Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Response from the MGCC's Help Desk: Thank you for contacting the UC Master Gardener Program Help Desk with your request for weed identification. We really appreciate the picture that you sent along too. It was very helpful.
From your picture, this appears to be a weedy mallow. There are two types of weedy mallow that are common in California, the common mallow (Malva neglecta) and little mallow (Malva parviflora). Both of these mallows are also known as cheeseweed.
Malva (mallow) species look very similar. Neglecta and parviflora can only be distinguished by comparing the flower petals and fruit shape. Flowers bloom nearly year-round. They are small, white to pale pink and about 2/5 of an inch in diameter. Flower clusters are found at the bases of leaf stalks. Neglecta petals are longer than parviflora petals and the fruit of neglecta are smooth while those of parviflora are wrinkled. The fruit for both is sometimes described as looking like a tiny wheel of cheese with wedge-shaped sections therefore giving them the common name of cheeseweed. Each wedge of the fruit contains one reddish brown kidney shaped seed.
These annuals begin growing from seed with the first rains in the fall and quickly develop a deep taproot that becomes woody and makes the plant difficult to remove by hand or even with tools (as you have found). Left alone, these plants will spread and can grow between 2 to 5 ft. tall.
- Mallows are best controlled mechanically by hoeing or pulling out young plants.
- Young mallow can also be killed by cutting them off at the crown but older plants may re-sprout from the crown.
- Solarization is not effective for mallow control nor is flaming.
- Insects do feed on mallows but there are none that are specialized for control of these weeds.
- There are no chemical controls available for home use that are effective for controlling mallows. Mallow is one of the few weeds that glyphosate (“RoundUp”) is ineffective in controlling.
- Cultural control can be done by planting competitive desirable plants in areas where mallow is a problem. The shade provided by these plants will reduce germination and growth of mallow seedlings.
- Mulches can also be effective. At least 3 inches of organic mulch, such as bark or wood chips, will make it difficult for the seedling to emerge and will screen out the amount of light that mallow requires to effectively sprout. It is important to maintain the needed depth otherwise, the seedlings can push through and become established again.
I'm including two links that have additional information:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74127.html
http://ipm.ucanr.edu/PMG/WEEDS/little_mallow.html
I hope this information is helpful to you. Please let us know if you have any questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (JMA)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, 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 (//ucanr.edu/blogs/CCMGBlog/)
Most weeds are classified as annuals, biennials, or perennials. Annuals complete their life cycle (germinate from seed, grow, flower, set seed, and die) in one year or less, biennials generally complete their life cycle in 2 years, and perennials live longer than 2 years.
Examples of winter annual weeds include chickweed, little mallow, and annual bluegrass. They germinate and actively grow during fall and winter, then produce seed and die by the hot summer months.
If allowed to set seed, annual winter weeds can continue to grow and spread every year. Many of these weeds can produce hundreds of seeds from a single plant that may germinate the following year if conditions are right.
Learn about control options in the UC IPM Pest Notes publications, Weed Management in Landscapes and Weed Management in Lawns.
- Author: Kathy Keatley Garvey
We've seen monarchs, Gulf Fritillaries, Western tiger swallowtails, buckeyes, and fiery skippers nectaring on our Mexican sunflowers. But nary a common checkered skipper.
Where, we wondered, are the common checkered skippers?
Just as we were thinking that the common checkered skipper (Pyrgus communis) is not all that common and is not living up to its name, it appeared. Right on cue.
It nectared on the Tithonia and then fluttered away.
It will be back, according to butterfly guru Art Shapiro, distinguished professor of evolution and ecology at UC Davis, and Bohart Museum of Entomology associate Greg Kareofelas.
Why?
Its host plant is mallow and last spring we planted several tree mallows, Lavatera maritima--those drop-dead gorgeous plants with purple-throated pale lavender flowers. A bonus: unlike we Californians, the mallow loves the drought. It does not get thirsty. Plus, it attracts a variety of insects, and blooms much of the year.
Shapiro, who has monitored the Central California population of butterflies for more than four decades and maintains a website, Art's Butterfly World, says this about Pyrgus communis on his educational website:
"This familiar insect appears to be found from sea level to tree line-but things are more complicated than that. At the molecular-genetic level, the populations along our transect are apparently two different species. One is multiple-brooded and occurs as high as Lang Crossing (5000') on the Sierran West slope, and then again in Sierra Valley at 5000' on the East slope. These populations today breed largely on introduced weeds of the genus Malva (in the Sacramento Valley also on the native Alkali Mallow, Malvella leprosa, and on the now rare Checkerblooms, genus Sidalcea, in tule marshes). The other is single-brooded, occurs above 6000' (including Donner and Castle Peak) and breeds only on native Sidalcea. There are very slight 'statistical' differences in pattern, but the genitalia are the same. There seem to be occasional strays of the lowland animal picked up at Donner, mainly late in the season. In southern California occurs a morphospecies, P. albescens, which differs from communis in genitalia and is, like it, multiple-brooded. This animal, however, is molecularly indistinguishable from the univoltine Sierran (genitalic) communis!
"The lowland animal occurs anywhere in the open where hosts are nearby, including urban vacant lots and around ranch buildings and corrals. The montane animal occurs in open coniferous forest with Sidalcea in the understory, and along wood roads and paths. Both visit a great variety of flowers avidly. The flight seasons are March-November in the Central Valley, June-August in montane sites, and late March/April-October at Sierra Valley. (At Sierra Valley the univoltine animal is as close as the top of Yuba Pass.)
