- Author: Karey Windbiel-Rojas
After all the winter rains you may find yourself dealing with weeds and struggling to control them. The first step in successfully controlling weeds is knowing what weed you have. Well, you're in luck: the UC IPM website contains many useful resources to help you identify and manage weeds in the garden or landscape.
A great place to start is the Weed Gallery, which contains images and identification tips for more than 150 common weeds.
If you think you know the name of your weed, you can use the common or scientific name to view photos to confirm identification. Just use the “List of All Weeds” link from the main weed gallery page.
If you don't know what the weed is, the gallery will help you identify the plant using visual characteristics. First, narrow your search by choosing “identification” in the weed category—broadleaf, grass, sedge, or aquatic plant. That will show you a collection of photos in that category.
Select the photo of the plant form or leaf characteristic that resembles your weed (Figure 1) to see another sub-menu of weeds that exhibit more traits of your weed. Scrolling over a thumbnail image on this sub-menu will bring up several photos of the weed—as a seedling and mature plant, its flower, and seeds—to further help you identify it.
Once you think you've identified the weed, click on the linked weed name, which will take you to a photo gallery page. Here you will find details about the weed's habitat, growth characteristics, and life stages. For many weeds, there is a link to the Pest Notes that will give you information about its management, both chemical and nonchemical. Each page in the gallery also links to the Calflora website to show where the weed grows in California.
The gallery contains other features as well:
- Want to know more about plants and their parts? Illustrated tutorials distinguish among broadleaf, grass, and sedge plants and define plant parts used in characterizing certain plant species.
- Need to find out what weeds are in your lawns? The broadleaf and grass categories link to an identification key for common turf weeds.
- Didn't find your weed? See the weed identification tool under “More information” to search the UC Weed Research & Information Center (WRIC) technical weed key.
You can find the weed gallery page on the left-hand column of the main Home & Landscape page on the UC IPM web site or from the many weed-related pages. To access the weed gallery directly, visit https://ipm.ucanr.edu/PMG/weeds_intro.html.
Visit UC IPM's Weeds library page to find general weed management tips, individual weed-related Pest Notes, the weed gallery, key to weeds in turf, and other useful resources. https://ipm.ucanr.edu/PMG/menu.weeds.html
[Originally featured in the Spring 2024 edition of the Home & Garden Pest Newsletter]
- Author: Jeannette Warnert
Weeds present a serious economic problem for farmers, a major headache for vegetable gardeners, and an unattractive appearance in landscapes, but herbicides are not the only solution.
“Studies have shown that more than 70 percent of weeds in lawns and ornamental plantings can be controlled based on good cultural practices,” said Dr. Clebson G. Gonçalves, a horticulture expert and farm advisor with UC Cooperative Extension in Lake and Mendocino counties. He spoke about springtime weed identification and management during a recent urban horticulture webinar offered by the UC Integrated Pest Management Program. “To control weeds, start with good soil; choose suitable plants; and mow, prune, water, and control pests to ensure dense and healthy turf and ornamentals.”
There are several definitions for the term “weeds,” but generally speaking, it can be defined as a plant out of place. Gonçalves used common bermudagrass as an example.
“Bermudagrass is one of the most desirable grass species for golf courses, sports fields, and residential lawns. But out of place, it's extremely difficult to control. It's adaptable to a wide range of environments and can reproduce by rhizome, stolon, and seeds,” he said.
When deciding how to control weeds in lawns and landscapes, Gonçalves suggests gardeners start by identifying the species. The Weed Research and Information Center at the University of California, Davis, offers a free online weed identification tool. Users input characteristics of the weeds – such as weed type (grasslike, broadleaf, woody), where the weed was found, leaf characteristics, stem characteristics, floral characteristics, life cycle, growth habit, etc. – and the tool offers potential species. The UC IPM Program maintains a weed photo gallery of species commonly found in California.
Knowing the species helps determine best practices for control. For example, nutsedge is a grass-like weed that develops nut-like tubers on the roots. The tubers are key to nutsedge survival. Dig deeply into the soil to remove the tubers on mature nutsedge roots. To limit tuber production, remove small nutsedge plants before they have 5 to 6 leaves.
Gonçalves suggests following the principles of integrated pest management to control the weeds by first considering practices that are effective and environmentally sound.
Preventative
- Avoid bringing weeds into your garden and landscape in the first place. Gonçalves suggests using weed-free soil and compost. “It's better to spend a little more money up front when you buy topsoil and compost, than spending even more money later for weed control,” he said.
- Inspect plants at nurseries before bringing them home to see if there are any weeds in or under the pot.
- Clean the mower between lawns. “This is especially important for landscaping companies that work in different locations on the same day. It is important to clean all the equipment before starting in a different location.,” Gonçalves said.
