Dyer’s Woad

Isatis tinctoria

Class A Noxious Weed

This plant is new to the state and has been designated a Class A Noxious Weed by the New Mexico Department of Agriculture.

Agricultural Threat

This plant threatens our state's food security and economy by reducing agriculture yields and/or degrading soil resources.
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Wildlife & Ecosystems

This plant is detrimental to native ecosystems, negatively impacting the quality of forage for wildlife and reducing biodiversity in plant communities.
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QUICK FACTS

Valued as a crop and tolerated as a useful weed from Europe to the Eastern U.S., dyer’s woad is woefully suited to become ecologically invasive in New Mexico. Highly adaptable, it has no issue growing in harsh conditions such as clay-heavy, alkaline, and rocky soils, which are so common in our arid landscape.
Under these conditions, it thrives openly without cultivation (especially in neglected or open areas), out-competing native or other desired plants easily, often forming large monocultures that spread quickly and exhaust soil resources. The result is vast ecological and economic damage, as these monocultures not only reduce the available forage for wildlife but also may leach toxic compounds into the soil.
This plant has quite the arsenal of competitive strategies: it produces a massive amount of easily dispersed seeds, which have the ability to germinate in the fall or winter and generate a robust taproot in addition to its sprawling lateral roots.

1. Overview

family	Brassicaceae – Mustards	origin	Southeast Russia
life cycle	Biennial or Annual	other names	Marlahan mustard, Asp-of-Jerusalem, Glastum, Devil’s weed

Dyer’s woad: the unassuming plant that once turned medieval wardrobes blue, adorned the tombs of Egypt, made warriors fearful, and eventually turned traitor in the American Southwest.

Valued as a dye crop by ancient empires, dyer’s woad persisted through the centuries until it was purposefully brought to the United States. The plant quickly spread west, where it displaced native plant communities and took over rangelands. Unlike other similar weeds, dyer’s woad thrives on neglect; It is happy to move into overlooked areas that haven’t even been disturbed. If not caught early, it will quickly take over a field and render pastures economically useless.

History of Dyer's Woad

If you needed the color blue before the 17th century, dyer’s woad was your primary option. Cultivated as a dye crop for millennia, the blue-green leaves would produce a dark blue pigment called indigo after a fermentation process. As an annual or biennial, it was a reasonably unintrusive plant farmed across Europe and Eurasia without consequence. Eventually, it was brought to the Eastern United States by settlers who still valued it as a fabric dye, where it is still grown today as a natural blue pigment. In the Eastern states, dyer’s woad is still considered a safe crop that is easily contained. In the West, however, the plant quickly showed that under the right conditions, its true potential for invasion would be unleashed. [1,2]

In the medieval era, wine was the most internationally traded item, followed closely in second place by dyer’s woad. This plant, among others, produced the pigment indigo, which, alongside imperial purple, were the two most important dyes in history. Dating back to the Roman and Egyptian dynasties, dyer’s woad was used for writing, painting, and cosmetics. The Celts used the blue pigment as a body paint in battle. [2]

From the 15th to early 19th centuries, the woad industry boomed in Europe, though it had better success in the dry climates of France and Italy (British woad was considered mildewy and inferior). It found its way to the colonies as an alfalfa seed contaminant, where dyers were happy to let it stay. The English Mennonites took a particular interest in woad for dying their homespun fabrics. During the colonial period, the Mennonites were quite happy with the dryer climate of the New World and wildly cultivated the plant. To this day, dyer’s woad is propagated in the Eastern United States as a “natural dye,” though it quickly dies off without human intervention due to the East’s harsh climate. [1,2,4]

Then, it migrated west. As settlers moved west, they inevitably brought with them the seeds of the east. No one foresaw dyer’s woad’s genetic predisposition to arid, alkaline soils. As soon as the plant touched western soils, it no longer needed cultivation. It quickly invaded forests and rangelands, where it persisted season after season, eventually becoming the noxious weed we know today. It is listed as introduced in fifteen states and four Canadian provinces. [1,5]

2. ID Guide

What does it look like?

