- Author: Help Desk Team
Bermuda buttercup (Oxalis pes-caprae) has become a tenacious and frustrating weed throughout California. From November through April, bright yellow flowers on leafless stalks and green shamrock-like leaves pop up in many of our landscapes. While it was brought from South Africa as an ornamental plant, it escaped cultivation on its route to being a chronic nuisance. It competes with other plants and is very difficult to control.
Bermuda buttercup develops from underground bulbs that produce a single vertical stem. A loose rosette of leaves will appear at soil level after the first rain. Small, whitish bulblets develop on the stem, and new bulbs form underground. Each plant can produce about a dozen small bulbs each year that easily detach from the plant and will increase the plant's spread quickly.
A couple of our favorite vertebrate pests (gophers and voles) consider oxalis bulbs to be a yummy food source and can spread the bulbs to new locations as they carry them back to their underground dens.
The best way to control Bermuda buttercup is to prevent its introduction into your garden. Don't move soil or plants from an infested site to another location that is free of the weed. Unfortunately, for many of us, it's too late for that tactic. So, what can we do when faced with the cheery yellow flowers popping up throughout the landscape?
Hand pulling can provide control if the entire plant is removed, including the underground rhizome and bulb. It's difficult to find all the bulbs without sifting the soil very carefully. Repeatedly removing the tops of the plants will eventually deplete the bulb's resources, but it can take years to be successful. It's important to remove the tops of the plants before they flower and form new bulbs.
It is difficult to smother Bermuda buttercup with thick mulch or even weed block cloth because it is a strong plant. If cardboard covered with a thick layer of mulch is used to try to smother the weed, continued vigilance in monitoring and pulling new growth will be needed in subsequent years. In one garden, weed cloth was laid under a brick walkway. The following winter, Bermuda buttercup pushed its way up through the weed cloth between the bricks. This made removing the plants even more difficult because the plants were being held in place by the weed cloth.
Several herbicides will effectively kill the tops of the plants, but will not kill the bulbs, so regrowth will occur.
Whatever method you choose to combat a Bermuda buttercup invasion, you will need to be persistent and prepared to continue in subsequent years.
For more information about managing Bermuda buttercup, see this web page: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7444.html
Help Desk of the UC Master Gardeners of Contra Costa County (SEH)
- Author: Kathy Keatley Garvey
Have you ever asked Siri "How cold is it?"
Siri, a computer program known as Apple's "intelligent personal assistant" or "knowledge navigator," is part of Apple's Inc.'s iOS operating system. Folks usually ask Siri for directions. We ask about the weather AND directions.
So on Wednesday noon, Jan. 25, from our Vacaville "weather station," we picked up the Iphone and asked Siri: "How cold is it?'
"It's 53 degrees and I don't find that particularly cold," she said, maybe a little too fiesty. Siri is probably headquartered in Fairbanks, Alaska, where shivering residents experience -70 degrees in January. Or maybe she's based in Grand Forks or Fargo, N.D., where -40 degrees is considered a heat wave.
It's so cold in some of the cities in Alaska, North Dakota and Minnesota--how cold?--so cold that you have to open the refrigerator to heat the house. And, sometimes it's so cold that:
- you step outside and your shadow freezes
- you hear the police telling a robber to "freeze" and he does
- you bake a cake and set it out on the windowsill to cool and seconds later, it's frosted
- you talk to friends and your words freeze, so you have to pick up the letters and thaw them before continuing
- bees are begging to be smoked
So we walked outside to check the newly flowering oxalis for the presence of honey bees. Fifty-three degrees. Scientists tell us that honey bees don't usually fly when it's below 55 degrees, but we've seen bees flying at 50 degrees. So, between 50 and 55, that's a given.
The yellow oxalis seemed to be waiting. Any bees? Yes, one bee. She probably emerged from her hive, shivered a bit, and said to her fellow worker bees: "Let's go, girls!"--or something like that.
So we asked Siri "Do you like bees?"
"This is about you, Kathy, not me," she said.
Still feisty.
Garden Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
(minor correction October 31, 2016)
Client's Request: How can I get rid of oxalis in my yard? I pull it out and think I've got it all, but it just comes back with more gusto the following year. It's annoying, to say the least!
Homeowners and gardeners wishing to eradicate Bermuda buttercup face a tenacious, prolific weed which has devised many successful survival strategies. Each year, after the first seasonal rains, and sometimes before in a dry year, about a dozen ovoid bulbils develop along the length of the threadlike, underground rhizome. These readily detach from the rhizome to replenish the soil seed bank.
