The ineffectiveness of herbicide control methods over the past 30 years led to the belief that there has to be a better/alternative way...everything else seemed to be failing! Biological control had been untried and appeared to be ready for investigation; but it, too, would not be without its obstacles. Since biological control involves the use of another organism as a control mechanism, and since that other organism may not be native to this country, stiff federal regulations MUST be followed prior to releasing any potential biological control organism.

Two weevils (insects) were eventually identified in Europe that naturally attack these thistles in their native European fields. One weevil lays eggs in the flower buds and the other in the mid-rib of leaves; this second weevil later feeds in the crown tissues of rosettes. The result in both cases is a much weakened plant with few to no flowers and seeds, and a much decreased competitive ability to survive in the surrounding ecosystem. Another bonus is that the weevils do not attack the same part of the plant, and they attack different stages of the thistle life-cycle. Once the first weevil has attacked the plant in the rosette stage, the second weevil attacks the surviving plants in the flowering stage. Thus the two weevils complement one another....Of course some thistles remain undiscovered or else the species would die out, but the weevils keep them in check. Both weevils were eventually released into Virginia's landscape following extensive testing. Dr. Kok had to make certain that no other wild plants would be suitable hosts and he also had to determine if the weevils would survive our climate. The initial natural dispersal of the weevils was slow because there were so many thistles,....why should the weevils stray very far from the release site if there were lots of food! In fact, the VT work showed that it took almost 6 years for a weevil population to show up in Dublin after being released in Pulaski...and these two towns are right next to each other. By the mid-1980s, thistle populations within tests sites were reduced by 90% following introduction of weevils 5-10 years earlier.