife, Lythrum salicaria L. #3 LYTSA.
Additional index words: Integrated weed management, invasive species, noxious weeds.
Abbreviations: WAT, weeks after treatment; YAT, years after treatment.