Another survival technique of Bermuda buttercup is that, after initial removal by hand, new plants will grow from broken off stem segments left in the soil. Several passes at hand weeding may be necessary to completely remove this new growth. Discouraging survival of Bermuda buttercup can usually be accomplished by gently pulling on the plant and removing all of it just as it is about to flower. By this time, the parent bulb energy reserves are exhausted. The parent bulb should be completely dried out and most young bulbils are too immature to survive disturbance.
Though prevention is the best control method, soil solarization can reduce the bulb population. To be effective, solarization using a clear plastic tarp treated with an ultraviolet light inhibitor must be in place for no less than 4 consecutive weeks during June, July, or August. The sun's rays will heat up the soil to temperatures that are lethal to Bermuda buttercup bulbs (and most everything else in the top several inches). Some researchers investigating approaches for controlling Bermuda buttercup also suggest covering it with stiff cardboard and applying a thick layer of mulch. The goal is to weaken the bulbs and deprive the plant of sunlight, causing an inability to photosynthesize and eventual death by starvation. Chemical control can affect the top growth but is ineffective in preventing bulb germination.
The lack of movement of water and air between compacted clay soil molecules promotes the survival of Bermuda buttercup bulbils. Adding nitrogenrich organic matter will loosen existing soil particles and benefit soil structure by increasing porosity and improving drainage.
While complete eradication is practically impossible to achieve, following strict noncontamination practices, mulching, solarizing, improving soil structure and drainage are all steps gardeners can take to create an environment unfavorable to the establishment and survival of Bermuda buttercup.
For further information on managing this pest, visit www.ipm.ucdavis.edu and download UC's free Pest Notes publication 7444 entitled “Creeping Woodsorrel and Bermuda Buttercup.” (http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7444.html)
UC Master Gardener Program of Contra Costa's Help Desk (CG)
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This is an updated article authored by Chantal Guillemin, UC Master Gardener, and originally published in the March 19, 2011, Contra Costa Times. The HOrT COCO blog editor takes all responsibility for the above updated version.
A minor error was corrected Oct 31, 2016 to reflect, per the Pest Note above that woodsorrel can be a pest in nursery container-grown plants, while Bermuda buttercup isn't. See the Pest Note referenced abov for the specifics..
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Come to the UC MGCC Program's Great Tomato Plant Sale
Walnut Creek 4/2&9, Richmond 4/9, and Antioch 4/16
Click for locations and plant lists!
Dozens of heirloom tomatoes & vegetables chosen especially for Contra Costa
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
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Advice for the Home Gardener from the Contra Costa Master Gardeners' Help Desk
Client's Problem and Questions:
Advice from the CCMGs' Help Desk
"Researchers around the world are investigating approaches for controlling Bermuda buttercup. Some suggest covering infestations with stiff cardboard, then covering the cardboard with a thick layer of organic mulch to kill the plants and weaken the bulbs, making them less capable of competing with desirable plants. Keep the mulch on the infestation until the mulch and cardboard have rotted, then plant competitive ornamentals into the soil-mulch mixture."
The Contra Costa Master Gardener article, "Oxalis: From Ornament to Nuisance" will give you even further insight on controlling Oxalis per-caprae. http://ccmg.ucanr.edu/files/83817.pdf
I know that the management of these weeds is a big challenge and wish you all the best in dealing with it!
Contra Costa Master Gardeners' Help Desk
Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/
- Author: Ben Faber
What a gorgeous fruit. Slice it cross-wise and you have a star-shaped garnish for salad or cooked dish. But you need to find a buyer for it.
The star fruit, or carambola, is a member of the oxalis family. Only one other species is commonly cultivated for its fruit, the less esteemed, more frost sensitive Averrhoa bilimbi. The star fruit is native to Sri Lanka and popular throughout southeast Asia, India, southern China, New Zealand, and Australia. The tree is well adapted to a variety of tropical and subtropical climates and is now cultivated in Mexico, the Caribbean, Central and South America and to a lesser extent, Israel. The main restricting factor in California is frost, the tree being about as cold hardy as limes. The golden-yellow fruit is 3 to 8 inches long and 2 to 4 inches in width with an star shaped cross section. The thin skin, appears waxy but is edible. The sweet to acid flesh is juicy, crisp and mild flavored and usually eaten fresh. It makes an extremely attractive fresh or cooked garnish when cut to reveal its 5 or 6 pointed star cross section. It is also made into relishes and chutneys. The sourer varieties contain more oxalic acid and can be used for polishing brass and removing rust stains. The wood is used for furniture and construction. The fruit is used medicinally as a folk remedy for a large number of maladies including hangover.