Vegetation Management and Maintenance Plan - Watsonville ...

whipping is critical. However, local conditions require site inspections to determine the exact
timing. The initial weed whipping should occur soon after the thistle has bolted (the main stem
has risen from the basal leaf grouping) and during the period when the flower buds are forming,
but have not yet opened. As bull thistles flower later in the season than Italian and slender thistle,
the initial weed whipping for bull thistle may occur at a different time. However, it is likely that
the initial bull thistle treatment will correspond with a secondary treatment for the Italian and
slender thistle species. Additionally, for maximum effectiveness, as all thistles in an area do not
bolt at the exact same time, several sessions over a period of a couple weeks may be required. If
funding or labor availability is limited, the initial weed whipping should occur when the majority
of thistles have bolted and are creating buds. If the timing is correct, only one or two retreatments
should be necessary. A periodic inspection of the thistle sites will be required to
determine the number and timing of re-treatments. Any thistle flowers that have opened or about
to open should be bagged and removed from the site
Bristly ox-tongue - Bristly ox-tongue should be weed-whipped prior to flower opening and seed
formation, in the late spring (see Table 5). Bristly ox-tongue should be weed-whipped as close to
the ground as possible without causing erosion or causing damage to desirable plant species.
String heads should prove effective, except late in the season, although plastic blades provide
greater control. As bristly ox-tongues flower over a long period of time, periodic site inspections
should occur during the flowering cycle and multiple treatments are likely. Any flowers that have
opened should be bagged and removed from the site.
Poison hemlock - Weed-whipping is most efficient if it occurs after the stalk has formed and
before the flowers have opened. If weed whipping occurs after the flowers have opened, it should
occur prior to seed formation. If poison hemlock is weed-whipped after the flowers have opened,
the flower heads should be separated from the major mass of the stem and root and be bagged and
removed from the site.
Although string heads are effective in the spring and early summer, plastic blades may be
required later in the season. Repeated treatments will be required, as poison hemlock can have
large root reserves. In some locations, poison hemlock can grow year-round and may require
periodic site inspections, throughout the year. Multiple spring and fall mowing/weed-whipping
should be done at the lowest height possible, without disturbing the soil (approximately 2-3
inches, depending upon equipment).
As poison hemlock is an annual/biennial species, with seed viability of three or four years, the
mowing/whipping regime needs to occur intensively for 3-5 years. Weed-whipping plants that
have dropped their seed is of limited usefulness for control, as the plant dies after seeding. The
entire poison hemlock plant is toxic and all above ground biomass should be removed from site if
animals or people may eat it.
3.1.5 Solarization
There are two types of solarization used to control weeds. Within the VMMM project area, only
one type of solarization is applicable for weed management, due to factors such as cost and
human disturbance. Within the VMMM project area, solarization is a suitable treatment for
Kikuyu grass, Harding/canary grass and potentially, poison hemlock (Table 4). For these species,
a minimum thickness 10mm black plastic needs to be in place for one or more years to effectively
kill the plant/plant roots and the successional weed seeds. Additionally, treatment by solarization
may be suitable for isolated large patches of many other invasive weeds, depending on location,
slope and proximity to desirable native plants. The use of City-supplied 30mil landfill liner
Vegetation Management and Maintenance Manual
Draft 18 July 27, 2007