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Bio-Control
Biological control, or bio-control, is the intentional use of natural enemies to help control pests, including weeds like tamarisk.
The following information was compiled in part from Dr. Dan Bean’s publications:
Tamarisk has been able to flourish in North America in part due to the absence of natural predators. Two predators have been identified to help control tamarisk populations, tamarisk leaf beetles and goats.
The Tamarisk Leaf Beetle
Background
In the 1980’s the USDA began to look for insects that are natural enemies of tamarisk in China, Kazakhstan, Uzbekistan, Tunisia, Greece, and many other places where tamarisk is native. Similar programs using beetles as biological control agents have been successfully used before in North America for weed bio-control.
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They eventually decided on a tamarisk eating specialist called the
Tamarisk Leaf Beetle (Diorhabda elongata).
Once the Tamarisk Leaf Beetle was identified, the USDA began an extensive testing process. Dr. Andrew Norton, Professor of Pest Ecology and Management at Colorado State University stated: “The tamarisk leaf beetle has undergone more pre-release testing than any other biological control agent in U.S. history”. |
Testing of the tamarisk leaf beetle began in 1992. Approval to begin field testing was given in 1999 and the beetles were released in outdoor cages in research areas at 10 sites in 6 states (CA, NV, UT, CO, WY & TX). In 2001, the beetles were released into the wild.
Is the beetle safe for native plants?
Safety of native plants is one of the most important considerations of bio-control. The primary goal of bio-control safety testing is to determine if the beetle will feed exclusively on tamarisk. Tamarisk is in its own family, Tamaricaceae, which has no native North American members. Insects that specialize on tamarisk will not find similar plants among the native flora.
After the beetles were brought to the US they were maintained in USDA quarantine laboratories in Texas and California. The beetles were subjected to very extensive host range testing where they were offered a wide selection of native and crop plants.
The tests showed that the beetles favored tamarisk to native plants and would starve in search of a tamarisk. The only native affected by the beetles was the shrub Frankenia. Scientists found that larvae were able to feed on four North American species of Frankenia. Adult beetles were not attracted to and did not feed on Frankenia.
Additional field tests have shown that when the insects defoliate a tamarisk stand they seek out more tamarisk instead of looking for different food sources nearby.
How it works
The beetles control tamarisk by feeding in large numbers to defoliate the plant. Once the plant has been defoliated it can no longer photosynthesize and store food in its roots. Repeated defoliation over several years causes the root mass to decrease in size until it can no longer support the plant.
Studies suggest that a tamarisk tree can be killed within 3-5 years of beetle infestation. Time estimates vary depending on the size of the plant and its root mass, how often it’s defoliated, and the resilience of the individual plant.
Once the beetles significantly reduce the tamarisk population they will naturally decline in numbers. When an insect only feeds on one specific plant and when that plant population is reduced or eliminated, the population of that insect drops off dramatically.
Other sources
Milbrath, L.R. and C.J. DeLoach. 2005. Host specificity of different populations of the leaf beetle Diorhadba elongata (Coleoptera: Chrysomeldae), a biological control agent of Saltcedar (Tamarix spp.). Biological Control 36: 32-48.
Goats
Background
Goats can also be used as a form of biocontrol. Goats will feed on tamarisk shrubs if fencing limits other food sources. Typically, a guard dog, herding dog, and goat herder are required.Several private goat herds are available throughout the West but there is limited cost and success information. It is too early to provide good information on the effectiveness, applicability, and pros and cons of using goats as a viable means of controlling tamarisk. A large project is currently underway on the Rio Grande in New Mexico to provide this information.