Many of you have undoubtedly heard and/or seen a small boat with a large “water cannon” sprayer on the front out on the waters of Lake Gaston and Kerr Lake. The “crew” have repeatedly jammed a large t-shaped pipe into the ground (seen above), pulling up endless amounts of mucky sediment as if searching for gold. However, it isn’t prospectors out looking for their own fortunes, but rather scientists assessing the current state of Hydrilla in various areas across the lake. As many of you undoubtedly know, the actual plant biomass is above the sediment so you may be asking yourselves; “Why in the world are they looking in the mud?” The answer to tracking hydrilla in the long term is actually all about the “mud”, or better put, what is IN the sediment.
As we have discussed in weeks past, the key to hydrilla’s survival from year to year has very little to do with the actual plant material itself. The key is actually all about tubers, the survival structures produced by hydrilla annually on its root system (See “The Dormant Demon: Why Hydrilla Tubers May Mean Control, Not Eradication”). It is actually these tubers, more specifically their numbers and how they are acting, that can tell us a lot about the success of a management plan. In last week’s article, we discussed a new approach to management on Lake Gaston specifically regarding the multiple year treatment of the same sites. So how exactly do we judge if we are going in the right direction with such a plan? The answer is tuber monitoring of course.
Assessing the number of tubers in an area is extremely important as it can give us an idea of how many “potential” plants we have lying dormant for the following years growing season. If tuber numbers are high in a given area, then that area more than likely needs continued management in future years. If tuber numbers are low, then that area could potentially be controlled by other means (grass carp, spot treatment, etc.) rather than an area wide treatment. Because we aren’t able to sample every square inch of an area, we rely on tuber sampling in an area about 3 feet across and 3 feet long at multiple sites in an area and extrapolate across the entire site. As we monitor tuber numbers in the spring and fall of each year, we are able to see what tubers are available to sprout before hydrilla begins growing, and more importantly, what is left over at the end of the growing season to start new growth the following year.
Also important in tuber monitoring is checking the sprouting rate of tubers in an area to be treated. If sprouting rates remain low, then tuber numbers are at levels substantial enough to regenerate a stand of hydrilla annually. If sprouting rates are high and remain high, then the plant is most likely requiring the majority of tubers annually for stand regeneration.
As we continue with our monitoring of tubers within long term treatment areas, tuber numbers and sprouting rate will let us know just how our plan is working, and more importantly, when we can potentially STOP treatment on those areas and let other factors take hold. Keeping tubers numbers low and sprouting rates high should pave the way for reducing hydrilla overall in legacy sites such as Lake Gaston. So the next time you see a group endlessly pulling up mud and washing it, you’ll know that the “tuber team” is working to reduce hydrilla in YOUR neighborhood.
Next time we will take a break from Hydrilla and talk a little about topics suggested by readers. If you have a topic request, question, etc. please email to bmhartis@ncsu.edu.
If you have questions please contact your Aquatic Extension Associate, Brett M. Hartis, at (919)-515-5648 or email at bmhartis@ncsu.edu.
