Use of physical blockers to control invasive red swamp crayfish in burrows

The red swamp crayfish Procambarus clarkii is native to the southeast United States
but has successfully invaded nearly every continent around the world. Although physical,
biological, and chemical controls are employed to reduce or eliminate populations
in open-water systems, terrestrial burrows provide a potential refuge from aquatic
control treatments. We conducted burrow trials to test whether two physical blocker
treatments would kill P. clarkii in their burrows. Bentonite clay (a sealing agent) and
expanding foam (an insulating sealant) were each applied to 37 crayfish burrows,
and 36 burrows served as treatment controls (i.e., 110 total burrows). Burrows were
excavated 48 hr after the application of the physical blockers to assess the status of
crayfish in treated and control burrows. There was 74% mortality of crayfish in
occupied burrows treated with bentonite clay, 62% in burrows treated with expanding
foam, and 6% mortality in control burrows. We believe bentonite clay should continue
to be field-tested; however, because expanding foam is toxic to aquatic organisms and
is expected to persist in the environment, we do not believe it is a suitable physical
blocker for the control of invasive crayfish in burrows. Bentonite clay applications
likely will not need permits, will mitigate damage to banks and levees caused by
burrowing crayfish, and can be used with other control agents such as pesticides.
However, the use of physical blockers may be limited at field sites that have burrows
with complex morphologies. We believe the use of bentonite clay to control invasive
crayfish in terrestrial burrows will provide resource managers with an effective tool
for their integrative pest management programs.