Most of the extant research offers several suggestions or recommendations that many homeowners confronted with these critters are likely to find unacceptable, but it’s all we have.
The bottom line, therefore, is that we have very few tools left in the toolbox for crayfish control. Additionally, there is an abundance of evidence showing that unauthorized use of such chemical ‘home remedy’ applications creates potential risk of impaired plant growth, contamination of local water sources, and secondary hazard exposure to other organisms. Social media and internet sources continue to mention a variety of ‘remedies,’ but they are illegal under our pesticide regulations as there are no labeled applications for such use.
Given that, there are no chemical treatments of any type we can discuss with clients. Although some states have requested and received approval for an emergency 24(C) registration, no special registrations exist here in Virginia. Currently, here in Virginia, there is nothing registered with EPA as a repellent or a toxicant for use on the broad array of crayfish species. The hard reality we face is that there is very little we can offer in terms of viable solutions. So, we’re dealing primarily with people’s concern about appearance more than anything else. There actually is not much evidence in the scientific literature that crayfish cause significant damage to plants, as they tend to be detritus feeders and scavengers mostly, though some species are more carnivorous than herbivorous. The complaints we receive typically are not related to damage to vegetation, but to aesthetic concerns (i.e., the unsightly “chimneys” and soil mounds) and negative effects to lawn maintenance equipment (i.e., mowers being dulled after the blades hit these soils mounds). As you might suspect, crayfish need saturated conditions to survive, so, where you have naturally-occurring high water tables, where people over-water their lawn and artificially raise the water table, or in years of exceptional rainfall, we see conditions that are favorable to and thus attract crayfish colonies. In years of “normal” precipitation, my office might receive 1 or 2 requests a year about crayfish and associated lawn problems, but during very wet years, we are inundated with complaints from all across the state. Jim Parkhurst, Associate Professor of Wildlife Science and Extension Wildlife Specialist in the Department of Fish and Wildlife Conservation for an answer.