Control of Variable Watermilfoil in Bashan Lake, CT with 2,4-D: Monitoring of Lake and Well Water.

Variable watermilfoil (Myriophyllum heterophyllum Michx.) has recently become a problem in Bashan Lake, East Haddam, CT, USA. By 1998, approximately 4 ha of the 110 ha lake was covered with variable watermilfoil. In 1999, the milfoil was spot treated with Aquacide®, an 18% active ingredient of the sodium salt of 2,4-D [(2,4-dichlorophenoxy) acetic acid], applied at a rate of 114 kg/ha. Aquacide® was used because labeling regarding domestic water intakes and irrigation limitations prevented the use of Navigate® or AquaKleen®, a 19% active ingredient of the butoxyethyl ester of 2,4-D. Variable watermilfoil was partially controlled in shallow protected coves but little control occurred in deeper more exposed locations. 2,4-D levels in the treatment sites were lower than desired and offsite dilution was rapid. In 2000, the United States Environmental Protection Agency (USEPA) issued a special local need (SLN) registration to allow the use of Navigate ® or AquaKleen® in lakes with potable and irrigation water intakes. Navigate® was applied at a rate of 227 kg/ha to the same areas as treated in 1999. An additional 2 ha of variable watermilfoil was treated with Navigate® in 2001, and 0.4 ha was treated in mid-September. Dilution of the 2,4-D ester formulation to untreated areas was slower than with the salt formulation. Concentrations of 2,4-D exceeded 1000 μg/ L in several lake water samples in 2000 but not 2001. Nearly all of the treated variable watermilfoil was controlled in both years. The mid-September treatment appeared as effective as the spring and early summer treatments. Testing of homeowner wells in all 3 years found no detectable levels of 2,4-D.(PDF contains 8 pages.)

The cost of quinine Cinchona pubescens control on Santa Cruz Island, Galapagos

We analyse the cost of controlling the invasive quinine tree Cinchona pubescens Vahl in the highlands of Santa Cruz Island, Galapagos. Control costs in ten 400 m2 plots formed the basis for estimating the cost of control over the whole island. In the plots, densities were 2100–24,000 stems/ha (stems >150 cm tall) and 55,000–138,000 stems/ha (all size classes combined). Control involved uprooting small plants, and applying of a mix of metsulfuron methyl and picloram to cut stumps or to machete cuts in the bark of larger trees. These methods are presently used by Galapagos National Park field crews to control quinine. Costs (in man hours, herbicide and US$) were related to stem density; the density of stems summed across four height classes was a better predictor of costs than density of any one size class. Regressions (on all size classes combined) formed the basis for predictive models of costs. Costs ranged from $14 to $2225 per ha depending on stem density. The amount of herbicide (active ingredient/ha) that must be applied to high density stands of quinine is higher than typical rates of application in an agricultural setting. The cost of treating all existing plants once across quinine’s known range on Santa Cruz Island (c. 11,000 ha) was estimated at c. US$1.65 million. CDF Contribution Number 1013.