3. Reasons for relatively slow popularity and adoption of biological weed control

Recent research activities and weed control practices around the world have shown that the old idea derived from untested opinions; that biological approach to weed control is usually very slow, unpredictable, expensive and mostly unsuccessful is totally not true. Apart from the high initial costs, biological approach to weed control has been known to be relatively cheaper when compared to other methods; however certain factors have slowed down the rate of adoption. These factors include: long time of establishment-usually 20 years or more to ensure success, inadequate or no records of the extent of pre-biological control weed infestations that should serve as a guide for a new biocontrol program, discouraging story of poorly implemented weed bio-control programs. A lot of success stories however have been documented [35]. Lack of information about previous successfully implemented biological control of weeds often lead to untested theories becoming established dogma and this negatively influence the decisions to or not apply it [36]. For instance Mcfadyen [35] stated that it was believed that biological control of trees is difficult, but many examples of trees controlled by insects have been reported [37, 38]. Also classical biological control has been viewed as unsuitable for weeds of annual crops or other frequently disturbed environments [39, 40], however there are many examples of successful control of crop weeds [41, 42].

Some researchers have reported that there are evidences showing that some agents introduced for exotic weed control have attacked non target, native plants [43, 44]; and this situation has raised concerns among biological control workers and weed scientists as well as the governments [5, 43, 45, 46]. Opposition to biological approach to control of weeds has also contributed to slowing down the rate of adoption and practice; this is because some researchers and weed control scientists believe that it is difficult to estimate the cost or the feasibility of biocontrol [47]. Based on a study carried out in South Africa, it was reported that some of the weed biocontrol projects have provided practical solutions to problems e.g. the development of Stumpout for the treatment of wattle stumps and the use of C. gloeosporioides for the control of H. sericea. However other projects have been less successful and have resulted in the rejection of potential agents for various reasons and these include C. albofundus on A. mearnsii, X. campestris on M. aquaticum and G. nitens on R. cuneifolius [48]. Vurro and Evans [49] identified legislative hurdles, technological and commercial constraints as limitations to the adoption of biological weed control in Europe. Olckers [50] stated that limited budgets in many countries have also helped to slow than the rate of adoption and practice of biological approach to weed control.