Dyer’s woad grows as a winter annual, short-lived perennial, or biennial, which appears blue-green with stems topped with large umbels (shaped like an upside-down umbrella) of small, bright-yellow flowers (see Gallery below. Typical of mustards, dyer’s woad has four petals in a cross shape. Look out for reddish stems often seen at the plant’s midsection – this is a distinguishing feature of dyer’s woad. [1,3,4]

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Key Features

Plant: Young plants germinate as a rosette; at this stage, the basal leaves may have some hairs known as trichomes. Multiple stems arising from a central stalk; almost 20 from its basal (first germination) stage, but usually seven at maturity. The stems mature to a length of about 1–5 ft. Although in higher elevations, 6,300 feet and above, the plant may be on the shorter side, averaging 1-2 feet. The plant branches into an umbrella shape at the top. [1,4]

Leaves: Oval to lance-shaped and blue-green, arranged alternately on the stem, with irregularly toothed margins. The adult leaves clasp the stem and have a white to cream-colored midvein from the base of the leaf to the tip. The leaves at the base of the stem are usually largest at the base (1-4 inches long) and get smaller as you go up the stem. [1,4,6]
Flowers are small and yellow, each with four petals arranged in a cross shape, and sepals that are just over ⅛ inch long. The inflorescences cluster, forming compound raceme panicles (umbrella shapes) at the top of the stems (See Gallery below). [1,4]
Seeds: Flat, teardrop-shaped, and suspended from the stems from which the flowers used to grow. The seed pods begin green and, when they finish maturing, are dark purplish-brown to black. [1,4]
Roots: The plant has a thick taproot that can be fleshy or woody. This taproot can grow up to five feet in depth, giving the plant an advantage in rocky or sandy soils. Its lateral roots grow primarily in the top 12 inches of soil. [1,4,6]

kschuster, inaturalist.org

The flowers cluster, forming compound raceme panicles (umbrella shapes) at the top of the stems.

Anton Gjeldum, inaturalist.org

Young plants germinate as a rosette; at this stage, the basal leaves may have some hairs known as trichomes.

Cesar Garcia, inaturalist.org

Fruits ripen in June and July and fall to the ground in one piece, usually facilitated by wind or rain.

carlo_catoni, inaturalist.org

Leaves are oval to lance-shaped and blue-green, arranged alternately on the stem, with irregularly toothed margins.

jucasony, inaturalist.org

The mature stems grow to about 1–5 ft in length. At higher elevations of 6,300 ft and above, the plant may be on the shorter side, 1-2ft on average.

Jordi López-Pujol, inaturalist.org

The seed pods begin green and, when they finish maturing, are dark purplish-brown to black.

3. Infestation Basics

“In England, it is often found in old lime pits and chalk quarries—thus indicating an alkaline soil requirement. It thrives in rich soil and soon exhausts it to such an extent that in former times, the woad crop had to be frequently shifted to new land.” [7]

-Lawrence J. King, 1957

Impacts

Where does it grow, and how does it spread?

Dyer’s woad is adept at outcompeting plant communities throughout the West and establishes monocultures in pastures, woodlands, roadsides, or anywhere, really, where the seeds have been dispersed.

This weed relies entirely on seeds to reproduce. The seeds themselves develop inside of seedpods, which generally land and germinate around the parent plant but are easily dispersed to new locations by wind and waterways. Humans also play their part by transporting the seeds on their clothing and machinery or, in some cases, by intentionally introducing them as a ‘desirable crop.’

During its first season, dyer’s woad develops roots and sprouts, reaching its initial stage as a rosette of basal leaves. The plant will bolt the following season, and flowers and seeds soon follow. However, a small portion of these plants can actually flower during the first growing season. Seedlings that germinate in the fall will overwinter as small rosettes and develop a sufficient root system to support them all the way to the flowering stage the following season. [1,4]

Flowers typically bloom from April to July. Fruits ripen in June and July and fall to the ground in one piece, usually facilitated by wind or rain. Seeds typically do not spread far from the plant but may be carried by mechanical means or waterways. The dry umbrella-shaped flowerheads easily hook into machinery, allowing for further dispersal. [1,4]

Dyer’s woad is predisposed to survive in arid environments with alkaline soils. These climates, such as those found in the southwest, allow for less competition from more desirable plants, and thus enable dyer’s woad to exploit these harsh soils and form quick monocultures. The plant is somewhat shade-tolerant, but prefers open, sunny areas. Dyer’s woad has a strong preference for alkaline soils, and it easily dominates even in difficult rocky soils. Not only that, when it gains a foothold in rich, fertile ground, dyer’s woad will quickly overtake and exhaust the area’s nutrients, possibly even resulting in its own demise. [1,4,6]

Key takeaway: Dyer’s woad is adept at exploiting and exhausting soil resources in the West. Its monocultures can spread incredibly quickly, and the seeds are easily dispersed by wind, water, and people.

