Yellow starthistle strong foe in weed management
If weeds are a hassle in front yard landscaping and back yard
gardens, imagine combating invasive weeds such as the yellow
starthistle countywide.
Yellow starthistle strong foe in weed management
If weeds are a hassle in front yard landscaping and back yard gardens, imagine combating invasive weeds such as the yellow starthistle countywide.
California agencies are working in Santa Clara and San Benito counties to fight invasive weeds – those that spread rapidly through landscapes, killing off native plants and harming other species – but have learned over the years that flexibility and partnership is key.
In Santa Clara, some of the groups involved in the partnership include the Santa Clara County Open Space Authority, the Santa Clara County Parks and the United States Department of Agriculture.
One of the most invasive weed species is yellow starthistle, a weed that starts out as a small, green succulent plant and ends up dried out and full of needle-like stickers. The plant is native to southern Europe, but has made a home for itself in Santa Clara and San Benito.
“In 1996, we broke the county up into a square mile grid,” said Eric Wylde, a supervising agricultural biologist with the county of Santa Clara. “Yellow starthistle was present in each.”
The weed is toxic to horses; its thorny thistles pop bicycle tires and the nettles sting passersby. It wreaks havoc on native plants and grasslands.
“They are a problem because of their ability to tap into water resources better than any other plant,” Wylde said. “When it first emerges it sends out tap roots. It looks like it hasn’t done much, but it can have a 4-foot root on a plant with just a few leaves.”
The native plants – which have a shallower root system – often die off in regions were yellow starthistle has invaded.
The methods used to fight yellow starthistle often depend on the location of the weed, which can be found in Santa Teresa County Park and Coyote Creek Parkway.
In more remote areas, controlled burning is one method that has been successful. The San Jose fire department and the county parks worked together a few weeks ago on a burn in Santa Teresa County Park.
“San Jose fire got to expose a crew to a live fire,” said Don Rocha, a County Parks supervisor. “We got to burn yellow, purple starthistle and barbed goat grass.”
Burns are most effective during the summer months when the plant is flowering and before it begins forming seeds. Fall burns come at the worst time, as they help to spread the seeds, according to Stuart Weiss, an ecologist working on the Habitat Conservation Plan for Santa Clara County.
One or two starthistle plants take over 70 percent of an area when given just two years to proliferate.
“It’s like a cancer infestation,” Weiss said. “You have to get every last cell or it’s going to come back.”
County Parks often cannot use herbicides because of their proximity to water sources and in parts of parks near urban areas controlled burns are out of the question.
Along a bike path in Coyote Creek Parkway, biological controls have lowered the number of yellow starthistles found. Native grasses have returned and starthistle dots the field. In the grasslands, four biological controls have been used to combat the wild weed – including two types of weevils, two types of flies and a rust, or fungus. The USDA conducts extensive tests to determine that biological controls will not have an adverse effect on native plants or animals, Wylde said.
San Benito County has implemented many of the same biocontrols for yellow starthistle.
“In those areas where we have been releasing the weevils it has helped,” Ross said. “It doesn’t give 100 percent control, but over time it will help.”
They are especially tough on what they call “pioneering plants,” Ross said. These are plants that often sprout along roadways, their seeds passed along by car tires.
“We assess it and do control measures,” Ross said. “It’s better to put that work in now in order to protect the environment and range lands.”
Different controls work best based on the life cycle of the plant and creatures protecting them.
“Timing is everything,” Wylde said. “It’s getting the weeds at their most vulnerable life stage.”
Cattle, sheep or goat grazing is an option during winter months when the plants are seedlings. During spring, weevils – especially hairy weevils – feed on buds of the plant.
“80 percent of the seeds can be knocked out by hairy weevils,” Wylde said. “They lay eggs on the flower and feed on the immature flowers.”
Yellow starthistle is not the only weed invading the region. Unsuspecting landowners have purchased many plants that have gotten out of control as ornamentals.
French broom, a native to Mediterranean regions, fills parts of Rancho Canada del Oro and Calero County Park. The green shrubs used to be sold at nurseries. The California Invasive Plant Council lists invasive species and works with nurseries and other plant retailers to keep invasive plants off the market.
French broom, which grows quickly and flowers with bright yellow petals, can grow 6 feet in a few years, but it burns easily and can spread fires.
Derek Neumann, a supervising technician for the Open Space Authority, demonstrated one of the best methods for combating the plant – a weed wrench.
Volunteers often pull out the thicker branches of French Broom and other weeds. They have made a dramatic difference in reducing the coverage of the plant in Rancho Canada from 75-80 percent to 4 percent. But keeping the plant from reseeding is important since each plant can produce up to 8,000 seeds. The seedpods explode when ripe, sending seeds near and far.
“When we first started, we couldn’t even see the creeks,” Neumann said.
San Benito has focused a few of their weed projects on eradication as opposed to control.
“A plant called the artichoke thistle is found in two locations,” Ross said. “It’s almost eradicated in those areas and we’ve been working on it for about four years.”
San Benito weed management partners used herbicides to spray the weeds during spring. Similar methods are being used with purple starthistle, which is common south of Paicines. Precautions are taken near water sources, such as creeks, and hand pulling has been used in those areas.
But even as some weed populations come under control, others are emerging. Barbed goat grass first made an appearance in 2002. Biologists and others involved in weed eradication joke that the plant got its name because not even goats will eat it.
“The foliage is full of silica,” Weiss said. “It’s essentially made of glass.”
So far biological controls haven’t been found to combat the weed, though cooperation among agencies to find methods to control it are underway.
“We need funding for strategic planning and experiments to find out what works,” Weiss said. “We need to plan immediately for invasions.”
Resources
Santa Clara County Weed Management Area
www.sccgov.org/portal/site/ag
San Benito County Weed Management Area
www.sanbenitoweeds.org
California Invasive Plant Council
www.cal-ipc.org
