WeedManagement

Weed Management

Hydrilla is widespread throughout Lake Pinehurst. (See ‘Weed Pictures’
on the Website.) It is growing around the entire perimeter of the lake
and in the depths of the lake up to 30 feet deep. Hydrilla is not native to
North Carolina, so it was brought to Lake Pinehurst by a boat that had
been in hydrilla-infested waters somewhere else. We first discovered
hydrilla in August 2008. We had the North Carolina Division of Water
Resources survey our lake, verify the level of hydrilla in the lake, and
develop a management plan specifically for Lake Pinehurst.

The control of hydrilla in Lake Pinehurst is feasible and this is the primary
objective of our annual aquatic weed management program. The control
of hydrilla will not be successful without the participation of all the
owners and properties around the lake. If we are not able to control the
hydrilla, it will spread across the entire lake and produce dense hydrilla
mats across the surface of the lake. These hydrilla mats will “kill” the
lake. There will be no boating, fishing or swimming. The irrigation intake
pipes in the lake will be clogged and irrigation from the lake will not be
possible. These hydrilla mats will become a breeding habitat for
mosquitoes and other pests. No one will want to live on a lake infested
with hydrilla and property values will drop dramatically.

We have formed an equal partnership with the Pinehurst Resort to
address this problem, including sharing the expense to control the
hydrilla. Our plan has been to increase non-reproducing grass carp by
1,000 in 2009 and 1,000 in 2010 and then maintain this level. Carp eat
their body-weight in hydrilla every day and are the most cost-effective
method of controlling the hydrilla. In addition to the carp, we are
treating the entire perimeter of the lake (28,600 feet) with a contact
herbicide in July and October to keep docks and shoreline clear of
hydrilla. Untreated areas will continue to spread to the rest of the lake.
Success requires the participation of every property owner around Lake
Pinehurst. We also perform spot treatments of hydrilla when required.

There are additional noxious aquatic weeds in Lake Pinehurst other than
hydrilla. Our contractor, North Carolina Lake Management, Inc., inspects
the lake at least every month of the year and treats the perimeter of the
lake for these other noxious aquatic weeds twice a month during the
active growth season.

Controlling Hydrilla

Controlling the hydrilla infestation with herbicides is very difficult and
costly. A two-pronged aquatic weed management approach that
incorporates the use of biological control (i.e. grass-eating carp) and
chemical control (i.e., herbicides) has been selected, and it will provide
relief of this noxious aquatic weed in a cost effective manner. This
approach was developed for Lake Pinehurst by the North Carolina Division
of Water Resources. Hydrilla has become a real danger to the lakes and
ponds of North Carolina and the state has an aggressive program in place
to help communities control or eradicate hydrilla in all infested waters.

Biological control was initiated by stocking the lake with 1,000 triploid
grass carp in the spring of 2009. Using grass carp has proven to be a
highly effective method of controlling hydrilla in North Carolina waters.
Immediate results were not expected, but we have seen evidence that the
carp are beginning to reduce the hydrilla in the lake. A significant
reduction in the amount of hydrilla is not usually seen until the second or
third growing season. A stocking density of 12 to 15 fish per vegetated
acre is sufficient to deplete hydrilla from a typical lake in North Carolina.
Our plan is to stock 2,000 carp in our 200 acre lake, which is about 15
fish per vegetated acre. The second 1,000 fish were added in April of
2010. Starting in 2011, we plan to stock the lake with about 200 grass
carp each year. It is best to stock carp over multiple years so as to create
a resident population comprised of multiple year-classes (cohorts). Prior
to stocking the lake with the carp, a permit to release triploid grass carp
is required. The NC Wildlife Resources Commission is the regulatory
authority and issues the permits.

Subsequent stockings, after the initial 2,000 carp, are determined by the
results of year-end surveys of vegetation and factoring in a normal
annual attrition rate for the carp. Supplemental stockings (years 3 and
after) should be made to retain the density of 12-15 carp per vegetated
acre until hydrilla no longer appears in the year-end lake surveys.