- Never let weeds go to seed. “A lot of species – such as dandelions, bermudagrass, and annual bluegrass – can produce a new seed head very quickly,” Gonçalves said. “If you mow every other week, that's enough time for these weeds to produce new seed heads and disperse seeds. It's better to mow once a week or even more often to prevent the production of seed.”
Cultural
- Soil aeration. “It's very important to alleviate soil compaction in established turf. You will have better water infiltration, greater nutrient availability and more oxygen underground, which promotes plant health and growth above and below the ground,” Gonçalves said.
- Don't leave soil exposed. Limit the area for weeds to grow by utilizing dense plantings. “When you have light and moisture, you have weeds coming up,” he said.
- Mow uniformly at a height of three inches or more. The tall and dense turfgrass canopy will shade the ground and prevent the germination of several weed species.
- Fertilize uniformly.
Mechanical
- Pulling weeds. “Every weed can be controlled by hand. If you have the time to pull by hand, that is recommended. There is some pleasure in pulling weeds. It can be used as therapy,” Gonçalves said.
- Mulches. Wood chips, stone, leaves or compost – especially on top of landscape fabric – can control weeds.
- Flaming. Very effective, primarily in the early stages when weeds are small in stature. But if they are aggressive weeds with strong taproots, such as dandelions and buckhorn plantain, they can grow back very quickly.
Herbicides
- Organic. Always use certified products. “Don't make homemade herbicides. They are still pesticides and can be dangerous,” Gonçalves said. Corn gluten meal is the only organic pre-emergent herbicide. Organic herbicides are available for consumers in different combinations and concentrations. “Vinegar-based herbicides can be very expensive, but other options such as citric acid-based, caprylic acid-based, clove-oil-based, or ammonium nonanoate-based can be more affordable and provide vinegar-like weed control,” Gonçalves said.
- Synthetic. “Many synthetic herbicides also are available for consumers. But the question is: Do you need it? Keep in mind that, all options presented above must be considered first before deciding to use herbicides,” Gonçalves said.
- In both cases, synthetic and organic herbicides are pesticides. Carefully read and follow the label directions.
Learn more:
- 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)
For many of us, gardening involves a constant battle with weeds. Basically, a weed is nothing more than a plant growing where it is not wanted, the classic example being dandelions in the lawn. But as the old saying goes, “One man's trash is another man's treasure,” and there are many “weeds” that are, in fact, completely edible. Good examples are purslane (portulaca oleracea), miner's lettuce (claytonia perfoliate) and, yes, even the unwanted dandelion; many tasty recipes for them can be found in a simple internet search. Looked at another way, a weed may simply be an unloved flower.
According to the Farmer's Almanac, weeds fall into three distinct categories: weeds, noxious weeds, and invasive weeds. A (basic) weed is simply a plant that causes health problems for either humans or animals (as in allergy seasons when certain grasses, seeds, or pollens are released) or causes economic losses or ecological damage, or is simply undesirable where it grows (crabgrass is a classic example). A noxious weed is any plant designated by federal, state, or local government as one which can cause injury to agriculture, wildlife, public health, recreation, or property. Noxious weeds vary from state to state and county to county (field bindweed is noxious in California). An invasive weed is a non-native that competes with natives and may crowd them out and alter ecosystems (English ivy, for example, which has also become invasive in Bidwell Park).
There are precautions to take that will help prevent the spread of unwanted seeds. It is important to make sure gardening tools and pots are cleaned after each use, a step that many people overlook. Immediately clean tools that have been used to remove dead or diseased leaves. If and when purchasing soil and amendments at a garden center, be sure to buy quality materials that are comprised of manure, compost, or “garden” soil that are preferably weed free. Although more expensive, selecting an amendment known to be weed free is worth the investment.
Once your plants are getting established, try to water them by hand or through a drip system. Limiting water applications to areas around your plants' roots will discourage any stray seeds from germinating nearby. Avoid over-fertilizing: over-fertilization encourages more vigorous competition with your plants from any weeds that may be present.
It may take several seasons, but by being diligent weeds can be controlled. It is especially important to remove them before they flower and produce seed. UC weed scientists counsel that “one year's seed results in seven years of weeds.”
It is also helpful to remember that in nature, weeds play an important role. They can resist conditions like drought, acidic soil, lack of humus, and mineral deficiencies. Weeds protect topsoil from eroding away in heavy rains and strong wind. They provide cover and shade for soil microbes and insects. And weeds can reveal important information about the health and pH of our soils -- for example, certain weed species are confined to acidic soils and others to alkaline. The presence of some weeds, like Curly Dock, let you know that soil in the area is frequently wet and saturated. So don't dismiss the weeds in your yard out of hand – they may have something useful to tell you!
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at 530-552-5812. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
- Author: Ben Faber
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