Management of Hydrilla Dependant on Biotype, Experts Say

Homeowners, boaters, fisherman, and other recreational users deal with a familiar looking problem weed in water bodies from Florida to Maine.  A resident on a lake in New York State would likely call the whirled leafed invader the same as a farmer in the bayou.  Hydrilla,  a nasty invader throughout many water bodies of the United States may look similar across state lines, but researchers with the Aquatic Ecosystem Research Facility in Lewisville, TX show just how different the plant, and it’s subsequent management can be from one state to the next.Hydrilla vertcillata.  Photo Credit:  NCSU AWP

Hydrilla is most often associated with one of two biotypes in the United States, and those two biotypes couldn’t be more different than the other when it comes to the life cycle of the plant.  The dioecious biotype, most often found in the southern US,behaves most often as a perennial growing during the warm months yet keeping biomass around throughout the year.  On the other hand, the monoecious biotype tends to grow rapidly from structures known as turions produced the previous year.  During the warm growing months, the monoecious plants grow rapidly and produce new turions both along their axils (axillary turions) and deep in the sediment (subterranean turions or tubers).  During the colder months, monoecious plants die completely back demonstrating the life cycle of an annual plant.

Biotype distribution.  Figure Credit - Owens et al.

Biotype distribution. Figure Credit – Owens et al. 2010

Why might these differences mean so much to resource managers?  Well, these distinct differences in hydrilla biotypes make time for management A LOT different between the two.  For example, Owens et al. showed that monoecious hydrilla produced nearly three times more tubers than did dioecious during the same amount of time.  Furthermore, monoecious tubers began sprouting as early as February and continued through June while dioecious didn’t begin sprouting until well into the summer months.  Monooecious tubers were also noted to be smaller than dioecious, suggesting less carbohydrate reserves for extended dormancy.  There were also differences in the number of tubers which sprouted amongst each biotype.  Monoecious hydrilla exhibited a sprouting rate of 70-100% whereas dioecious sprouting were much more widely distributed (from 90% to as low as 10%).

Monoeciou hydrilla tubers.  Photo Crecit - NCSU AWCP

Monoeciou hydrilla tubers. Photo Credit – NCSU AWCP

Owens et al. suggest that these differences in hydrilla biotype life cycles can and will make all the difference when it comes to management of the plant.  In the past, research has hinged on the success of various management techniques including chemical control, however the precision timing of applications could mean much more to success in real world situations.  The early sprouting and production of new tubers in the monecious biotype suggests that early season applications with endothall products may be most applicable and prevent the production of the plants “insurance policy”, more tubers.  The scientists also conclude that targeting the sprouting tubers of the dioecious biotype may be much more difficult as sprouting is much more unpredictable.  Other means of control such as biologic control through insects are also affected by the biotype present.  For instance, the hydrellia fly is most likely an ineffective means for controlling monoecious hydrilla because the plant does not persist throughout the life cycle of the insect (i.e. no plant material in winter!).

Topped out monoecious hydrilla in NC.  Photo Credit - NCSU AWCP

For those dealing with hydrilla in their lake, pond, or reservoir, your State’s location along the Mason-Dixon (or actually a little further south to the line between North Carolina and South Carolina) may make all the difference when it comes to taming the submersed menace.  To read the article in its entirety, click here.

For more general hydrilla information, click here.

For more information on monoecious hydrilla, click here.

To learn more about the Aquatic Plant Management Society, or to become a member, please visit our website at

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The APMS Blog is prepared by Dr. Brett Hartis, NC State University









This entry was posted in APMS Blog, endothal, hydrilla, weed control.