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In This Issue   Natural Enemies of Giant Reed (Arundo donax)  
  Director's Foreword 1
  Ecological Restoration 3
  Education 5
 
        Collections 8
        Field Notes 9
  Research 12
  15
  18
  20
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  The Santa Clara River represents one of the few remaining major waterways in southern California that retains the capacity to support well-developed riparian forests, but at the same time it is one of the systems most affected by invasion of the non-native weed, Arundo donax.  

 

    Tom Dudley and Adam Lambert      
  River systems in California depend on periodic natural disturbance, in the form of seasonal cycles of flood scouring, to encourage the development of native riparian woodlands. These woodlands can provide essential wildlife habitat, filter out pollutants that enter waterways, and ameliorate the impacts of flooding and wildfire. The Santa Clara River represents one of the few remaining major waterways in southern California that retains the capacity to support well-developed riparian forests, but at the same time it is one of the systems most affected by invasion of the non-native weed, Arundo donax. Also known as giant reed, this bamboo-like grass has overwhelmed native plants from well upstream of Santa Clarita down to the Santa Clara Estuary. Arundo has promoted destructive wildfires, its debris clogs riverbanks and beaches, and it is known to be very poor habitat for birds and other sensitive species. Many control efforts have been undertaken using various combinations of mechanical cutting and herbicide treatments. These can be effective if done right but are extraordinarily expensive, as well as disruptive, to nearby native habitat.  The results are generally temporary--the next floods distribute the fibrous rhizomes downstream where they re-grow if moisture is sufficient, and the problem repeats itself.  

Sampling Transportation
Alan Kirk, Tim Widmer (USDA European Biological Control Lab), and Dudley sampling for natural enemies of Arundo in Nepal, and using unusual field vehicle for transportation to study sites.

An alternative approach to weed management is the introduction of natural enemies (or herbivores) that feed on the plant in its region of origin, in this case a broad zone from the Mediterranean across to the Indian sub-continent. A collaborative program involving the USDA Agricultural Research Service and various universities is underway to find and develop such biocontrol agents. Overseas co-operators headed by Dr. Alan Kirk of the USDA European Biological Control Lab in France (photo) have identified a variety of organisms--a stem-boring wasp, several species of stem damaging fly larvae, and a rhizome-feeding scale insect--that inflict substantial damage to plants in Europe and appear to feed only on Arundo without undue risks to native grasses or economic plants. Just this year some of these insects were transferred to a quarantine lab in Texas under the direction of Dr. John Goolsby, so that their impacts, specificity to the target weed, and suitability for handling could be further tested.

At the same time, weed biocontrol now involves an exhaustive analysis of the environmental and economic impacts of a weed and the benefits resulting from its control, in order to justify future implementation of the biocontrol program. Part of this includes determining if organisms already in the infested environment can have effects on the weed. These existing “enemies” can be harnessed to do greater damage to the weed, in this case Arundo.
 
   
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