“Stunting” Hydrilla – A Look at Growth Regulators

coffeeI fondly remember watching my dad drink coffee on Sunday morning while reading the paper.  As an inquisitive 4 year old, I wondered what this warm liquid that my dad so eagerly gulped tasted like.  So as he went for a second round of pancakes, I shot in for a quick sip.  The bitter taste of what could only be described by a pre-K as dirty feet soaked in oil made its way out of my mouth as fast as it went in.  While I sat and wondered why any sane person would drink such a retched drink, my dad quickly chimed in with “Son, that will most certainly stunt your growth!”.  Years later I do find myself wishing I was a little taller (if only I hadn’t taken that sip) yet I am often found sipping that same drink every morning on my way to work, which I (and likely many of you) now would describe as the “nectar of the gods”.  If coffee truly stunted your growth, I am sure many of us would never have made it past the frame of our toddler selves.  There are however, things in this world in which stunted growth would certainly solve a problem.  In the aquatic plant management field, stunting the growth of prolifically growing invasives would provide a great deal of relief to scientist, lake managers, and homeowners alike.  In 2012, a group of scientists took a look at just that:  Regulating the growth of a troublesome invader, Hydrilla using Plant growth regulators (PGRs).  Heather Theel,  Linda Nelson, and Chris Mudge, all of the US Army Engineer Research and Development Center in Vicksburg, MS, took a look at using various growth regulators and growth regulating herbicides to control the notoriously awful submersed weed.    The purpose of using PGRs to reduce hydrilla growth is to provide the benefits of weed control while also maintaining the vegetative structure which can be important to fish and invertebrates.


Photo Credit: NCSU AWCP

Theel and her colleagues investigated the effects if hydrilla exposure to flurprimidol, bensulfuron-methyl and imazamox to suppress growth  while also maintaining structure.  The group found that all three reduced hydrilla shoot length by anywhere from 46 to 69% while reducing habitat complexity by 93% on average.  Research show that higher habitat complexity (such as that observed in a monotipic stand of hydrilla) can result in poorer foraging ability of fish when compared to a native stand of plants (with lower complexity).    The flurprimidol treated plants produced similar stem numbers as the control, however the volume of hydrilla was approximately half of the control.  “Although approximately 95% of flurprimidol treated hydrilla stems were located in the lower half of the aquaria, shoot biomass remained similar to the control throughout the study” Theel says.

The findings of this research suggest that growth regulators or growth regulating herbicides can provide a means to control the “weediness” of a plant like hydrilla without compromising for habitat.  In fact, regulators such as those tested in this study can reduce habitat complexity to a point at which species using the stand of vegetation can benefit from such reductions.

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