What is with all the dead trees?

In many cases, the trees are not dead, but defoliated by tamarisk leaf beetles. Defoliated trees look different from dead trees.

More about Bio-control

Link to Power Point presentation by Dr. Dan Bean
Link to Tamarisk Coalition April 2007 newsletter featuring beetles

Tamarisk Leaf Beetles in the San Juan Watershed
by Levi Jamison

Scientific name: Diorhabda elongata
Family: Chrysomelidae

What they look like
Adults are about the size of ladybugs; they are straw colored with two black stripes down their backs.
Larvae look like small black caterpillars; in their later stages, they have yellow stripes along their sides.
Eggs are pinkish tan and spherical; they are laid in clusters – up to 700 eggs in a lifetime (~one month).

Where they are from and where they are now

Tamarisk leaf beetles were introduced to the United States as a biological control of tamarisk. Originally discovered in the 1980s in Kazakhstan and China, beetles were extensively researched for over a decade in labs to assess safety and efficacy of their use within the USA.

Beetles can move over 100 miles in a single season. In 2006, tamarisk leaf beetles were introduced into the northwest portion of the San Juan Watershed (in southeastern Utah). Since then, beetles have been released at nearly a dozen sites along the San Juan River and its tributaries in Utah and Colorado. These beetles are adapted to the latitude of their home (around 43º N); in the San Juan Basin, they are physiologically “tricked” into over-wintering earlier in the year by shorter day lengths of the southern latitudes. This can cause pre-mature diapause, causing beetles to climb into the leaf litter and hibernate for the winter when tamarisk is still active.

What beetles do to tamarisk

Tamarisk leaf beetles suppress tamarisk through defoliation of the plants’ leaves, which inhibits growth as well as production of flowers and seeds. The beetles amass in large groups on trees, where females lay eggs near the tips of branches. When beetle larvae hatch, they eat the leaves, transforming a strong green tamarisk into a dead-looking brown tree in as little as a week. As beetles become established in an area, thousands of acres of tamarisk can be defoliated over a summer. Most of the growing season is destroyed for tamarisk as its leaves are demolished by hungry beetle larvae from June until September. Repeated defoliations over several years eventually lead to mortality as trees loose their tenacity and run out of root reserves.

Why are they used to control tamarisk

Self-sustaining beetle populations may be a cost effective tool to control tamarisk throughout the west, especially where tamarisk trees are difficult to reach. It is difficult to predict how well beetles will do further south.