Ambrosia confertiflora is a major threat to crops, public areas and local shrubbery.
By Zafrir Rinat | Jul. 2, 2015

The invasive weed Ambrosia confertiflora was not known in Israel two decades ago. But in recent years it has become a major threat to agricultural crops, public areas and natural shrubbery. So much so that the Environmental Protection Ministry and Nature and Parks Authority have put together a national plan to combat its expansion.

The authorities began implementing the plan this week in the Emek Hefer area, where the weed’s invasion is especially harmful.

Under the plan, nature authority officials will locate ambrosia expansion hubs in the Motza, Sorek Stream and Binyamina regions and stop the expansion by shearing, pruning and spraying.

The plan was drawn up with the help of ecological adviser Roy Federman and Dr. Jean Marc Dufour-Dror, a specialist on invasive alien plants, or species that are not native to the ecosystem, and which may cause economic or environmental harm or adversely affect human health.

Ambrosia seeds are suspected to have entered Israel as contaminants in seed mixes for feeding birds and pond fish imported from North America in 1990 by farmers in the Nablus area. The plant, a species of ragweed, started spreading near Nablus and ultimately entered Emek Hefer via the Alexander spring and its tributary, the Nablus stream.

The weed develops in dense stands, crowding out and suppressing native plants, thus entirely altering the ecosystem. Eventually it invades citrus groves and avocado plantations, causing serious damage.

Ambrosia also produces a large amount of severely allergenic pollen, causing hay fever and other allergies in susceptible people.

If ambrosia seeds are found in Israeli farming produce, the authorities fear, it will be difficult to export it to European countries where the weed has not been discovered yet.

Sharon Drainage Authority officials were the first to detect the weed’s expansion and sprayed it along the Alexander stream. In the last two years the Emek Hefer Regional Council has employed a team to combat the invader, headed by local resident Yehuda Geller. The local water association has been helping farmers who are cooperating to stop the weed’s invasion.

Geller says the ambrosia is spreading from the Alexander stream and farming fields into communities. He points out places where the weed is growing in abandoned cowsheds and private gardens. Near the Alexander stream the weed has replaced the grass that was supposed to serve hikers and visitors. Its seeds have entered the Sharon communal settlement of Bat Hefer, after a flood of rainwater from the Nablus stream.

“We spray several times a year but it doesn’t solve the problem entirely,” says Geller. “There are still seeds in the ground that renew the growth. If farmers or visitors drive past, their cars spread the seeds to other places. We’ll have to continue the work for years until the seed reserve dwindles,” he says.

Stopping the weed’s expansion is difficult in a region with numerous communities like Emek Hefer. Spraying near residential areas is tricky and some infested areas cannot be treated because their owners are unknown and it is hard to get a permit to work in them.

“We receive dozens of calls reporting the ambrosia’s presence, which means there are many people who aren’t at all aware the weed is in their back yard,” says Geller.