Why is common milkweed dangerous, and how can you get rid of it effectively?

Common milkweed is an invasive, poisonous plant in Hungary whose rapid spread threatens native vegetation. A single mowing or removing it by hand is usually not enough to get rid of it, because it can resprout from its extensive underground root system. Lasting control is mainly achieved through targeted herbicide treatment, or a combination of mechanical and chemical methods, and for larger stands it can take 3–5 years. Over larger areas, successful control starts with an accurate survey of the infested stands – ideally by drone – followed by choosing the right control method and regular follow-up checks.

How did it reach Hungary?

Common milkweed (Asclepias syriaca) is a perennial plant that has spread across Hungary as an invasive species. In Hungarian it also goes by the names vaddohány ("wild tobacco"), selyemfű and papagájvirág. In the last century there were attempts to use it industrially, but these didn't live up to expectations – and in the meantime the plant became established in many parts of the country.

What does common milkweed look like?

You can recognise common milkweed by the following features:

• Stem: A tall plant with a straight, upright stem.
• Leaves: Large, arranged in opposite pairs on the stem.
• Flowers: Pinkish or purplish, grouped in rounded clusters.
• Milky sap: A milky sap may appear when the stem or a leaf is damaged.
• Fruit: A distinctive, elongated, plump pod that splits open when ripe.
• Seeds: Have long, silky hairs that help them spread on the wind.
• Flowering time: Usually flowers in summer, but the exact timing depends on the weather and site conditions.

Why does common milkweed spread so fast?

Common milkweed spreads through two complementary processes: the growth of its underground shoot system and the dispersal of its seeds by wind. The underground system lets an established stand creep into the surrounding area, while wind-borne seeds can reach entirely new places.

Vegetative spread underground

Common milkweed is a perennial, rhizomatous plant. It develops an extensive underground rhizome system from which new shoots can grow. This means that shoots that look separate at the surface are actually part of the same larger colony. Cutting the above-ground stems doesn't necessarily kill the underground parts, so new shoots may appear after treatment. Treating only what's above ground therefore often reduces the visible amount of the plant only temporarily.

Seeds can carry it long distances

The elongated, plump pod of common milkweed splits open when ripe and contains many seeds. The wind easily picks up the long, silky hairs on the seeds, so they can travel well away from the parent plant. If a stand sets seed, new infestation hotspots can form on top of the existing colony spreading.

That's why one aim of control is, wherever possible, to stop ripe seeds forming and scattering.

Preventing seed set alone won't eliminate an existing stand, however, because the plant can also spread without seeds through its underground shoot system.

It thrives on disturbed ground

Common milkweed establishes more easily where natural vegetation has been disturbed, plant cover is sparser, and there is more light or bare soil. Examples include fallow land, ground affected by earthworks, disturbed grassland, roadside and track-side verges, forest rides and forest edges.

Abandoned farmland and some types of sandy, drier habitats can be particularly favourable for it, but the species doesn't only occur on sandy soils.

Disturbance doesn't cause it to appear on its own, but it can help it establish and spread. In treated areas, it's therefore worth keeping an eye out both for milkweed returning and for other invasive species appearing.

Why is common milkweed dangerous?

As an invasive species, it can crowd out native vegetation

Thanks to its rapid vegetative spread, common milkweed can form dense, continuous stands. Within these patches, native plants may get less light, space and other resources, which can change the make-up of the plant community, with some species declining. Degraded grasslands, where the original vegetation is already weakened, can be especially vulnerable.

Its effects aren't limited to nature conservation: on farmland and other managed land, it can also make land use and maintaining the desired crop or vegetation harder. Some studies suggest the plant may also produce compounds that hinder the growth of other plants, although how much this matters ecologically can depend on the circumstances.

Even after common milkweed has been removed, there's no guarantee the original vegetation will recover quickly. In one Hungarian study, three years of mowing reduced milkweed cover, but the native vegetation did not regenerate and other non-native species appeared. Control is therefore not just a weeding job: longer-term management of the site and monitoring of its condition can also be important.

Is common milkweed poisonous?

Yes. The milky sap and other parts of common milkweed can contain toxic compounds, including cardenolides.

Contact with the plant can cause skin irritation or an allergic reaction, and eating it can be dangerous for both people and animals.

The risk of poisoning depends on the part of the plant and the amount eaten. In livestock, larger amounts can have serious, even life-threatening consequences.

The plant should therefore never be considered edible, and when handling it, it's sensible to wear gloves and avoid contact with the milky sap.

If it's a good honey plant, why does it need controlling?

Common milkweed can be a significant source of nectar, but that doesn't change the fact that in Hungary it is a non-native invasive species that can cause damage to nature and to land management. Its value as a nectar source for beekeeping therefore has to be weighed against the species' conservation and ecological impacts.

What is the legal status of common milkweed?

Common milkweed (Asclepias syriaca) has been on the list of invasive alien species of Union concern since 2 August 2017.

EU rules prohibit, among other things, intentionally bringing the species in, keeping, transporting, growing, propagating, placing on the market or releasing it into the environment, apart from the exceptions set out in the regulation.

