Epsilon Archive for Student Projects

Abstract

Herbicide resistance is the result of an evolutionary process where a population gradually changes from being susceptible to being resistant to an herbicide. The resistance mechanism is usually a change in the biochemistry of the weed, but in some cases changes in morphology or growth rhythm. The change is caused by random mutations. Two resistance mechanisms are found in black-grass; target site resistance and metabolic resistance.

Black-grass is a tufty, winter annual grass weed, which is mainly found in milder climates. Black-grass is a big problem in Southern Europe. In Sweden, it has its main extension in Skåne, Öland and Gotland.

Herbicide resistance is increasing on a global level, especially in farming systems that strongly rely on chemical spraying. Four major factors affecting the build up of resistance are; length of life cycle, spreading, methods of weed control and also the seed bank in the soil. Integrated weed management is required for long-term control of black-grass. A varied chemical spraying should be complemented by other methods, e.g. in crop rotation and tillage methods, increased mechanical methods, clean machines etc. It’s important to alternate between different modes of action, since one reason for increased resistance is that the same herbicide or a few modes of action recurs frequently.

There are several methods for testing herbicide resistance. This thesis includes a germination test in petri dishes. Four herbicide from different herbicide groups are tested in seven populations of black-grass, from three different countries. The experiment is a part of a comparative study between laboratories in several Nordic and Baltic countries. The evaluation of the test includes three methods; visual assessment of the coverage, frequency of the number of shoots over 1 cm and a dry matter test. The herbicides are; fenoxaprop-P (in the herbicide Event Super), cycloxydim (Focus Ultra), sulfometuron (Oust) and pendimethalin (Stomp).

The result matched with the expected resistance level for some of the populations and herbicides, but not for all. This may be due to experimental mistakes. A repeating of the test would be optimal, to secure more accurate conclusions about the robustness of the test.

Through this work I have come to the conclusion that it’s difficult to find a robust and fast method to detect metabolic resistance. Seed tests to detect target site resistance are often good, but as metabolic resistance usually occurs later in plant development, dose-response-tests in pots are preferred.