Why is it so invasive?

Dyer’s woad poses a threat to plant communities across the southwest due to a cocktail of powerful traits: allelopathic seeds, the ability to germinate in both fall and spring, and a deep taproot with which to establish nutrient reserves.

Dyer’s woad opportunistic reproductive strategy is put into overdrive in the southwest’s delicate arid environment. For one, its seed pods contain chemical germination inhibitors, delaying sprouting until the substances are fully leached away. While many seeds rot before this process is complete, this trade-off ultimately favors a takeover by dyer’s woad—it suppresses its competitors, ensuring that when the woad’s seeds do germinate, they face little resistance.

Its early emergence and deep taproot allow this plant to hoard resources; in a relatively short time, dyer’s woad is able to deplete soil moisture before other species even have a chance to emerge. This strategy exploits our environment’s pre-existing characteristics—low water availability, dry alkaline soils—turning a natural limitation into an opportunity for aggressive expansion.

Once established, dyer’s woad doesn’t just survive; it reshapes its surroundings and quickly establishes large, abundant monocultures. Germinating in fall or early spring—while native species remain dormant—it builds a nutrient reserve before its competitors even break the soil surface. By the time warm weather arrives, it is already outpacing and displacing neighboring plants before they can take hold. [1,4]

Key takeaway: Even healthy, well-established plant communities are vulnerable to an infestation. Dyer’s woad is not confined to neglected roadsides or disturbed areas—it exploits diverse climatic conditions, allowing it to invade rangelands, croplands, and native habitats alike. Its self-reinforcing strategy of resource dominance and chemical suppression ensures its continued spread.

Common risk factors for invasion

Poor land management: Dyer’s woad is not confined to areas of neglect, and can become established even in managed landscapes; practices such as overgrazing, lack of crop rotation, and inadequate weed control increase vulnerability to invasion.
Site dryness: Dyer’s woad spreads much more easily on drought-prone, rocky, or sandy sites. These areas are challenging conditions for most plants, and thus, there is often little to no competition that can challenge dyer’s woad. Monocultures spring up very quickly as a result.
Alkaline soils: Common across the southwest, these soils are composed of clay and have a pH greater than 8.5. With poor soil structure and below-average ability to absorb water, these soil conditions can be harsh. Perhaps again due to a lack of competition, dyer’s woad is highly successful in these circumstances.
Open spaces: Open sites with long days of full sunlight and little canopy, such as roadsides, pastures, fields, meadows, and sparse woodlands, are at risk for particularly aggressive infestations.

Ecosystems & Wildlife

As the basis of food chains, plants provide the backbone to the rest of the ecosystem. From pollinating insects and migrating birds to our distinctive wildlife, they have all evolved to rely on the plants native to the land, and thus rely on those communities for their complete nutrient supply. Dyer’s woad displaces native plants from their ancestral landscapes, resulting in a loss of species biodiversity that has branching effects throughout the ecosystem, including reduced forage availability for game and other wildlife. [4]

Agriculture & Economy

Working landscapes such as farms and pastures are heavily affected by dyer’s woad infestations across the West. Dyer’s woad is known to reduce available forage for domestic livestock, leading to decreased agricultural economic health. In 1981, the presence of dyer’s woad cost Utah ranches an estimated $2 million collectively. Rangelands suffer more greatly than active croplands, as the frequent disturbance and accessibility of food crops provide less-than-ideal conditions for the plant. While a chemical composition has not been established, the plant is believed to have allelopathic properties, not from the roots but from decomposing seed pods that fall to the ground near the parent plant and poison the soil. This adds to the difficulty of managing infestations by overwhelming dyer’s woad with more desirable plant communities. [1,4, 6]

