Variable leaf watermilfoil (VWM) and Cabomba caroliniana (CC) represent a very difficult combination.

 

They co-occur in coastal outwash lakes most often, with slightly acidic waters and usually sandy substrates overlain by organic muck.

Dominance can fluctuate by year or location in the pond, although under stable conditions, CC usually becomes dominant.

No one herbicide will kill both, and no one herbicide will kill either in a single dose.

Fluridone works best on CC, but only at >10 ppb, so death of a lot of natives is to be expected.

2,4-D works best on VWM, but can't be used in most situations where there are drinking water wells that could have a connection to the lake (as if often the case in sandy areas).

Benthic barriers will control both, but are very expensive on an areal basis and disrupt lake ecology if more than about 10% of the littoral zone is covered.

Handpulling is pretty much futile unless we are talking about a plant here and there, which is almost never the case.

Drawdown works on both if the target area can truly be dewatered and frozen for at least a month - this is getting harder to do with global warming, and the muck sediments often protect the plant root systems and allow considerable survival.

There are no known biocontrols for these species.

That leaves dredging, which carries high expense (~$15/ cu. yd.) and "collateral" damage.

will put the system back to what it was at some point in the past.

provides a lot of other benefits if it can be afforded and permitted

If we are talking about small (<20-50 acre) waterbodies, dredging would be my choice.

 

Kenneth J. Wagner, Ph.D., CLM (Certified Lake Manager)

President North American Lake Management Society (www.nalms.org)

Water Resources Manager ENSR

P.O. Box 506, 11 Phelps Way

Willington, CT 06279

T:860-429-5323 ext 222

F:860-429-5378