Friday, April 13, 2012

Biological Control of Weeds

Insects attack weeds as well as our food and ornamental crops.  Weeds get diseases, too.  As early as the turn of the century, biologists have traveled the globe looking for bugs and disease that would be effective in destroying weeds.  These agents usually won’t wipe out the pest completely, but hopefully they can severely diminish the population so the weeds are no longer a problem. 

As early as 1930, workers at Parker Rancher were concerned with a cactus that was spreading in their pasture land at an alarming rate, covering some areas almost solidly. Over the years, a number of insects were introduced that biologists thought had the potential to destroy the cactus.  Finally, through evaluations that were conducted over a ten year period, it was found that an introduced moth and scale insect were able to either partially or completely eliminate the cacti.

Another weed, lantana, was a concern to ranchers because it was quickly encroaching onto pasture lands and displacing valuable forage grasses.  In 1902, biologist went to Mexico looking for insects that would feed on this weed. After importing and releasing many different insects, partial to substantial control was attained.   

Obviously, it’s a long process.   First, an efficient pest of the weed must be found. Second, after the potential pest is imported, there is an evaluation of the effectiveness of the agent as well as its risk to other plants.  The most promising agents are brought into a secure quarantine facility where they are carefully tested for potential impacts on native plants as well as economically important ones. They are also screened to eliminate any parasites that may be hitch hiking a ride.  After many years of evaluation, the weed pest may finally be introduced into its new environment.

Today, scientists are still looking for bugs and diseases that would safely keep our weeds in check; eradication is unlikely. In general, the biocontrol agents will only reduce the rate of spread and the abundance of the weed.