In Hungary, Section 2 of Ministry of Agriculture and Rural Development Decree 43/2010 (IV. 23.) on plant protection activities (43/2010. (IV. 23.) FVM rendelet a növényvédelmi tevékenységről) specifically makes common milkweed subject to a mandatory control obligation.

In Natura 2000 sites, the specific requirements may also depend on how the site is designated and on the relevant nature conservation and subsidy rules.

How can you eradicate or control common milkweed?

Getting rid of common milkweed is particularly difficult, because the plant spreads not only by seed but also through its extensive underground creeping roots. Removing the shoots above ground is therefore rarely enough on its own: new plants can grow from roots left in the soil.

When choosing a control method, the main things to consider are the size of the infested area, the density of the stand and the conservation value of the site. Based on Hungarian conservation management experience, mechanical methods are mainly suited to limiting spread, while well-planned herbicide treatments can achieve lasting control of an established stand.

Hand-pulling and hoeing

Hand-pulling and hoeing are the simplest mechanical ways to tackle common milkweed. They involve removing the above-ground shoots, ideally together with part of the root.

This method is mainly an option when there are only a few plants or small, isolated patches on the site, or when herbicide use isn't permitted.

• Recommended stand size: Small hotspots of just a few plants.
• Ideal timing: Spring or early summer, before flowering and seed set.
• Expected result: Can help prevent seed spread, but usually doesn't eliminate the established root system.

The biggest limitation is that common milkweed's creeping roots can reach deep down and far sideways. New shoots can grow from root fragments left in the soil, and significant soil disturbance can help the plant spread further.

In an experiment on the Fülöpháza sand dunes in Kiskunság National Park, for example, shoots were removed by hand once or twice a year for four years on a 600 m² plot. Although the number of shoots fell from 4,047 in July 1994 to 1,140 in August 1997, the plant was not completely eradicated.

Removing the flower heads

If common milkweed has already appeared but removing the whole stand isn't feasible yet, removing the flower clusters by hand can reduce seed production and spread.

With this method, the flower clusters must be removed before the pods develop. Bear in mind, though, that common milkweed can flower again after treatment, so a single round is usually not enough.

• Recommended stand size: Small, scattered groups of a few plants.
• Ideal timing: At the start of flowering, before the fruit ripens, repeated if necessary.
• Expected result: Reduced seed spread, without eliminating the existing stand.

This approach can be particularly useful in protected areas where herbicide use is restricted. For large, dense stands, however, the manual work takes a lot of time.

Mowing and mulching

Mowing and mulching are mechanical control methods that can be used over larger areas too. The main aim is to remove the above-ground parts of common milkweed regularly, weaken the plant, and prevent flowering and seed set.

Mowing on its own can't be considered a reliable eradication method. Common milkweed's underground root system can survive treatment and produce new shoots.

• Recommended stand size: Larger, continuous patches and mowable grassland, even across several hectares.
• Ideal timing: First mowing before flowering, second after regrowth, in late summer or early autumn.
• Expected result: Lower shoot height and plant cover, but not necessarily complete eradication.

Hungarian conservation experience suggests that at least two treatments a year may be needed. At Hajós, for example, a 100-hectare infested area was mown twice a year for three years. As a result, milkweed cover fell to about a third and plant height halved, but the stand did not disappear.

At other sites, however, mechanical treatments led to increased resprouting and even to infested patches growing. Mowing is therefore mainly recommended for limiting spread.

The biggest advantage of mowing is that it can weaken the stand, which can make later herbicide treatment more effective.

Targeted herbicide treatment of the leaves

Based on Hungarian conservation trials, targeted herbicide treatment has proved one of the most effective methods for lasting control of common milkweed.

In these trials, the best results were mainly achieved with glyphosate-based products. For the treatment to work, it's particularly important that the active ingredient doesn't just damage the leaves but also reaches the plant's underground reproductive organs.

Leaf wiping and brushing

With leaf wiping, the herbicide is applied directly to the plant's leaves, so with careful application the amount reaching surrounding vegetation can be kept down.

This is especially useful in species-rich, near-natural grasslands where common milkweed occurs only sporadically and protecting the other plants is a priority.

• Recommended stand size: Small, isolated patches and scattered plants, especially in valuable grassland.
• Ideal timing: Late May to early June, before flowering begins. Resprouting plants can be treated again in July and August if needed.
• Expected result: Several years of consistent treatment can significantly reduce the stand.

Trials on the sandy grasslands around Győr showed that, when carried out properly, brushing was effective for controlling common milkweed. Its drawback is that it's labour-intensive: in the study it took on average twice as long as spot spraying.

Spot spraying

Spot spraying targets the identified milkweed plants or infested patches directly. This makes it possible to organise targeted control across larger areas, or areas made up of many separate patches.

