St.
Johnswort (Hypericum perforatum):
Chemical
Control
Stem
& Leaves: This plant has many rust colored
stems. The stems are woody and may grow any where from 30-120
cm tall, (2-5ft). The leaves of this plant are oblong and/or
elliptic, they contain transparent glands, which produce an oil that
makes animals photosensitive. These leaves are attached to the
stem and the edges of the leaves contain tiny black dots. (Chadwick,
Kristen. http://mtwow.org/Hypericum-perforatum.html)
Flowers:
The flowers can be anywhere from 1 to 2 cm in diameter, they
are yellow and appear in clusters. Each flower consists of five
petals, with transparent black dots around the edges of
each.
The flowering period of St. Johnswort is May through September. This
flower also has a large amount of stamens. (Chadwick, Kristen.
http://mtwow.org/Hypericum-perforatum.html)
Roots:
The roots of this plant are an abbreviated
taproot system. The roots branch deeply into the earth, however some
of them do not and are shallow, these are usually the ones that
reproduce. (Chadwick, Kristen.
http://mtwow.org/Hypericum-perforatum.html)
Seeds:
The seed capsules of this plant are rounded at the end, and
they are about 5mm long. They are a rusty color and each contains
numerous seeds. They are brown in color and may be anywhere from 0.6
to 0.7 mm long. Each seed contains a germination inhibitor, but the
germination increases over time during rainy periods because the
inhibitor is washed off. (Chadwick, Kristen.
http://mtwow.org/Hypericum-perforatum.html)
Useful
Herbicides:
|
Herbicide Brand |
How to Apply |
When to Apply |
Active Ingredient |
Mode of Action |
|
Roundup |
broadcast |
September 15 to October 15 |
glyphosate |
growth regulator herbicide |
|
Tordon (picloram) |
broadcast |
September 15 to October 15 |
picloram acid present as a potassium salt |
growth regulator herbicide |
Note: Restrictions may apply depending on the Herbicide chosen.
Bibliography:
Montana War on Weeds Official Website. Chemical Control: Recommendation by weed. http://mtwow.org/chemical-control-by-weed.htm
Chadwick, Kristen. Weed ID: St. Johnswort (Hypericum perforatum). Montana War on Weeds. http://mtwow.org/Hypericum-perforatum.html
Created by: Stuart F. Date: 2/14/06.