Rooted, dense water weeds with slender stems and strap-like and pointed, whorly leaves - five leaves per whorl.
The Hydrilla weed has a lot going for it. It is a rooted plant but if its long stem is broken, the broken branches start an independent life as new plants, drawing nutrients directly from water until it can find access to the ground to put down new roots. The abandoned roots, meanwhile, will arrange for new shoots in short order, thanks to their tubers potato like features that store nutrients just in case. The weed is also not discriminative of where it can grow. It will thrive in a pond or ditch with a few inches of water as easily as in 20+ feet deep lakes. Its only requirement is that the water is reasonably clean. The Hydrilla weed is a perennial plant with multiple reproduction systems. Besides growth from stem fragments, the plant also produces small, surprisingly lovely white flowers at the water surface that develop seeds. The foliage of the plant will typically die after producing the seeds but the tuber roots survive through the seasons, sprouting new shoots every year to complement the seeds efforts. It is those tubers that are the secret weapon of the Hydrilla weed. They can remain viable for more than 4 years, quietly lying in wait underground if there is a water shortage problem. And when they finally burst into life, one tuber can produce as many as 6,000 new tubers. It is also not as light sensitive as other plants, with it ability to grow with only 5% light transmission even turbid water is not a problem.
Some animals eat Hydrilla weeds. Turtles, in particular, love the weed as do some species of pond snails and crayfish. Grass carp will munch through the weed. The dense foliage of the weed is also useful as shelter for aquatic animals such as fish, frogs, turtles and a multitude of insects.
But the sheer mass and incredible growth rate of the Hydrilla weeds means it is a huge nuisance almost everywhere it grows. The weed totally dominates its environment, making it near-impossible for other weeds to survive. Even the fish and other aquatic animals soon suffer from the suffocating mass of the foliage. It is in fact the most devastating weed in the United States and makes it virtually impossible to fish, navigate or swim in the water.
Not surprisingly, the Hydrilla is one of the most reseached weed as scientists try to figure a way to contain its destructive spread.
The usual weed control measures of physical removal by nets, rakes and mechanical systems is only partly successful with Hydrilla because remaining fragments continue growing at that incredible rate of an inch a day. Herbicides are also limited in effectiveness because this weed is very resilient and comes right back. The biological option, such as using grass carp is also used with varying effectiveness.A new arsenal in the fight against the Hydrilla weed is the Lake Bottom Blanket, a novel combination of the physical removal and biological techniques. The Blanket is a formulated polyethylene sheet that is about 10 feet wide and as long as required. The blanket is lowered into the water and with its weighting system it will pinning the weed down while leaving room for aquatic animals to swim freely below and above the blanket. It works by depriving the Hydrilla of access to sunlight. Now, since this beast is so resilient, you must cover large areas to accommodate the canopy effect this weed has, and increase the down time to 6 - 8 weeks. On average, the blanket totally destroys the weed's foliage within four weeks, but to effect the tubers you need additional time. Best practice is to overlap several blankets and make sure they are stretched tightly.
The Lake Bottom Blanket is our lead weed control product and has been approved for use by the DNRs and DEPs of California, Nevada, New York, Connecticut, Massachusetts and Washington. It has already been used in over 400 lakes in over 29 states.
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