Annual dormancy patterns of weed seeds influence weed control

Dormancy of buried weed seeds is not stable but fluctuates in an annual pattern. Tests of exhumed see ds at a range of temperatures have shown that relief of dormancy is characterized by a widening of the range of temperatures over which germination can occur, during induction of dormancy this range becomes narrower. Temperature in the field plays a dual role. On the one hand, germination depends on whether the actual temperature is within the germination temperature range. On the other hand, annual fluctuations in temperature are the main driving force for the changes in dormancy. A model was developed that simulated the annual changes in dormancy. The value of descriptive models for the understanding of the behaviour of weed seeds in soil is discussed. Apart from the successful stimulation of Striga seed germination in soil by infusion of ethylene, other attempts to reduce seed banks by chemical methods have failed. Nitrate is the major naturallyoccurring soil component that stimulates seed germination. It widens the annual period that seeds can germinate.