• Recommended stand size: Small and medium-sized patches, and stands scattered across larger areas. It has also been used in dense, continuous stands, but there the risk of damaging surrounding vegetation may be higher.
• Ideal timing: The first treatment usually in May or early June, on young shoots with enough leaf area. Surviving and resprouting plants can be treated again in August and September.
• Expected result: A multi-year treatment programme can achieve significant control, but new shoots and seedlings mean further checks are needed.

Timing also depends on the weather. Conservation experience shows that strong sunshine, high temperatures and rain soon after treatment can reduce the effectiveness of some foliar-absorbed products.

Combined control for larger stands

For larger infestations spread over several hectares, a coordinated combination of mechanical and chemical methods is the right approach.

Mechanical treatments can, for example, limit seed set and in some cases reduce plant cover. Targeted treatment afterwards can then focus on the remaining or resprouting plants.

In practice, it's especially important not to plan treatment only for the continuous, clearly visible patches. Smaller stands in the surrounding area can become new seed sources.

Successful treatment may therefore require mapping infestation hotspots in advance, choosing methods area by area, and working together with neighbouring landowners or land managers.

Which common milkweed control method should you choose?

Method	Recommended stand	Ideal timing	Main aim
Hand-pulling, hoeing	A few plants, small hotspot	Before flowering	Reducing seed spread
Removing flower heads	A few scattered plants	Before the fruit ripens, repeated	Preventing seed production
Mowing, mulching	Larger, continuous patches	Before flowering, then after regrowth	Weakening the stand
Grazing	Grazeable grassland, assessed case by case	Regularly, depending on local conditions	Supplementary control
Targeted leaf wiping	Small patches, valuable grassland	May–June, with summer follow-up if needed	Lasting control
Spot spraying	Scattered and continuous infestations	From late spring, with late-summer/autumn follow-up if needed	Lasting control

Why are regular checks after control important?

Controlling common milkweed can take several years, and you can't judge success just by the shoots that have withered after treatment.

Some of the underground creeping roots can survive treatment, new plants can grow from seeds in the soil, and the site can be reinfested from the surrounding area.

Hungarian conservation management experience suggests planning for at least three years even for herbicide control, and for some stands a five-year treatment period may be better. After that, repeated checks and targeted treatment of any new plants are still advisable.

So the key to successful milkweed control is not any single method, but control matched to the level of infestation, the right timing and follow-up over several years.

On large sites, control starts with an accurate survey

In public spaces and small gardens, it's usually obvious fairly quickly where common milkweed has appeared. On forest, grassland or other near-natural sites covering several hectares, however, even an accurate survey of the infestation is a substantial task.

To plan treatment, you need to know where the plants or colonies are, how large an area is affected, whether there are isolated new hotspots, and where intervention is needed first. It also matters that the same patches can be found again during later checks.

Why are traditional field surveys difficult?

On large, dense or hard-to-reach sites, surveying on foot can take many working hours, full coverage is hard to guarantee, and scattered plants can be missed. Finding previously identified plants again on a repeat survey can also be a challenge. The larger the site and the more scattered the infestation, the more important it is to record survey results on a map.

How can drone surveys and AI-based species recognition help?

MainForest processes high-resolution RGB orthophotos taken by drone and analyses the images with its own AI-based system. Common milkweed is one of the invasive species we can currently detect automatically. Processing can assign GPS coordinates to the identified plants or infested patches, and the data can be used as a treatment map. Repeat surveys also make it possible to track changes on the site.

Accurate map data makes control more targeted: the people carrying out treatment can focus on the mapped infested points and patches, then return to the same locations for later checks. The technology doesn't replace expertise in the field or the decisions of the professionals responsible for treatment – it provides information that supports planning and follow-up.

Has common milkweed appeared over a large area?

MainForest's drone survey with AI-based species recognition can help map common milkweed plants and infested patches and assign GPS coordinates to them. The results can form the basis of targeted treatment and follow-up plans.

Ask the MainForest team for tailored advice on survey and control options!

Frequently asked questions about common milkweed

Are common milkweed and "wild tobacco" the same plant?

Yes, vaddohány ("wild tobacco") is one of the common Hungarian names for common milkweed (Asclepias syriaca). The name "milkweed" can also refer to other species, so the scientific name helps with accurate identification.

Is common milkweed poisonous?

Yes, the plant can contain toxic compounds. The risk depends on factors such as the part of the plant involved and the amount eaten, so it should never be treated as edible. Skin contact can also cause irritation.

Is mowing common milkweed enough?

No. Mowing can reduce plant cover and prevent seed set, but new shoots can grow from the underground vegetative system.

How long does it take to eradicate common milkweed?

Including follow-up checks, a rough estimate is around 3–5 years, but there's no timescale that applies to every site. Controlling an established colony may need treatment and checks over several seasons. The time needed also depends on the extent of the infestation, the site conditions and the methods that can be used.

Why does it come back after control?

New shoots can grow from underground parts left in the soil, new seedlings can appear, and on large sites some infested patches may be missed during treatment. That's why regular follow-up checks are important.

Can you plant common milkweed?

No. Common milkweed is an invasive species of Union concern, so EU rules prohibit, among other things, intentionally growing it, propagating it or releasing it into the environment.