4. Management Strategies

Because this plant can quickly displace existing vegetation, identifying the plant early is key. Once established, dyer’s woad relies primarily on the chemical properties and sheer abundance of its seeds to assert dominance over the landscape. Management thus focuses on preventing seed formation and germination. Removing the crowns before seeds become viable is essential to the plant’s eradication. Early detection and removal of plants before flowering can also significantly reduce seed production. [1]

Mechanical methods, such as hand-pulling or digging, can be effective as long as the taproot is fully removed to prevent regrowth. Mowing can limit seed production in the short term, but may be counterproductive. Although mowing can limit seed production in the short term, plants may respond by producing seeds later in the season, thereby limiting the effectiveness of this strategy on its own. [1] Combining methods can greatly increase your chance of success with this plant.

Control is much more manageable in domestic croplands compared to rangelands and forests, where access to all areas is often hindered by rough terrain. All livestock find the plant unpalatable. Additionally, some evidence suggests that grazing may do more harm than good; a study found that sheep likely did more damage to the few remaining grasses than the invading species. [1]

DO’s

Uproot plants early in their lifecycle, ideally before they flower. This prevents seeds from forming and spreading. Ensure the entire taproot is removed to prevent regrowth.
Clean equipment, vehicles, and tools after working in infested areas. Seeds can cling to machinery and travel to new sites.
Frequently check fields, rangelands, and open areas for early signs of infestation. Early detection is crucial for effective management and minimizing the spread.

DON’Ts

Let the plant flower and set seeds, as a single plant can produce thousands of seeds. Immediate action is essential to control spread.
Ignore infestations in remote areas. Even in inaccessible or less-visited regions, unmanaged infestations can rapidly spread.
Underestimate Its resilience. Dyer’s woad can survive in harsh conditions with poor soil. Assuming it won’t thrive in a specific area can lead to unchecked growth and invasion

** The following information is provided courtesy of the UC Weed Research and Information Center. The Taos Soil and Water Conservation District does not endorse the use of any particular product, brand, or application thereof. **

Dyer’s woad can be suppressed non-chemically by repeatedly removing or tilling rosettes before they bolt. Hand-pulling, mowing, or targeted grazing helps exhaust root reserves and prevent seed set.

Hand-pulling	Hand pulling may be very effective provided the crown is removed. Hand pulling is easiest after the plants have bolted but should be done before seed set. It is important to visit the site 2 to 3 weeks later to rogue plants that have resprouted or were missed the first time through. It is necessary to follow up for several years to prevent reinfestation.
Mowing	Mowing is not effective due to resprouting from the crown, but mowing multiple times can reduce root reserves and seed production. Dyer’s woad populations can be reduced if seed production can be prevented for a few years by cutting off the seed stalks and removing them from the field. Close clipping (2 inches from the soil surface) is more effective. This should be done as soon as possible after flowering to minimize resprouting and prevent seed production. Multiple visits to the field may be necessary to minimize seed production on resprouting plants.
Cultivation	Spring cultivation can control infestations in crop fields but is not practical in most range settings.

Livestock generally avoid eating dyer’s woad. However, significant reductions in dyer’s woad have been observed when livestock are forced under heavy grazing pressure to consume dyer’s woad. The plant is more palatable before bolting and grazing should be done before flowering to minimize seed production.

The effect of fire on dyer’s woad is not well known, but it is likely that even if fire kills the above-ground part of the plant, it will regenerate from root buds on the crown

Insects for biological control of Dyer’s woad are not available in the U.S. but are being evaluated. A native rust fungus (Puccinia thlaspeos) causes systemic infection in dyer’s woad. Infected plants may appear chlorotic, stunted, malformed and have reduced seed production. Even though the disease is systemic, plants derived from the seed of infected plants did not show symptoms of infection. The effectiveness of this fungus is not known at this time.

The following specific use information is based on published papers and reports by researchers and land managers. Other trade names may be available, and other compounds also are labeled for this weed. Directions for use may vary between brands; see label before use. Herbicides are listed by mode of action and then alphabetically. The order of herbicide listing is not reflective of the order of efficacy or preference.

2,4-D

Several names

Rate: Broadcast treatment: 2 to 3 qt/acre (1.9 to 2.85 lb a.e./acre). Spot treatment: 1% v/v solution

Timing: Postemergence from seedling to rosette stages.

