DOVER - The deep drawdown of Lake Pend Oreille last winter helped curb Eurasian milfoil growth, according to the Idaho State Department of Agriculture.

"In the shallow-water areas, we're not going to have major milfoil issues this year. It looks like the drawdown was a pretty effective winter kill with that cold snap we had early on," Tom Woolf, an aquatic plants program manager ISDA, told the Idaho Lakes Commission earlier this month.

The only exception to that trend was Boyer Slough, where influence from groundwater kept sediments from freezing.

A survey of the slough is planned for July and Woolf said a treatment project could be developed.

"At this point in time, it's just Boyer Slough that's on our watch list. Other places may be added to the list," said Woolf, who encourages the public to contact him if other problem areas are identified.

Although shoreline areas are not expected to be as infested with Eurasian milfoil as they have in the past, Woolf said there will likely be abundant growth of native plants due to the sunny and mild spring.

ISDA is also investigating the hybridization of native and exotic milfoil in Lake Pend Oreille. Hybrid milfoil has also been found in Cocolalla and Hayden lakes, in addition to Lake Coeur d'Alene.

"The hybrid milfoil exhibits more resistance to herbicide treatments. It's more difficult to control," said Woolf.

Woolf said the department is engaging in research to identify the various types of hybrids and investigate control methods.

Flowering rush, meanwhile, continues its aggressive march through the Pend Oreille system. It's now found below Albeni Falls Dam and in Canada, according to ISDA.

Flowering rush, a European plant believed to have entered the U.S. via the ornamental pond trade, has proved problematic to treat. Aquatic herbicide treatments have not proven effective and Woolf said there is 60 percent regrowth in areas where the plants have been pulled by hand.

"It's too widely distributed to talk about eradication," said Woolf.

However, one treatment method advanced by Bonner County is showing a great deal of promise. The county has been doing dry-ground treatment of the plants and there is anecdotal evidence that the method is effective.

To drill down on the effectiveness of dry-ground herbicide treatments, the county, U.S. Army Corps of Engineers, the Agriculture Research Service and ISDA are cooperating on a project to quantify the biomass and the impact of the treatment method.

"Up until this point, there really hasn't been an effective way to treat flowering rush, so this is an exciting innovation if we can find a new way to treat this stuff," Woolf said.