Weed Control News

Integrating Chemical and Biological Control Against Purple Loosestrife

Purple loosestrife is an aggressive weed that is difficult to control. Herbicides are often used to reduce populations quickly, but this does not eliminate the problem. By integrating the leaf-feeding beetle Galerucella calmariensis with the herbicide glyphosate, there is potential to achieve both immediate and sustained control of purple loosestrife. 

The compatibility of glyphosate with the oviposition and survival of adult G. calmariensis and on the ability of G. calmariensis third instar larvae to pupate to adults was examined in field tests. Glyphosate (formulated as Roundup®) at a concentration of 2% and 4% solution had no impact on the ability of beetle larvae to pupate to new generation adults. To examine the effect of a 2% solution of glyphosate on oviposition and adult survival, adults were randomly divided between a direct contact group (adults sprayed directly), an indirect contact group (host plants with adults were sprayed), and a control group. Glyphosate did not affect G. calmariensis oviposition or adult survival. The results of this study indicate that G. calmariensis is compatible with glyphosate indicating that further field studies examining integrated control strategies for purple loosestrife are warranted.

Source:

Lindgren, C. J., T. S. Gabor and H. R. Murkin. 1999. Compatibility of glyphosate with Galerucella calmariensis; a biological control agent for purple loosestrife (Lythrum salicaria). J. Aquatic Plant Manag. 37: 44-48.

Bud Gall Fly for Biocontrol of Melaleuca

Melaleuca is an aggressive, invasive weed that is displacing native vegetation in Florida's Everglades at a rate of about 15 acres a day. This tree is native to Australia, but isn't a problem there. USDA and Australian scientists surveyed melaleuca trees at numerous sites in the tree's primary native range along the eastern Australian coastline in search of plant-feeing insects that could be potential biological control agents.  

One promising insect is a tiny, golden-brown fly they're calling the melaleuca bud gall fly (Fergusonina sp.). Working with a University of Florida colleague, the biology of this fly was extensively studied and now the fly is being shipped to a quarantine facility in Florida for final tests. The female fly deposits her eggs in melaleuca's growing tips, or buds. Melaleuca responds by forming pink, marble-sized galls in the buds. Inside the gall, the maggot develops into an adult, then emerges to start a new generation. Galled tips won't form new flowers that would otherwise produce vital seed. Host range studies indicate the fly is unlikely to attack other vegetation.

More than 8,000 freshly harvested melaleuca galls, with the fly inside, have been shipped to Florida for further study with other plant species. If the fly passes those tests, scientists will likely seek federal and state approvals to release it at melaleuca-infested sites. The fly would complement the work of the melaleuca leaf weevil, Oxyops vitiosa, released in Florida in 1997 after similar research in Australia and the United States.

Source:

Wood, M. 2000. Aussie insect may help fight melaleuca menace. USDA-ARS News Release, October 17,2000.


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