Basics of HYDRILLA Hydrilla (hydrilla verticillata) was discovered in Manitou during a routine weed survey in August
2006. The DNR is taking aggressive action to prevent to spread of this noxious, invasive weed. Hydrilla has groupings
of five leaves and each leaf as a serrated edge. Hydrilla can grow at far lower light conditions than other submersed
aquatic plants. This low light tolerance allows hydrilla to colonize deeper waters that have traditionally been weed
-free. Hydrilla can reproduce by four different methods: seed, fragmentation, turions, and tubers. Seeds are a very
minor form of the plant's reproduction. Fragmentation is a method of long distance dispersal. Just a half-inch sprig of
hydrilla transferred to another body of water can form a new population. Turions are dormant buds that form on the
stems of the plant and then drop to the sediment. Tubers and turions can remain dormant in the sediment for a few
years before germinating. If left unchecked, hydrilla can displace native aquatic plants, change the ecosystem,
reduce recreational opportunities, and cause property values to drop. For all these reasons, hydrilla has been
declared a federal noxious aquatic plant. For more information see:
http://www.in.gov/dnr/invasivespecies/LAKE_MANITOU_HYDRILLA_FAQ.pdf DNR plan for Hydrilla control on Manitou
The DNR in agreement with the LMA closed (cables and locks) all access ramps to Manitou on October 1, 2006. This
aggressive action was deemed necessary to prevent the spread of hydrilla to other bodies of water. In addition, the
DNR has inspected all lakes with public access within approximately one-half hour of Rochester and has not detected
hydrilla. In mid-September, 20 acres of Lake Manitou were treated with Komeen (chelated copper) and very good
results were observed.. At the time of the application, the two areas treated (city ramp/dam and behind Poet's Point)
were the most heavily infested areas the DNR had discovered. With treatment near the dam the DNR hoped to
reduce fragments flowing over the dam and infesting waters downstream. Since that treatment, DNR and LMA
inspections have found more areas of dense hydrilla and many scattered plants in the lake's northern basin. With
sufficient funding, DNR plans a more extensive program for 2007 and beyond. There could be more Komeen used,
but fluridone (Sonar) will be the "work horse" herbicide used. The plan is to maintain at least 6ppb of fluridone in the
lake for at least 180 days then repeating the treatment for multiple years until the tuber population is depleted.
Hydrilla is very easy to kill with a low dose of fluridone so much of the native vegetation should remain healthy.
Unfortunately, fluridone does not have an effect on the dormant tubers lying in the sediment. Therefore, to achieve
complete eradication, multiple years of fluridone treatment is necessary to kill the plant material as the tubers sprout.
The DNR plans include intensive sampling throughout the project to monitor for hydrilla tubers.
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HYDRILLA
HYDRILLA