Ambrosia artemisiifolia ('ambrosia') is an invasive weed in Europe, important not only for its detrimental effects on agriculture and nature but, even more, on human health. Ambrosia pollen is highly allergenic. To provide European countries with a scientific basis to implement national strategies for ambrosia prevention and control, this project set out to carry out trials in greenhouses and fields to find the best possible control options fitting different scenarios. The control options focused upon were herbicide and mechanical treatments and the effect of competition with other plants. Any strategy must aim to prevent not only pollen production but also production of fertile seeds. Ambrosia can only be eradicated, with reasonable means, from sites where it has not yet infested the soil seed bank. Different habitats give different opportunities for control:

-Agricultural fields: Herbicide treatments can be split for improved efficacy. Some herbicides are less effective with increasing plant size. Herbicide efficacy will also be enhanced by competitive crops or mechanical weed treatments. Organic farmers should explore these non-chemical options.

-Construction sites: Bare soil should be avoided by establishing a dense plant cover. This will prevent mass invasion of ambrosia and thus make manual eradication of single invaders possible (plants to be uprooted and destroyed before flowering).

-Roadsides: Sites heavily infested by ambrosia should be herbicide-treated after mowing to achieve the best control of plant re-growth.

-Gardens and parks: Bare soil should be avoided by establishing a dense plant cover. Single plant stands should be eradicated by hand.

-Natural habitats: Disturbed soil should immediately be covered by a dense population of native plants in case of an advanced infestation. Single plant stands in areas where infestation is beginning, should be uprooted and destroyed. If ambrosia is growing in competition with other plants, mowing can be tried as a control method.

Ambrosia has exceptional potential for regrowth after cutting: side-shoots grow vigorously to flower and produce seeds if not controlled. This limits the effectiveness of mowing in general. Special attention must be given to infested stubble fields. The project established an informal network of researchers working with invasive weeds. This network will be kept alive in the short run through the writing of the planned papers, and in the longer run through the newly formed International Ragweed Society. An illustrated brochure with suggested practical guidelines for ambrosia control was prepared in several languages (Danish, English, French, German and Slovene). Thus we hope to facilitate swift accommodation and implementation of guidelines for 3/69 ambrosia control and prevention all over Europe, according to national policies and priorities, and guided by scientific knowledge.