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
Water Resources Manager ENSR
T:860-429-5323 ext 222