KKL-JNF Sets Out to Combat Ragweed in Israel

Monday, January 01, 2018

Since 2015, KKL-JNF has been an active member of a multidisciplinary team preventing further proliferation of Ambrosia confertiflora


Ambrosia confertiflora is an invasive plant, with the fastest proliferation rate of all the terrestrial invasive plants in Israel. Where did it come from, what kinds of damage can it cause, and how can you help in preventing its spreading?



Ambrosia confertiflora (Burr Ragweed) is suspected to have been brought to Israel in the 1990s unintentionally, as contaminants in bird and pond fish feed seed mixes imported from America to the Nablus area. The plant started spreading near Nablus and ultimately entered Emek Hefer (Hefer Valley) via the Alexander River and its tributary, the Nablus Stream. From Emek Hefer it continued to spread to additional sites, where it started to cover extensive areas. In recent years, authorities have gone to great lengths to stop its proliferation and the damage it causes to humans and the environment.

Ambrosia Confertiflora – Facts & Figures
Ambrosia confertiflora is an upright perennial herb 30 – 100 inches tall, which can be found mostly growing on stream banks and road sides. The ambrosia leaves are greyish-green, fresh all year long and with a distinctive scent, similar to tree wormwood. Its flowers are small, monoecious, and yellow or greenish. It blooms from September to October, and many people are very allergic to its bloom, so it has a very negative impact on health during these two months.

The Ambrosia is defined in Israel as an invasive species. Invasive species can be species of animals, fungi or plants transported by humans from other countries, intentionally or unintentionally. Some are brought over intentionally, to help in afforestation, stabilize soil, agriculture, or just as ornamental plants. While others were brought unintentionally, in various ways. When a foreign species invades and establishes itself in natural areas, it might displace native species and cause their extinction. The truth of the matter is that whether they arrived intentionally, or unintentionally, invasive species can cause tremendous damage and are considered the second main reason for species’ extinction globally.

The Ambrosia has the fastest expansion rate of all of Israel’s invasive plants. The Emek Hefer region is considered to have the worst ambrosia infestation. Wherever it invades it develops in dense stands and displaces native plants.

The greatest difficulty in eliminating ambrosia, on top of its proliferation speed, results from its quick regeneration, high resistance to herbicides - which require repeated application, as well as its varied methods of reproduction, both from seeds and plant fragments.

Methods of Dispersal
The plant is dispersed naturally as well as by humans.

Natural dispersal - the dispersal unit, i.e. the fruit, is a bur with 10-20 hooked spines enveloping a single seed. The spines cling to the fur of animals, and thus the seeds are dispersed. Dispersal also occurs via flowing water, especially during floods.

Dispersal by humans – when seeds or plant parts are unintentionally transported from one place to another by vehicles or agriculture machinery. Seeds or plant parts falling off tools are liable to create infestations in new locations where the ambrosia then grows, and grows and grows.

How can it Damage the Environment?
It turns out that this rapid invasive plant can cause much damage:

Agriculture – Ambrosia spreads quickly to agricultural groves, orchards and fields where it can cause severe damage to crops. In addition, the invasion of ambrosia to natural areas could displace nectar-producing plants and damage the honey industry, which relies on these wild plants.

Health – different species of ambrosia are highly allergenic, and cause tremendous suffering to millions of people worldwide. The damage caused by Ambrosia artemisifolia - an invasive species in Europe and a relative of the Ambrosia confertiflora- costs Europe 4.5 billion euro annually, mainly because of the Ambrosia’s highly allergenic pollen, which is dispersed by the wind, when in bloom, to great distances, causing great morbidity. The ambrosia’s health damage in Israel is estimated to cost the Israeli economy ILS 7M, and if its further proliferation in Israel is not prevented, the damage will be 4 times greater.

Biodiversity – the Ambrosia spreads quickly in natural habitats (mainly streams), creating dense cover that displaces the local plant species and completely changes the features of the ecosystems.

What can be done?
Since 2015, KKL-JNF has been an active member of a multidisciplinary team preventing further proliferation of Ambrosia confertiflora, which includes The Israel Nature and Parks Authority, The Ministry of Agriculture, The Ministry of Environmental Protection and Drainage Authorities. The team is engaged in mapping, disinfesting and monitoring. Nineteen additional Ambrosia invasion sites in their early stages were discovered in the forests of Israel’s central region and KKL-JNF is determined to make its eradication a top priority.

There is room for optimism. Half of the infestation areas spotted in the forests and sprayed 1-2 times in 2015-2016, had no sightings of renewed ambrosia in 2017. The treatment will be deemed successful only in those places where the plant won’t grow back within 5 years after the last treatment date. Until then the infestation sites are monitored and treated regularly by KKL-JNF forest rangers.

Want to Help Stop the Spread of Ambrosia?
If you’re riding your bicycle in the woods, hiking on the side of the road, spending an afternoon in the park or playground, and you see Ambrosia confertiflora - contact us, KKL-JNF, and tell us where you saw it. By doing so you will be helping to eradicate this invasive species so harmful to the environment. The earlier we locate a new site of infestation, the greater the chances of eradicating it with herbicides -at a lower cost.

If you happen to spot Ambrosia confertiflora weeds in a KKL-JNF forest, please contact Shani Gleitman, KKL-JNF ecologist at shanib@kkl.org.il. Please specify the coordinates or an accurate as possible location. And whenever possible also attach at least one photo.

If you’ve seen the plant or growth sites anywhere else, please report to omerk@npa.org.il according to the specified instructions in the Ministry of Environmental Protection’s announcement.

Edited and translated from the original article in Hebrew by Adi Blazar.
Scientific consulting and photography: Shani Gleitman, ecologist, KKL-JNF Forestry Division.
http://www.greenwin.kkl.org.il/features/environment/evironmental-problems/ambrosia/