Whitetop, also known as hoary cress, is a member of the mustard (Brassicacea) family. It reaches a height of 2 feet and has oblong to lance-shaped leaves. The stems exhibit slight hairiness, while the bluish-green leaves directly attach to the stems without petioles. During spring, densely clustered small white flowers cover the plant (Figure 1). It can sporadically flower on new growth throughout the growing season. The plant produces seeds enclosed in inflated, heart-shaped pods. A mature plant can yield between 1,200 and 4,800 seeds, with seeds remaining viable for 3–4 years.
Whitetop spreads vigorously through an extensive creeping root system, with up to 76% of its biomass located underground. The roots can extend as deep as 12–30 feet. Once established, this invasive species competes with neighboring plants for soil moisture and nutrients. Moreover, it releases allelopathic chemicals that hinder the germination of other species and diminish the vigor of established plants.
Whitetop commonly establishes itself in open, sunny areas, often in areas with recently disturbed soil. It thrives on stored soil moisture from winter and early spring precipitation. It outcompetes other plants and produces seeds rapidly. Capable of growing in salty soil, it is found along roadsides, in new construction areas, areas of the yard without dense plant or mulch cover, and in unhealthy lawns. It grows in most areas from low to high elevations.
Whitetop is perennial and emerges in early spring, with rosettes appearing earlier and flowering in late spring and early summer. If mowed or cut back, it may continue to flower sporadically on new growth. In dry areas, it may go dormant until the following spring. The seeds are dispersed by wind, water, and human activities such as the movement of topsoil, mulches, and animal feeds.
Whitetop causes significant damage to landscapes by spreading through seed dispersion and rapid underground creeping root growth. It outcompetes many ornamental annuals, perennials, and newly planted shrubs if they are too small. Due to its allelopathic nature, do not add removed plants to compost piles but dispose of them in landfills instead. Whitetop is often not easily eradicated due to its rapid growth and tendency to spread into areas where desirable plants are grown.
White top weed, also known as hoary cress, is an invasive plant that can quickly take over yards and gardens. This noxious weed forms dense patches that crowd out native plants and reduce biodiversity. Getting rid of white top weed takes patience and persistence but it can be done. Here’s a comprehensive guide on identifying white top weed and eradicating it for good.
What is White Top Weed?
White top weed (Cardaria draba) is a perennial plant that reproduces both by seed and creeping roots. It is native to Europe and was introduced to North America in the late 1800s as a contaminant in imported alfalfa seed.
Some key facts about white top weed
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Belongs to the mustard family. Has small white flowers that resemble mustard blooms.
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Grows 1-2 feet tall. Forms low, bushy patches.
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Leaves are blue-green in color with white hairy undersides.
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Blooms in spring and early summer. Produces small heart-shaped seed pods.
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Spreads aggressively via lateral roots just under the soil surface.
Why is White Top Weed Problematic?
Once established, white top weed is very difficult to control. A few key reasons it’s considered an invasive weed:
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Fast spreading roots form dense colonies that displace other plants.
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Drought tolerant and thrives in poor, gravely soils.
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Produces thousands of seeds that spread easily by wind and water.
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Unpalatable to livestock once plants bolt and flower.
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Toxic compounds in foliage can taint milk if consumed by cattle.
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Reduces crop yields and forage quality on farms and ranches.
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Very hard to eradicate. Requires persistent management over several years.
How to Identify White Top Weed
Learning to identify white top weed is the first step toward controlling it. Here are the key characteristics to look for:
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Low growing rosettes in early spring before flowering stems emerge.
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Blue-green leaves with whitish-gray hairy undersides.
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Leaves are deeply lobed with toothed edges.
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Small white flowers with four petals bloom in spring.
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Flattened, heart-shaped seed pods form in early summer.
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Fibrous taproot with spreading lateral roots up to 15 feet long.
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Forms large, dense patches that expand outward in circular shapes.
If you spot any plants matching this description, take action promptly to avoid rapid spreading.
Management Options for White Top Weed
Getting rid of white top weed requires attacking it from multiple angles:
Prevention
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Carefully check clothing, gear, and vehicles for seeds after exposure.
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Wash vehicles that have driven through infested areas.
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Don’t move soil or gravel from contaminated sites.
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Plant competitive grasses and forbs to limit invasion.
Mechanical Control
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Manually dig out small patches, removing all roots and stems.
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Mow or weed whip repeatedly to prevent flowering and seed production.
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Use caution when tilling – it can spread root fragments that resprout.
Chemical Control
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Apply systemic herbicides like glyphosate or 2,4-D in early spring and fall.
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Use selective herbicides like chlorsulfuron for spot treating in lawns.
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Multiple herbicide applications are needed over several years.
