Hydrilla in December?

     Over the past few weeks (during November and early December), a number of Lake Guntersville users and residents have reported long strands of hydrilla floating in mats. In some cases, these mats have impeded boating. At other times, the mats have floated to shore and blocked boathouses, boat ramps, and general lake access. Many have thought these might be cut or “harvested” stems of hydrilla. However, in all likelihood, this is not the case.

     According to Terry Goldsby, Senior Botanist with Aqua Services, Inc., all plants depend on photoperiod (day length) as the primary stimulus for most of their natural physiological processes. Many perennial species in temperate regions respond to shortened day length during autumn by entering “fall senescence”. Hydrilla is no exception. Just as deciduous trees drop their leaves in the fall, hydrilla releases many of its stem before overwintering.

     We know that hydrilla grows vigorously during the longer days of summer and often produces a tremendous volume of vegetative material (biomass). As day length shortens with the approach of autumn and the photoperiod is reduced; photosynthesis and growth slow, and hydrilla is unable to sustain maximum biomass. Fall senescence begins, and a natural response of the plant is to turn its energy from vegetative growth to subterranean tuber production. These tubers are the main regenerative mechanism of hydrilla that allow it to return each spring. Simultaneously, auxin (an important plant hormone) decreases. As auxin is exhausted, the hydrilla stems weaken and become susceptible to shearing from wind and waves, high flows, and other factors. The end result is a lot of floating stems and strands on the lake during late fall and early winter.