Weed Control 2007
In 2004,
2005 and 2006,
we released varieties of bugs to attack three specific
noxious weeds:
Leafy Spurge,
Musk Thistle and Canada Thistle.
Leafy spurge is one of the hardest to control,
as it is difficult to kill with herbicides and it spreads
easily.
Gary has marked 7 leafy spurge outbreaks on our property
with a GPS system and is checking the sites periodically to
track the progress of spurge spread or control.
One part of the monitoring process is to take panoramic
pictures of two sites where we do not use any other controls
(e.g.,
herbicides)
so we can compare them year to year.
Another part of the process is to visit the sites and try to
identify insects that are attacking the weeds.
This year,
we identified colonies of 3 of the 4 varieties we have
released specific to leafy spurge.
There are additional varieties of insects released by others
over the years that have found their way to our area.
It will take 5 or more years to determine if our new
varieties are able to control the weed.
Finally,
we use herbicides on 3 spurge sites near the Carriage House
and Main House in hopes of not having to look at noxious
weeds from our windows.
While spraying does seem to have reduced the density
(plants per square meter),
spurge still spreads through its deep and extensive root
system.
Thus,
the infested areas still increase in size.
(click on pictures to view larger version)
This gall caused by
Spurgia Esulae
inhibits seed production and weakens the spurge plant.
|
Oberea Erythrocephala
admiring her work
(note broken stem).
This insect lays an egg in the stem and the larvae eat
the plant from the inside.
|
Aphthona Nigriscutis
adults feed on leafy spurge foliage and flowers;
larvae feed on roots.
|
We found this caterpillar in
2004.
This insect was released in Bridger Canyon decades ago,
but it does not thrive well enough to be a factor.
|
Click beetle
found on spurge plant.
It must be lost since this beetle doesn't attack the plant.
|
Eggs laid by
Hyles Euphorbiae
(spurge hawkmoth)
on a spurge plant.
These will turn into caterpillars like the
ones pictured at far left.
|
More Weeds
We also released
Trichosirocalus Horridus
and
Rhinocyllus Conicus
for
Musk Thistle.
We recently observed these in their mating frenzy on newly
sprouted plants.
They have really helped control this weed.
Rhinocyllus Conicus is especially satisfying,
since we can take people on hikes,
spot a thistle,
break open the flower and show how larvae have eaten the
seeds.
Releases of
Urophora Cardui
and
Ceutorhynchus Litura
for
Canada Thistle
has helped a bit,
but the plant is difficult to control since it propagates
through its root system as well as by seeds.
The remaining noxious weed we would like to control is
Hound's Tongue,
but there are no insects approved for release in the United
States.
Some insects have been approved and released in Canada,
so perhaps they will eventually find their way here.
Gary takes frequent hikes with a
backpack sprayer
along game trails to kill hound's tongue.
Since the seeds spread primarily by attaching themselves to
animal's fur,
game trails are prime areas to pick up or drop off seeds.
We use herbicides to control these three weeds in disturbed
areas
(mostly along the driveway and the construction site).
We hope the insects can take care of the rest of the
thistles.