In addition to the biological control of hydrilla in Lake Pinehurst, we
added two hydrilla herbicide treatments (chemical control) to our annual
aquatic weed management program. These treatments are around the
entire perimeter of the lake and are needed to keep docks, waterways,
and irrigation pipes free of hydrilla. The chemical control is effective in
water up to seven feet deep. Twice each growing season, the hydrilla is
treated with a herbicide known as “diquat.” It is not harmful to fish or
humans, but it does require an irrigation restriction of about seven days.
The properties around the lake are notified prior to any applications of
herbicides requiring irrigation restrictions. Additional spot treatments to
highly infested areas may be performed on an as needed basis. As the
carp begin to reduce the hydrilla, it is our hope that the chemical control
of hydrilla can be reduced to a single treatment each year and then to
spot treatments when needed.

Depleting the hydrilla tuber bank is absolutely necessary and is the final
step in a hydrilla control/eradication program. The subterranean tubers
produced by hydrilla can remain viable yet dormant in the lake bottom for
several years. Retaining a resident population of grass carp is the most
economical method of depleting tuber banks in large ponds and lakes.
Carp will only consume the vegetative growth once a tuber germinates.
All of the viable tubers must germinate in order to eradicate hydrilla.
This final step basically becomes a waiting game. For ten years after the
last year to observe hydrilla in the fall survey, a minimum density of 1to
2 carp per acre of tuber beds must be retained.

Aquatic Weeds Other Than Hydrilla

Our aquatic weed management program is active all year. From April
through November, our contractor visits the lake twice a month to both
inspect the lake and to apply the appropriate herbicides to the actively
growing aquatic weeds. In North Carolina, there are more than 60
different aquatic weeds. There are at least 20 different herbicides that
treat aquatic weeds. Not all grasses in the lake are weeds. Many grasses
are beneficial to the lake and are required to provide needed habitat to
the game fish in the lake. It is important to identify the aquatic weeds
that are present and to select the most appropriate herbicide(s). This
requires an experienced aquatic weed management firm. The weeds
(other than hydrilla) that must be treated include algae, egeria,
watermilfoil, salvinia, and parrotfeather. There may be a few others.

When treating the lake for these aquatic weeds, the contractor may not
be spraying the entire perimeter of the lake. These weeds may be visible
in some areas of the lake, but not be resident in other areas of the lake.
The treatments are only done on visible aquatic weeds that react to the
herbicide in use. Sometimes, visible aquatic weeds are not sprayed
because the herbicide in use may not be effective on these weeds. They
will be treated on a subsequent visit. It is important for the property
owner to monitor his/her dock and bulkhead and let the weed
management board member know if it appears that too many weeds still
exist.

Impact on Game Fish

There have been many concerns raised that the hydrilla control activities
are reducing the game fish in Lake Pinehurst. We are working with the
Pinehurst Resort to determine if these concerns are valid and to identify
the root cause of any reduction in game fish.

Here is what often happens when hydrilla infests a lake with game fish.
Initially, hydrilla (10% or less of the bottom surface) has a desirable
effect on sport fishing by providing food and habitat for forage fishes and
cover for large predators such as bass, which lurk at the edges of the
hydrilla mats. The hydrilla mats effectively concentrate game fish in an
easily accessible area and catch rates can be high. However, small
patches of hydrilla grow quickly and begin to cover both shallow areas
and depths up to 30 feet. Once hydrilla infestations become more
invasive (infestations that cover 25 to 30 percent of the lake bottom,
some reaching the surface and some staying submerged; we are well
beyond 50% of the bottom surface), the infestation eliminates fish
habitat, causes stunting, and reduces the number of game fish. Hydrilla
increases the population of small fish (bream, sun fish, etc.) and
decreases the number of large fish. The small fish become overcrowded
and stunted because the hydrilla prevents the bass from reaching and
reducing the smaller fish. In the long run, hydrilla destroys the lake as a
fishery. We believe it is the hydrilla infestation that is the cause of the
changing fish population in Lake Pinehurst, not the annual management
program to get the hydrilla under control. In fact, our weed management
program is required to maintain Lake Pinehurst as an excellent fishery.

We will not know the real reason for the changes in fish catch in Lake
Pinehurst until we conduct a thorough "water quality assessment" that
should provide much better insight into what is really happening in our
lake. We do know that hydrilla, left unmanaged, will consume Lake
Pinehurst and eliminate all recreational aspects of the lake and will also
substantially reduce the property values around the lake. No one wants
this to happen.

I welcome your thoughts on our aquatic weed management program. It
is a fundamental component of our LPA mission to protect and preserve
the health and beauty of Lake Pinehurst.

You can email me at wreedy1@nc.rr.com.

Tom Reedy
President, Lake Pinehurst Association