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Secondary Weed Infestations Possible After Successful Control of Tamarisk

LAWRENCE, Kansas – Land managers are gaining an upper hand against exotic tamarisk in the western U.S. thanks to beetles introduced to control the invasive plant. Unfortunately, though, a secondary challenge remains. Soil conditions that are associated with tamarisk-dominated sites may promote the growth of other invasive weeds.

Researchers writing in the journal Invasive Plant Science and Management say soil once dominated by tamarisk tends to be higher in nutrients, organic matter and salts than nearby soils. In addition, mechanical removal of dead or dying tamarisk can leave behind wood chips or other plant debris that impacts growing conditions.

To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, researchers conducted germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. They determined that two species native to the western U.S. – purple threeawn and sand dropseed – are able to grow in the soil left behind after tamarisk is removed but that the tamarisk–associated soil is more favorable for Russian knapweed and downy brome, two invasive herbaceous plants commonly found in the region.

“Since Russian knapweed and downy brome are likely to do well after tamarisk dieback, managers should be prepared for secondary invasion by these species if they are found nearby,” says Patrick Shafroth, Ph.D., a research ecologist with the U.S. Geological Survey.

Researchers recommend further experimentation, soil testing and assessment to determine which desirable native species to plant once tamarisk has been successfully controlled.

Full text of the article “Germination and Growth of Native and Invasive Plants on Soil Associated with Biological Control of Tamarisk (Tamarix spp.)” Invasive Plant Science and Management Vol. 9, Issue 4, October-December, 2016 is now available at: http://www.wssajournals.org/doi/full/10.1614/IPSM-D-16-00034.1.

About Invasive Plant Science and Management
Invasive Plant Science and Management is a journal of the Weed Science Society of America, a nonprofit scientific society focused on weeds and their impact on the environment.  The publication focuses on invasive plant species. To learn more, visit www.wssa.net.

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