Hydrilla is a noxious weed native, we think to Asia, although it has
spread widely across the globe today. This plant has leaves in whorls
of normally 5. It has serrations or small spines on the midrib, of which
is also slightly reddish when fresh.
Hydrilla is considered the most problematic aquatic plant in the United
states. Part of the reason for this is because of its fast growth and
its ability to regenerate from tubers and from fragments.
is a plant that looks very similar to three other invasive plants - Egeria
densa and Elodea canadensis. There
are however some easy ways to tell the difference. First of all, Egeria
has the largest leaves of any of them, growing up to 1/2 inch in diameter
and 3/4 to 5/4 inches long. Unlike Elodea, which is much smaller and has
whorls of 3 (rarely 4), Egeria has whorls of from 4-6, but never 3. Hydrilla
usually has whorls of 5. Finally, while Elodea and Egeria have smooth
leaves, Hydrilla's feels rough to the touch. This is because there are
small teeth on the midrib. With this information, you should be able to
distinguish these three major noxious aquatic plants.
Rob Nelson: "For three years I worked at an aquatic
plant research facility in North Texas (LAERF).
I worked as a researcher, trying to help understand both how native systems
are effected by invasive plants and how to control the spread of these
invaders. Probably the worst aquatic plant we had to deal with was Hydrilla.
Hydrilla can withstand a drawdown (no water in a pond) for several years,
it can withstand intense heat, and its impossible to get rid of by mechanical
extraction alone. We tried chemical means, which unfortunately kill the
natives as well. We finally tried to examine biocontrol as a viable option
to reduce plant stock."
"For several years, different controlled, and isolated experiments
on Hydrilla were conducted with an introduced fly from Pakistan. This
fly had larvae the drilled into the hydrilla stems and essentially caused
the entire plant to be so severely disabled that it could no longer compete
with natives species."
"Today the research that has been done through the Army Corp of
Engineers in Lewisville and in Vicksburg Mississippi has concluded that
there is no danger to native populations, and because of that the fly
has been introduced to several lakes and rivers. One of the best examples
of this is the infestation of the Rio Grande River, which has now been