When I walk the streets and trails of Cambria, I see weeds becoming heavily established in areas, which, as little as three years ago, were predominately grasses with minor weed infestations.
This fast weed expansion is another result of the drought. Although native grasses often compete well with these species, weeds can take over because they compete better in lower water regimes, bare soil and disturbed areas. The overrun of weeds may be a bigger danger to our visual characteristic wildland landscape at a pedestrian scale than loss of some overstory pines.
The weed species I see gaining in population most quickly are Italian thistle (Carduus pycnocephalus) and milk thistle (Silybum marianum). Both are native to the Mediterranean but have become widely established as common weeds in California and other countries according to the California Invasive Plant Council (IPC). The IPC tracks and monitors weeds, and its website illustrates its conclusions.
Both plants establish easily along roadside ditches and disturbed areas; they invade from the edges and spread out quickly. Both produce flowers that become seed heads and disperse seeds by wind. Seeds can persist in the ground for eight to 10 years. The live plants can grow up to 6 feet for Italian thistle and 9 feet or milk thistle. Dense weed clusters crowd out native plants and establish total control of small patches, which more quickly increases the rate of spread in the coming year.
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Italian thistle is a winter annual, and seed heads can germinate as early as October to December, after the rains start, and remain as late as June in this area with its low temperatures. A single plant can produce 20,000 seeds in one season. Seed dispersal averages about 75 feet from the plant but can be as much as 325 feet.
Blessed milkweed has been used as a medicinal herb for liver and bile functions but is not known to have any use in modern medicine. Root and leaves can also be used as human food if prepared correctly but are often toxic to livestock. Flowers/seed heads bloom from April through July.
Treatment, because of the different growth periods is complex. Selective chemical sprays do work on both when they are in active growth. Hand removal is easy for Italian thistle when the soil is soft and wet.
Hand removal of the milk thistle is difficult because of the root structure; although it pulls out, it must be removed/cut down to 4 inches below the soil, or it will grow back. Frequent mowing of either plant at time of flowering blooms before the seeds are released can help slow spread and reproduction.
However, frequent, or timely, cutting is not called for in the current weed-abatement plan (Cambria Community Services District Resolution 17-2016), which has primarily a fire-prevention goal, because the required cut date usually occurs after the weeds have released their seeds.
Where there are weeds, if we do not spray chemicals, at a minimum we need to cut weeds when they are blooming, possibly cutting areas with these weeds three times annually or at least twice, with the final cut earlier in the year (in May rather than July 22).
I suggest that we base the end date on the blooming period of target weeds (previously noted) instead of just the fire calendar. Concurrent goals of weed eradication and fire prevention could be addressed at the next Cambria weed regulations drafting.
Otherwise, I suggest a CCSD ordinance to control targeted noxious weeds by any means (cutting, botanical practices or chemical spray) on any property or community right of way in the CCSD’s jurisdiction.
If we do not quickly address uniform control of non-native noxious weeds, we will face a costly weed epidemic changing natural landscapes everywhere in Cambria. Solutions to contain and reduce weed expansion jurisdiction should eliminate weeds on all occupied, unattended and open space lands and roadsides within the CCSD.
Kermit Johansson is a retired landscape architect whose career included 36 years of service with the U.S. Forest Service. During his Forest Service career, he also worked in the logistical sections of fire teams based in Arizona and California.