Monday, December 11, 2006

Assessment of wavyleaf thistle infestation and potential for biological control in the Texas Panhandle

Nagendra Babu Earle, NAGENDRA_63@YAHOO.CO.IN, West Texas A&M University, Division of Agriculture, P. O. Box 60998, Canyon, TX, Gerald J. Michels,, Texas A&M University, Entomology, 2301 Experiment Station Road, Bushland, TX, and Bonnie B. Pendleton,, West Texas A&M University, Division of Agriculture, P. O. Box 60998, Canyon, TX.

Wavyleaf thistle, Cirsium undulatum(Nutt Spreng), is a noxious weed in 42 states, including Texas. It is a recent invasive species in the Texas Panhandle because of vehicular traffic from northern states. This research emphasized biological control with the objectives of using Global Positioning System equipment and Geographic Information Systems software to develop distribution maps and a database of infestation by wavyleaf thistle in the Panhandle, assessing biological control potential, and assessing interaction among biological, chemical, and mechanical controls for wavyleaf thistle. Areas of infestation ranged from 1-10,000 m2 with an average of 36.8 m2, and the distance from highways ranged from 1-60 m with an average of 2.3 m in the Panhandle. No infestation occurred at the borders of states except between Texas and Oklahoma. In 2006 we conducted field experiments with the following treatments; the flower head weevil, Rhinocyllus conicus (Froehlich), the bumble flower beetle, Euphorbia inda (L.), mechanical (cutting to the bottom), chemical (Banvel @0.33lbs ai/acre) and a nontreated check. We concluded that the percentage damage to seeds caused by Rhinocyllus conicus, Euphorbia inda, and mechanical control were significantly greater than the nontreated check (P < 0.0001, lsd=3.92). A greater percentage of damage to seeds was observed for Euphorbia inda, followed by Rhinocyllus conicus and mechanical control. The percentage of damaged seeds did not differ significantly between chemical control and the check. R. conicus could be the best biological control agent because E. inda is a generalist herbivore and pest on sunflower.

Species 1: Asterales Asteraceae Cirsium undulatum (wavyleaf thistle, plains thistle)
Species 2: Coleoptera Curculionidae Rhinocyllus conicus (thistle flowerhead weevil)
Species 3: Coleoptera Curculionidae Trichosirocalus horridus (thistle rosette weevil, thistle crown weevil)