The impact of mowing on the growth and blooming of common ragweed (Ambrosia artemisiifolia)

Abstract

Common ragweed (Ambrosia artemisiifolia) is an invasive alien spe- cies originating in North America that has spread widely in Europe in last decades. Removal of common ragweed and prevention of its reproduction is mandatory for landowners in Slovenia, decreed by Slovenian legislation. One of the most commonly used removal methods is mowing, so we decided to conduct a research project on the impact of mowing on the growth and propagation of this species. We used the common ragweed plants that we collected in the spring at the road embankments and planted them in plastic box planters. At the beginning of the summer, we cut the plants at three different heights, which represented a mowing at three different heights. A group of plants was left untreated and represented a control group to compare with the test plants. We monitored their growth until the end of September, by measuring the height of plants, the development of male inflorescences, where allergenic pollen is produced, and seed development. We found out that the survival rate of the plants cut above the first pair of leaves were affected the most, while all the plants cut above the third pair and plants of the control group, survived. Plants of control group reached largest height and produced the highest dry mass as well. Contrary to expectations, differences in height and mass of test plants were negligible. Mowing has a major impact on the development of male inflorescences. Mowing above the 1st and 2nd pairs of leaves has reduced the overall length of male inflorescences to a third, while mowing above the 3rd pair almost halved the length of inflorescences. That resulted to a significant reduction in the amount of allergenic pollen. Altogether, most of the fruits (achenes) have grown on control plants. If we calculate the average number of fruits per plant, on average most fruits have developed on control plants and plants cut the lowest. We may conclude that a single mowing in a season does not reduce the production of seeds, which is an important information for maintainers of public areas as well as landowners.