Biological Control
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Some flea beetles and stem-boring weevils show promise to weaken plants.
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Goats and sheep will graze rosettes but avoid once plants bolt.
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Rotate grazing livestock before plants go to seed.
How to Get Rid of White Top Weed
Here are detailed steps for controlling white top weed based on the size of the infestation:
For Small Patches (Less than 3 feet diameter):
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Manually dig out the entire root system 2-4 inches deep.
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Bag and dispose of all plants parts offsite. Burning is not advised.
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Monitor the area and promptly remove any regrowth.
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Plan on repeating manual removal 2-3 times per season for 2 years.
For Medium Sized Patches (3 – 10 feet diameter):
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Mow or string-trim frequently to 6 inches throughout the growing season.
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Apply systemic herbicide in early spring and again in fall for 2-3 years.
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Reseed treated areas with competitive grasses like thickspike wheatgrass.
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Hand pull or spot spray any remaining plants as needed.
For Large Infestations (Over 10 feet diameter):
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Mow or string-trim before plants bolt and flower to limit seed production.
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Apply high-volume, low concentration herbicide using a targeted method like wiping or spot spraying. Avoid broadcast spraying.
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Revegetate treated areas with an aggressive grass/forb mix to prevent reinvasion.
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Release approved biocontrol agents like flea beetles where possible.
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Plan on control efforts for a minimum of 3-5 years before achieving eradication. Monitor and quickly treat any regrowth.
Prevention Is Key
While certainly labor intensive, getting rid of white top weed is possible with a multi-year management plan targeting the roots. Stopping its initial establishment is much easier than trying to control established infestations. So be vigilant in identifying white top weed early and taking quick action at the first sign of invasion. A small amount of prevention work will save you many headaches down the road!
Suppression and Control Options
Various control options are available for whitetop. The best strategy is to identify and remove newly germinated plants before they flower.
In suitable situations, whitetop can be smothered. Start by cutting plants to ground level in the spring. Remove the debris and cover the area with overlapping cardboard sheets. If needed, you can peg the cardboard down with landscape staples. Next, place 3–4 inches of mulch or wood shavings over the top of the cardboard. Leave this in place for one year.
Solarization using UV-resistant, clear plastic sheeting is another option. With this method, cut the whitetop down to ground level and cover the area with clear plastic sheeting. The soil underneath the plastic is heated, killing the seeds and roots to 6 inches deep over the season. New sprouts are also prevented by succumbing to the heat under the plastic. Remove the plastic once the season is over. Consider lightly incorporating a few inches of compost into the uncovered soil a few inches deep.
Repeated tilling or cultivation of whitetop can reduce the population when exposed roots are removed. If roots are not removed, the weed may spread. Consistent cutting at ground level during the growing season can deplete the stored carbohydrates over several years, eventually killing the plant.
Conventional herbicides provide the fastest, most effective, and most comprehensive control (Table 1). They should be applied in spring before flower buds open, and they are also suitable in early fall.
Of the reduced-risk and organic herbicides we reviewed, none were labeled for controlling whitetop. If you use one of them in an area permitted by the product’s label, only the aboveground portions of the plants will be killed, and they will regenerate from roots. Controlling whitetop in this way requires spraying repeatedly over a few years. Remember, no matter what product you use, you should carefully read and adhere to labels for safety precautions, mixing ratios, and approved application areas.
| Product | Systemic | Conventional | Notes |
|---|---|---|---|
| 2,4-D | X | X | Many formulations are registered for lawn use. |
| Various lawn weed killers | X | X | We found no lawn weed killers specifically registered to control whitetop. However, spraying lawn weed killers containing 2,4-D on the lawn or other areas registered on the label to control other weeds will likely suppress or kill whitetop. Most lawn weed killers have use restrictions at temperatures above 85 °F, where they can form a vapor that drifts, damaging nontarget plants. |
| Glyphosate | X | X | It is very effective when sprayed according to the label. When sprayed correctly, nearly 100% control can be achieved. Avoid getting spray on desirable plants |
| Metsulfuron | X | X | Products containing metsulfuron are the most effective for controlling whitetop. Postemergence herbicides should be applied when plants are in flower to improve effectiveness. Metsulfuron is not readily available to homeowners. Review the label carefully before use. |
- Fire Effects Information System (FEIS). (2023). Cardaria spp. U.S. Forest Service and U.S. Department of Agriculture. https://www.fs.usda.gov/database/feis/plants/forb/carspp3/all.html
- Midwest Invasive Species Information Network. (2023). Whitetop (Cardaria draba). Michigan State University. http://www.misin.msu.edu/facts/detail/?project=misin&id=371&cname=Whitetop
- Monleon, R. G. (1989). Experiences with ammonium glufosinate in Spain. Industrias Chemicas. Conference Proceedings of the 4th ERWS Mediterranean Symposium on weed problems in the Mediterranean climates. Valencia, Spain. Volume 1.
