Since 1987, the Plant Protection Section has conducted biological and integrated control programs targeted at musk, plumeless, and Canada thistles. Musk thistle is now under complete biological control through the introduction and establishment of beneficial insects that feed on it, thereby saving farmers at least $3,000,000 every year.

Urophora solstitialis and later, a beetle, Psylloides chalcomera, are successful. Other programs are examining the impact of timed clipping treatments, use of the endemic pathogen Myrothecium verrucaria as a bioherbicide, and studies on population dynamics.

Canada thistle continues to plague Maryland fields, pastures, and rights-of-way despite the establishment of the following insects: Cassida rubiginosa, Ceutorhynchus litura, Cleonis piger, Rhinocyllus conicus, Urophora cardui, Larinus planus, and diseases: Puccinia punctiforms, and Pseudomonas syringae pv. tagetis. We are evaluating the use of competing vegetation along rights-of-way, as well as more specific herbicides.

Puccinia punctiformis rust on
Canada thistle
Ceutorhynchus litura, a stem miner
of Canada thistle