"Males are perchers, generally well off the ground, and extremely energetic fliers. They often appear blue in flight (females, lacking the silky hairs, do not)."
Plant mallow and they will come!
/span>Advice from the Help Desk of the
Master Gardeners of Contra Costa County
Client's Request: I've been noticing this “weed” growing in my garden lately. At least, I think it's a weed although the leaves seem to resemble some garden geraniums. Is it a weed, and if it is, what do you suggest I do to get rid of it? Some JPG photos I took of the “weed” are below. ... and (editor's addendum) can you eat it?
MGCC Help Desk Response: Thank you for the photographs. The plant is a type of Mallow, probably “Little Mallow” (Malva parviflora), often also commonly called Cheeseweed for the "small wheels" of cheese like fruit it produces. And yes as the common name implies, it is a winter-sprouting annual weed or sometimes a biannual weed. It quickly develops a deep taproot, making it difficult to eradicate. Pulling them up or hoeing them off as soon as you notice them is the best way to control their spread.
Cheeseweed can also be toxic to cattle and can reduce egg quality if fed to laying hens.
Additional information on this weed and its control can be found at the University of California's website http://www.ipm.ucdavis.edu/PMG/WEEDS/little_mallow.html and http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74127.html.
As above, early-on mechanical (hoeing) and cultural control (weeding) are about the only effective controls for home gardeners. Control by herbicides has not proven effective. In fact, this mallow is one of the few weeds not controlled by glyphosate (i.e., RoundUp™).
I hope that this information is helpful. Good luck on controlling it. I've had them in my garden off and on for years and can't seem to keep them out although I find that if caught early enough they aren't hard to keep them at bay and aren't that much of a pest.
HOrT COCO Blog Editor Addendum: It's been brought to my attention that Cheeseweed is edible... and by quite a few cultures... but not by this gardener/editor... see the various comments on its use as greens, etc. by Googling "is cheeseweed edible?". You are on your own for that adventure though...
Help Desk of the Master Gardeners of Contra Costa County (JL)
Note: The UC Master Gardeners 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/blogcore/blogroll.cfm).
- Author: Oleg Daugovish
Using organic herbicides in production fields and non-crop areas.
The forecasts call for rainy winter and that means a lot of weeds. During dry times perennial weeds tend to grow better than annual weeds, since perennial structures such as underground rhizomes or tubers can support them and give competitive advantage. Seed of annual weeds in dry soil may have been losing viability, senescing or eaten during this time, but many have remained dormant and look forward to the wet winter us much as the rest of us.
Controlling weeds ‘organically' is always an extra challenge whether you are in a certified field or in an area where synthetic herbicides are not desired. Hand-weeding, already expensive, is even a greater burden with limited labor availability, and frankly not much fun either. Of course sanitation and prevention, mechanical and cultural management are essential in organic systems. That requires time and commitment and can quickly become your not-so-favorite pastime.
Organic herbicides have traditionally been contact materials with no systemic activity. This means that they only affect tissue that they contact and do not translocate through the plant like most synthetic herbicides. Thus, good coverage is critical for these contact materials. Many years ago the first herbicides were sulfuric acid and diesel fuel, current organic materials are often acids or oils too, although a lot more benign.
Recent trials by the University of California weed scientists showed that several organic herbicides provided decent control of easy to control pigweed and nightshade when they were small. When weeds were 12 days old, a mixture of 45% clove and 45% cinnamon oil, 20%-acetic acid and d-limonene gave 61-89% control; however only d-limonene controlled 19-day old weeds and none was effective on one-month old ones. As weeds get bigger they also develop a protective cuticle that minimizes efficacy of these herbicides.
This year we conducted trials with a recently OMRI approved herbicide for row crops, trees and vines that is a mix of caprylic and capric acids. It disrupts cell membranes of plans and causes the contents to leak and plants to desiccate. It worked well at 6 to 9% by volume mixture with water and gave 90% control of little mallow and >95% of annual sowthistle compared to untreated checks. We have also tested it in organic strawberry furrows before planting the crop to prevent potential injury from drift. Furrow cultivation does not get close to the plastic mulch that covers the beds to prevent tears, so the weeds in that zone are good target for the herbicide. This fatty acid herbicide provided excellent control of common lambsquarter, reduced the growth of common purslane but didn't do much for yellow nutsedge - one of our notoriously difficult to control perennial weeds (Figure). The bigger weeds need higher rates (9% is the maximum labeled rate) and better coverage. When you have multiple layers of weed leaf canopy and diverse architecture some plants or their parts may be protected by others that intercept the deposition of the herbicide. When on target, this contact material acts fast – you can see results within 2-3 days, however, it does nothing to weed propagules in soil and has no residual activity against wind-dispersed weed seed that fly in after application. This means the control does not last and you will need additional applications or other control measures. Repeated application is not a problem in a non-crop area and is a great way to deplete your weed seedbank, but crop protection from drift, such as shielded sprayers, is necessary to avoid off target plant injury.
Figure. Weed control in strawberry furrows prior to planting with 9% by volume of fatty acid herbicide (top) and weeds in untreated check (bottom)