Effectiveness of Control Treatments on Young Saltcedar (Tamarix spp.) Plants

Abstract Preventing the establishment of saltcedar in new areas requires early detection and rapid response. However, it is unclear when saltcedar develops perennating tissue and which treatments are most efficacious for young plants. The effectiveness of mowing, herbicide, and fire treatments, alone and in combination, was evaluated on saltcedar plants grown from seed to 4, 8, and 12 wk age in 2011 and 6 and 12 wk age in 2012. Plants were clipped to 2 cm height or remained intact. Plants were then exposed to no treatment (control), herbicide application (0.12 mg ae imazapyr), or treated with fire for 30 or 60 s. Six weeks after treatment, plant survival and tallest living shoot height were recorded and roots were dried and weighed for biomass comparison. Saltcedar survival increased with greater plant age. No 4-wk-old plants survived herbicide or fire treatments, whereas 6-wk-old plants were eliminated by fire. Clipping alone did not control plants of any age but clipping before fire was the most effective control for older plants. Herbicide alone did not kill 8- and 12-wk-old plants during the study period, but reduced plant vigor suggests that these applications may be effective in the long-term. Fire alone for 60 s was the most effective single treatment for 12-wk-old plants. Root biomass was reduced for all treatments relative to untreated plants with the lowest biomass typically associated with fire treatments. Resprouts were shortest for combined clipping and herbicide and clipping and fire treatments. Results indicate that saltcedar grown from seed can develop viable belowground reproductive tissues between 6 and 8 wk after germination. Multiple intensive control practices may be required to kill saltcedar plants ≥8 wk of age, whereas younger plants can be controlled by single, less-intensive treatments such as fire. Nomenclature: Arsenal; imazapyr; saltcedar, Tamarix ramosissima Ledeb. TARA; T. chinensis Lour. TACH; Tamarix hybrids. Interpretive Summary: Early detection and rapid response is the primary campaign for managing weeds in the United States, yet little is known about the best method for controlling new saltcedar infestations. Older saltcedar individuals are often difficult to control because of the presence of belowground reproductive tissues but when these structures become viable is poorly understood. This research found that young saltcedar response to control treatments is dependent on plant age and treatment. All plants treated with clipping between 4 and 12 wk of age were able to recover and produce robust plants. Destructive treatments such as fire eliminated 4- and 6-wk-old plants but 8- and 12-wk plants often regrew vigorous shoots from belowground buds following complete top-kill by fire. These results suggest that belowground reproductive tissues can become viable between 6 and 8 wk of age. Fire and herbicide alone resulted in younger plant mortality and reduced growth for older saltcedar but the use of these practices will depend on land management options. Clipping prior to herbicide or fire treatment was the most effective control and could be used to treat small populations or individual plants. Fire may be preferred over herbicide application in areas where vegetation is adapted to this disturbance and burn programs are already established. On the other hand, herbicide may be desired where saltcedar density is high, there is minimal herbicide-susceptible native vegetation, and/or the landscape is unsuitable for burning or other mechanical removal methods. Spot fire treatment to individual plants, rather than a large-scale field burn, may be another control option although this technique has not been field-tested.