The role of seed ecology in improving weed management strategies in the tropics

Weed seed banks reflect past weed populations and management practices and are the source of weed infestations to come. The factors affecting weed seed germination, however, are often poorly understood. Depleting the soil seed bank and influencing germination patterns are common goals of enduring cultural weed management practices. Greater understanding of the factors influencing the germination of weed seeds could facilitate the development of more effective cultural weed management practices through either suppressing germination or encouraging germination at times when seedlings can be readily controlled. Such cultural methods may contribute to overcoming problems such as feral crops (e.g., weedy rice), crop volunteers, and the evolution of herbicide resistance in weeds that have, in some systems, increased to a point where the lack of sustainable practices is a threat to productivity. Weed seed germination is commonly influenced by light exposure, soil moisture, burial depth through tillage, the use of mulches, fire for land clearance, and flooding of the soil. Harnessing these factors to influence germination can serve as major entry points for improved weed management. Diverse crop production systems provide a wide range of examples to illustrate how recent advances in the understanding of the responses of weed seed germination can be used to develop new and sustainable cultural management of weeds. Crop management practices, such as adopting no-till crops or delaying tillage, that increase weed seed exposure to predators (ants, beetles, etc.) could be incorporated into integrated weed management programs. Retention of crop residue on the soil surface under no-till systems can suppress weed seedling emergence, delay the time of emergence, and allow the crop to gain an advantage over weeds, and reduce the need for control. Rotation of tillage or crop establishment system could also be adopted to deflect the "trajectories" of likely weed population shifts. In rice, flooding after herbicide application or hand weeding can largely prevent the growth of weeds and reduce the need for further interventions