This research project compared the sensitivity of two cultivated plants to a broadband herbicide with the sensitivity of the two wild varieties and of two other closely related wild plants. Based on a vegetative growth test according to OECD guideline 227 effects of the pesticide on the test plants were assessed. The tested application rates ranged between one and thirty percent of the actual application rate. The broadband herbicide “Roundup® Ultra Max” by Monsanto, containing 450 g/l of its active ingredient glyphosate, was used. A maximum field application rate of 1800 g ai/ha was assumed. Besides the potential impact on plant growth, effects on seed production and the capability to compensate previous adverse effects were determined in a lifecycle test lasting 98 days. Seeds produced during the lifecycle test were harvested, dried and sown again in order to assess the germination capacity of the F1 generation.

The intensity of pesticide caused effects varied between crop species and their wild relatives. In general the responses to pesticide treatment indicated a higher sensitivity of wild plants. Application rates corresponding to a pesticide drift rate of 4 – 9 % caused a growth reduction of up to 50 % in wild plants, whereas the two tested crop species did show such an extensive effect not until they were treated with concentrations corresponding to 15 % drift rate. Strong differences in the response between species of the same family prevent the appreciation of single species as representatives of higher taxa. The results provide evidence that morphological characteristics, as e.g. leaf surface texture, are better indicators of plant sensitivity then taxonomic relationships.

The results of the life cycle test demonstrated that plants were able to compensate previous adverse effects on younger developmental stages. Successive height measurements indicated that test plants could recover from adverse effects induced by up to 5 – 17 % pesticide drift rate. However, negative effects on young developmental plant stages caused by 5 % pesticide drift resulted in lower seed productivity and reduced germination capacity of the F1 seeds.
This study showed that the pesticide Round up® represents a threat to the diversity of natural boarder-vegetation, due to its negative effects on growth and seed production of wild plant species. As a consequence, it is suggested to consider the use of relevant wild plant species in standard tests assessing toxicological effects of pesticides.

Poster as presented at the SETAC GLB annual conference 2009