Hướng dẫn sử dụng, và Cơ khí Phương pháp dự phòng 14,1 GIỚI THIỆU Phương pháp dự phòng, hướng dẫn sử dụng, và cơ khí tạo thành một liên tục của các phương án quản lý thực vật. Tránh các vấn đề phiền toái thủy sản được ưa chuộng nhất, do đó các biện pháp phòng ngừa là cần thiết. Nếu nhiễm mới các nhà máy gây khó chịu được tìm thấy, nếu chỉ có các khu vực nhỏ của các nhà máy thuỷ sản cần phải được quản lý, phương pháp thủ công có thể thích hợp. Nếu phiền toái đã. | 14 Preventive Manual and Mechanical Methods INTRODUCTION Preventive manual and mechanical methods form a continuum of plant management options. Avoiding aquatic nuisance problems is the most desirable so preventive measures are needed. If new infestations of nuisance plants are found or if only small areas of aquatic plants need to be managed manual methods may be appropriate. If a nuisance is already large and can t be managed manually then mechanized plant removal is an option or can become part of an integrated aquatic plant management program. Contingency planning cannot be overemphasized. To paraphrase Benjamin Franklin a gram of foresight prevents a metric ton of milfoil. Typically aquatic plant invasions have been unnoticed or overlooked until they become problematic. Contingency planning for exotic invasions is similar to planning for other natural disasters. The threat is identified and the resources for dealing with it including people equipment and finances are known and can be deployed quickly and easily. Barriers to rapid action such as the need for permits or legislative approval are taken care of ahead of time. Preventive manual and mechanical approaches form part of the armory of techniques available to manage aquatic plants. PREVENTIVE APPROACHES Many aquatic plants have large ranges and are spread naturally by birds wind and water current Johnstone et al. 1985 . Many exotic and nuisance aquatic plants spread vegetatively. Natural dispersal of whole plants or long-stemmed fragments long distances is unlikely Johnstone et al. 1985 . As examples whole plants of water hyacinth Eichornia crassipes were found in a wastewater treatment pond and waterlettuce Pistia stratiotes was found in a stream in northern Wisconsin during the summer of 2002 Frank Koshere Wisconsin Department of Natural Resources WDNR personal communication 2002 . It is unlikely that birds wind or water current carried these plants all the way from the southern United States