Remarks: 2,4-D is broadleaf-selective and has no soil activity. It may require repeat application. It is an effective treatment for seedlings that may emerge following mechanical treatments. Do not apply ester formulations when outside temperatures exceed 80°F.

Aminocyclopyrachlor + chlorsulfuron

Perspective

Rate: 4.75 oz product (Perspective)/acre

Timing: Postemergence and preemergence. Postemergence applications are most effective when applied to plants from the seedling to the mid-rosette stage.

Remarks: Perspective provides broad-spectrum control of many broadleaf species. Although generally safe to grasses, it may suppress or injure certain annual and perennial grass species. Do not treat in the root zone of desirable trees and shrubs. Do not apply more than 11 oz product/acre per year. At this high rate, cool-season grasses will be damaged, including bluebunch wheatgrass. Not yet labeled for grazing lands. Add an adjuvant to the spray solution. This product is not approved for use in California and some counties of Colorado (San Luis Valley).

Chlorsulfuron

Telar

Rate: 1 to 1.33 oz product/acre (0.75 to 1 oz a.i./acre)

Timing: Preemergence or postemergence to seedlings and rosettes.

Remarks: Chlorsulfuron has mixed selectivity, but is generally safe on grasses. Use a surfactant for postemergence applications. Chlorsulfuron is not recommended for late-season applications when the chances for rainfall for incorporation are low. The herbicide has long soil residual activity. Telar can be used near water, but cannot be applied to water.

Imazapic

Plateau

Rate: 8 to 12 oz product/acre (2 to 3 oz a.e./acre)

Timing: Postemergence to rosettes or bolting plants.

Remarks: Imazapic is will not injure most native grasses. It has mixed selectivity and tends to favor members of the Asteraceae and some grasses. It has some soil residual activity. Use a methylated seed oil surfactant at 0.25%. Imazapic is not registered for use in California.

Metsulfuron

Escort

Rate: 0.5 to 1 oz product/acre (0.3 to 0.6 oz a.i./acre)

Timing: Postemergence to rapidly growing plants up to early flowering.

Remarks: Metsulfuron has mixed selectivity, but is generally safe on grasses. Tolerance to metsulfuron increases as the flowering stage progresses. This herbicide applied at any stage has been found to reduce seed development. It can be tank mixed with 2,4-D. Use a surfactant.

Metsulfuron is not registered for use in California.

Dyer’s woad is also on the Opensight label (metsulfuron + aminopyralid) at 3.3 oz product/acre. However, this will provide only suppression and a second treatment may be necessary. The addition of 0.5 lb a.e./acre 2,4-D may improve control.

5. Citations

[1] Sheley, Roger L., and Janet K. Petroff. Biology and Management of Noxious Rangeland Weeds. Oregon State University Press, 1999.

[2] Edmonds, John. The History of Woad and the Medieval Woad Vat. U.K., Imperial-Purple, 2006.

[3] Washington State Noxious Weed Control Board. “Dyer’s Woad.” Nwcb.wa.gov, 2023, www.nwcb.wa.gov/weeds/dyers-woad.

[4] USDA. “Isatis Tinctoria.” Www.fs.usda.gov, www.fs.usda.gov/database/feis/plants/forb/isatin/all.html. Accessed 8 Jan. 2025.

[5] USDA. “USDA Plants Database-Isatis Tinctoria L.” Usda.gov, 2025, plants.usda.gov/plant-profile/ISTI. Accessed 10 Jan. 2025.

[6] Anderson, Lars W., et al. Weed Control in Natural Areas in the Western United States. Davis, California, University Of California Weed Research And Information Center, 2013.[7] King, L. J. “On the origin of the term” weed”.” Proceedings of the Indiana Academy of Science. Vol. 67. 1957.

teresaav, inaturalist.org

lorenzodotti, inaturalist.org

Fun Facts

Dyer’s woad contains the compound glucobrassicin, which is known for its anti-tumor properties. The plant is currently being studied for its protective effect against human breast cancer, fungal pathogens, and parasitic worms. The cultivation of dyer’s woad in Italy is yielding the possibility of extracting and mass-producing the beneficial compounds of dyer’s woad on a large scale. [4]