EURASIAN WATERMILFOIL

Case Study # EURASIAN WATERMILFOIL Myriophyllum spicatum

Scientific Name Myriophyllum spicatum • Native To Eurasia (hint used in part of the common name) • Date of U.S. Introduction Approx. 1990 • Means of Introduction Aquarium trade • Impact Crowds out native species Quick Facts

Umm....what is it? • Both native and non-native species are easy to spot because of their leaf arrangement, which is in a whorl. • Eurasian Watermilfoil can be identified easily because it typically has 12 to 21 pairs of leaflets, and native aquatic plant sepcies have 5 to 9 pairs of leaflets. Leaflet arrangement

Different arrangement for Eurasian watermilfoil

The Eurasian watermilfoil it is a very attractive plant with feathery underwater foliage. • However before it was invading our lakes it was commonly sold as an aquarium plant. • Many believe that it came here in the late 1800s, but it really did not start to show up until the 1940s in the eastern United States. • Throughout nutrient-rich lakes it has the ability to form thick underwater stands of tangled stems and vast masses of vegetation can be found along the water’s surface.

Okay we know what it is......so where is it going? • It is already making its way throughout the United States and it does not look like there is any way of stopping it. • Between its arrival and 1999 it has invaded over hundred water bodies. • Right now, watermilfoil has already occurred in about thirty-three states east of the Mississippi River. There are other reports stating that it is now in Colorado. • However it is now also very common in the Chesapeake Bay, the tidal Potomac River, and in many areas in the reservoirs of the Tennessee Valley.

Home range of where the Eurasian Watermilfoil

This Exotic plant is doing damaged....but how? • It is doing a lot of damage to floating mats of vegetation within lakes, rivers, and other bodies of water • It is doing this by preventing light from penetration the native species of plants found there and impeding the water traffic. • With so many dense stands, the watermilfoil impacts many recreational uses like swimming, boating, and fishing. • There are areas that seem to be very dense where it obstructs industrial and power generation water intake systems.

Can it be controlled? • The only bad thing about how watermilfoil acts is that once it becomes well-established within the water way, it is very difficult or even impossible to remove. • The herbicide Sonar has had only limited effect. • There are other ways of trying to control this such as harvesting, underwater rottotiling, and even trying to use a diver dredging to get rid of it. Mechanical removal

What is being done about this? • Taking action quickly is a key factor in order to control the problem before it really gets out of hand. • The biggest way in order to control the problem is to get public awareness. Public awareness is necessary to remove weed fragments at different boat landings, a commitment which would help to protect native plant beds from getting infected. • Both aspects of monitoring and prevention are the most important steps with keeping it under control. • Boaters are told to check all equipment that is used in infested waters and to remove all aquatic vegetation upon leaving either the lake or river.

Anything else being done • For example, there are three different methods that the State Agencies have tried using infected areas to reduce the problem, including • Mechanical Control • Most common method for controlling this pest is mechanical cutters and harvesters • This method should only be used when the colonies have become widespread and that they are located offshore so that it is easy for them to function without tearing up the substrate • Depending on the growing season which varies on the state it might take several cuts to get them under control

However using these cutters can be very costly with the size of the acreage that you are trying to get under control • Commercial harvesters can cost anywhere between $30,000-$100,000 to actually use • Then there are those annual costs per hectare that can range form $350 to $4,000 for just the regular control and if you really need some help then contractors must be use. Are you willing to pay anywhere between $300 to $600 per acre per cut? • Even though it can get very expensive for large areas it is probably the best way of doing things. There is a major downsideto mechanical cutting and that is that milfoil can re-generate fromsmall pieces of the parent plant. Thus, cutting without removal can actually increase the density of the pest speciesin the impacted area!!!

The second way of controlling the Eurasian Watermilfoil is Chemical • Herbicides are not typically recommended because they could be disruptive to most aquatic plnats (non-target species) many of which are native plants and in declining numbers • Chemical control can also be very expensive, here it can get to be close to $250-$1,000 per acre and might have to be repeated every one to four years • A main concern is to keep most or all of the native vegetation alive in the treated area • Within Minnesota the herbicide that is most commonly used is 2-4-D which is only selective for dicots • It is most effective in the spring or fall, however native dicots can be damaged during this time period as well

Lastly is the method of biological control- the use of one biological agent against another, in this case insects • The use of insects to control watermilfoil is a rather new approach and is still in the experimental stage • There are three taxa that have been considered as control agents: Acentria ephemerella, Cricotopus myriophylli, and Euhrychiopsis lecontei • All of these have been used in both Minnesota and Wisconsin and can still be found there today

Acentriaephemerella • This moth of a caterpillar has been know to eat just about any species of aquatic macrophytes (large plants). However, some states, such as Florida, have chosen not to use this species as a biocontrol agent due to lack of host specificity • It has been in North America since the ’20s making its way westward and towards the midwest • The caterpillar has been associated with some of the milfoil declines but most native vegetation has remained stable

Cricotopus myriophylli • This is species is a midge (fly larvae) and has has been associated with the decline of milfoil in the Pacific Northwest • However, there have been some problems with mass rearing of this species as well as a general lack of funding for research • Because of its limited availability this species is not being effectively used at the present time.

Euhrychiopsis lecontei • This species is a weevil, which turns out to be probably the most promising agent. It is a naturally occurring species which is now being cultivated as a control agent. • It has already been lab tested and seems to effective • At four test sites in Minnesota Milfoil populations have decreased at a record rate of about 75% in just a year • Complete control is limited by the availability of “farm raised” individuals

EURASIAN WATERMILFOIL