| Popis: |
In the temperate zones, defined as lying between latitudes 35° nd 60° N and S, most submerged weed problems are caused by mixed plant communities and require a general, water bound herbivore, e.g. grass carp, or a number of host-specific organisms to avoid a predominance of resistant plants developing. A successful bio-control agent must be able to survive the low temperatures of winter and except for those occurring at high altitudes, tropical and subtropical organisms cannot be used. The answer must be sought in temperate and fringe areas. The search should range beyond conventional biological control and include the indirect encouragement of natural enemies by for instances restricting their parasites and predators and also the study of all aspects of plant competition including allelopathy. Much more research effort is needed but until new methods have been developed to replace them it would not be wise to discard established practices. |
