An integrated approach to salt cedar control and rehabilitation

Authors: Clements, Darin - Charlie; Harmon, Daniel - Dan; YOUNG, JAMES - US Department Of Agriculture (USDA); KNIGHT, JEFF - Nevada Department Of Agriculture

Submitted to: The Progressive Rancher
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2015
Publication Date: 5/4/2015
Citation: Clements, D.D., Harmon, D.N., Young, J.A., Knight, J. 2015. An integrated approach to salt cedar control and rehabilitation. The Progressive Rancher. 15(5):36-37.

Interpretive Summary: Salt cedar (Tamarix spp.), a small tree native to Central Asia has invaded more than 4.7 million acres in the western United States. Planted in the early 1800s as an ornamental and later for windbreaks and soil stabilization, it escaped cultivation, infesting riparian and adjacent communities. Salt cedar plants readily regenerate from crown and root sprouts following mechanical removal or burning of the aerial portions of the plant. Stream bank erosion can result in the transportation of stem or root fragments that may root and establish new infestations. The overwhelming means of spread of salt cedar is by seedling establishment, which is often promoted by flooding events that leave bare muddy ground or newly exposed river banks. In an effort to control salt cedar, the USDA-Agricultural Research Service investigated a number of potential control insects in the 1970s. By the 1990s a foreign leaf eating beetle (Diorhabda carinulata formerly D. elongata), was released by USDA. In 1999, the USDA, Agricultural Research Service, Great Basin Rangelands Research Unit constructed three bio-control quarantine cages in North-western Nevada. Vegetation monitoring began in May 2001 with salt cedar measurements of plant morphology of 100 marked trees [e.g. height, diameter, densiometer (percent), foliage/stem status (green, defoliated (dead leaf /stem), re-growth, and flowering]. We measured nearest shrub and primary vegetation under the canopy along with presence or absence of beetles. These measurements were taken (last week in May) from 2001 through 2011. After measuring defoliation for a decade, complete defoliation reached a high of 54% in 2004 at the Lovelock site and a high of 18% at the Walker site in 2007. By 2011, complete defoliation was recorded at 41% and 14%, respectfully. Salt cedar was removed with heavy equipment at the Lovelock site in 2008 that resulted in the sprouting of salt cedar whips from roots that averaged a density 7.3/m² with 47% cover. Various herbicides were applied in 2011 to test efficacy of salt cedar control and vegetation response. Polaris (Imazapyr) @ 1% rate recorded the best performance at 91% control while Garlon 3a @ 0.5% rate applied to whips recorded the lowest control at 22%. Initial understory response was very favorable in the Polaris plots as herbaceous vegetation increased from 17% cover to 44%. Seeding efforts with various species following herbicide applications also failed during extreme drought conditions, 2011-2014. Based on our observations we find it most probable that heavy equipment and herbicides will continue to be the tools that will ultimately aid in the salt cedar control efforts.

Technical Abstract: Salt cedar (Tamarix spp.), a small tree native to Central Asia has invaded more than 4.7 million acres in the western United States. Planted in the early 1800s as an ornamental and later for windbreaks and soil stabilization, it escaped cultivation, infesting riparian and adjacent communities. Three species primarily exist in northern Nevada, two are invasive (T. ramosissima and T. chenensis), and the other non-invasive (T.parviflora). They are visibly differentiated by flowering as the non-invasive T. parviflora flowers first before leaf bud break. There is considerable debate concerning why salt cedar is such a highly invasive species. It is not clear if salt cedar invasion is the cause of changes in riparian communities or a consequence of changes in stream hydrology. Regardless, the presence of salt cedar is associated with dramatic changes in geomorphology, ground water availability, soil chemistry, fire frequency, plant community composition, and wildlife diversity. Salt cedar plants readily regenerate from crown and root sprouts following mechanical removal or burning of the aerial portions of the plant. Stream bank erosion can result in the transportation of stem or root fragments that may root and establish new infestations. The overwhelming means of spread of salt cedar is by seedling establishment, which is often promoted by flooding events that leave bare muddy ground or newly exposed river banks (Figure 1). Seed production may exceed one half million seeds per plant during a single season. We have recorded salt cedar seed rain of 49,500 seeds per ft² in salt cedar infestations, 25,800 seeds per ft² 100 yards down-wind, and 550 seeds per ft² 4 miles down-wind from infestations. In an effort to control salt cedar, the USDA-Agricultural Research Service investigated a number of potential control insects in the 1970s. By the 1990s a foreign leaf eating beetle (Diorhabda carinulata formerly D. elongata), was released by USDA. In 1999, the USDA, Agricultural Research Service, Great Basin Rangelands Research Unit constructed three bio-control quarantine cages in North-western Nevada; Lovelock, Walker and Stillwater sites. In 2001, the leaf beetle was released. At two of the three release sites (Walker and Lovelock) the beetle initially established very well. Annual vegetation monitoring was conducted at the Lovelock and Walker release sites for 10 years. After measuring defoliation for a decade, complete defoliation reached a high of 54% in 2004 at the Lovelock site and a high of 18% at the Walker site in 2007. By 2011, complete defoliation was recorded at 41% and 14%, respectfully. In 2001 vegetation measurements at the Lovelock site recorded the occurrence of saltgrass (Distichlis spicata) in 47% of the quadrats with an average cover of 9.26%. Tall whitetop (Lepidium latifolium) was also present in 47% of the quadrats beneath the canopy with an average cover of 12.68%. By 2011 tall whitetop was not present in the quadrats and saltgrass had increased to a presence of 50% beneath the canopy with an average cover of 48.46%. The Walker site recorded much more vegetation diversity with numerous species present during favorable precipitation years and virtually nothing during drought periods. Initial vegetation monitoring in 2001 yielded cheatgrass (Bromus tectorum)and Tansy mustard (Descurainia pinnata) as the most frequently recorded species. Cheatgrass occurred in 42% of the quadrats with an average cover of 7.14%, while Tansy mustard was present in 19% of the quadrats with an average cover of 1.95%. By 2011 there had been a significant decrease in vegetation presence (2001 = 49% vs. 2011 = 2%) and average vegetation cover decreased as well (2001 = 5.38% vs. 2011 = 0.01%). Various herbicides were applied in 2011 to test efficacy of salt cedar control and vegetation response. Polaris (Imazapyr) @ 1% rate recorded the b