- Qasem, J. R. (2004). Allelopathic Plants 11: Cardaria draba (L.) Desv. Allelopathy Journal, 13(2), 165–172.
- Sterling, G. R. (1951). The control of hoary cress in Alberta. Field Crops Branch Report, Alberta Department of Agriculture.
The authors provided the photos, and Depositphotos supplied the banner .
June 2024 Utah State University Extension Peer-reviewed fact sheet
Taun Beddes, Michael Caron, Jacob Hadfield, and Corey Ransom
Extension Associate Professor | Horticulture | Utah County Director | Juab County
Agriculture and Natural Resources Phone: (385)-268-6535 Email:
Extension Assistant Professor | Horticulture | Utah County
Agriculture and Natural Resources Phone: (385) 268-6530 Email:
Extension Assistant Professor | Agriculture and Natural Resources | Utah and Juab Counties | Juab County Director
Agriculture and Natural Resources Phone: (435) 623-3457 Email:
PSC Dept Phone: (435) 797-2242 Email:
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- Whitetop (Lepidium draba, formerly Cardaria draba) is a persistent, perennial weed that grows in open, sunny areas. It spreads by seeds and rhizomes by several feet in a single season.
- It is common in wildlands, agricultural, and residential areas.
- It rapidly spreads into unhealthy lawns, landscape beds, and vegetable gardens.
- Non-herbicide control involves consistent, manual removal, shallow cultivation, or covering the affected soil with cardboard followed by a 3-inch layer of mulch. Solarizing affected areas is another option.
- Conventional herbicides are effective for suppression and control. We could find no organic herbicides labeled to suppress or control whitetop.
Whitetop, also known as hoary cress, is a member of the mustard (Brassicacea) family. It reaches a height of 2 feet and has oblong to lance-shaped leaves. The stems exhibit slight hairiness, while the bluish-green leaves directly attach to the stems without petioles. During spring, densely clustered small white flowers cover the plant (Figure 1). It can sporadically flower on new growth throughout the growing season. The plant produces seeds enclosed in inflated, heart-shaped pods. A mature plant can yield between 1,200 and 4,800 seeds, with seeds remaining viable for 3–4 years.
Whitetop spreads vigorously through an extensive creeping root system, with up to 76% of its biomass located underground. The roots can extend as deep as 12–30 feet. Once established, this invasive species competes with neighboring plants for soil moisture and nutrients. Moreover, it releases allelopathic chemicals that hinder the germination of other species and diminish the vigor of established plants.
Whitetop commonly establishes itself in open, sunny areas, often in areas with recently disturbed soil. It thrives on stored soil moisture from winter and early spring precipitation. It outcompetes other plants and produces seeds rapidly. Capable of growing in salty soil, it is found along roadsides, in new construction areas, areas of the yard without dense plant or mulch cover, and in unhealthy lawns. It grows in most areas from low to high elevations.
Whitetop is perennial and emerges in early spring, with rosettes appearing earlier and flowering in late spring and early summer. If mowed or cut back, it may continue to flower sporadically on new growth. In dry areas, it may go dormant until the following spring. The seeds are dispersed by wind, water, and human activities such as the movement of topsoil, mulches, and animal feeds.
Whitetop causes significant damage to landscapes by spreading through seed dispersion and rapid underground creeping root growth. It outcompetes many ornamental annuals, perennials, and newly planted shrubs if they are too small. Due to its allelopathic nature, do not add removed plants to compost piles but dispose of them in landfills instead. Whitetop is often not easily eradicated due to its rapid growth and tendency to spread into areas where desirable plants are grown.
How to Control Whitetop Weed
FAQ
How to get rid of white top weeds?
Most lawn weed killers have use restrictions at temperatures above 85 °F, where they can form a vapor that drifts, damaging nontarget plants. Products containing metsulfuron are the most effective for controlling whitetop. Postemergence herbicides should be applied when plants are in flower to improve effectiveness.
How to get rid of white top clover?
- Keep a Well-Fed Lawn.
- Adjust Mowing Height.
- Pull Clover by Hand.
- Use a Weed Killer.
Is white top invasive?
While they may look harmless at first glance, these blooms could be a sign of Whitetop (Lepidium draba)—an aggressive, fast-spreading invasive plant that threatens native landscapes and agricultural productivity.
Can you get rid of white mold on weed?
It can be removed from plants with proper treatment if spotted early on, but any buds with WPM should be discarded as they most likely contain many more spores than your eyes can see.