Are herbicides compatible with bio-control?
Yes and no. Each weed and beneficial insect has specific, case by case, situations where one can integrate herbicides and bio-control. For most cases, while herbicides may not kill the bio-control agents, the damage done to the host plants prevents the insects from completing their development. In other words, if all of the weeds die, then the insects won't have anything to live on.
To integrate insects with herbicides, we recommend first releasing insects on an area away from livestock, and that is not mowed or sprayed. Then, at least two years should be allowed for the insect populations in build up. If herbicides are to be used at all, it should be after these natural enemy populations have increased. Even then, timing of spraying is critical to minimizing the damage to the insect populations.
In a study which examined the combined use of the Black Dot Spurge Flea Beetle and the herbicides 2,4-D and picloram, North Dakota State University researchers found after two years ..."leafy spurge stem density was reduced 97% by the insect plus Fall applied herbicide treatment."
-Leafy Spurge News, 9/94
There are a variety of useful studies which illustrate the advantages and disadvantages of integrating biological and chemical weed control. Ask us about this. We can send you copies of studies which document this approach.
Biological Control of Weeds, Inc.
1418 Maple Drive Bozeman, MT 59715