THE ROLE OF BIOCONTROL IN INTEGRATED WEED MANAGEMENT

Authors: Center, Ted; Van, Thai; Pratt, Paul; Tipping, Philip; Rayamajhi, Min; Franks, Steven; Dray, F Allen

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2003
Publication Date: 11/5/2003
Citation: Center, T.D., Van, T.K., Pratt, P.D., Tipping, P.W., Rayamajhi, M.B., Franks, S.J., Dray Jr, F.A. The role of biocontrol in integrated weed management. Meeting Abstract.

Interpretive Summary: We draw on two examples of integrated weed management, one negative and one positive, involving waterhyacinth (Eichhornia crassipes) and melaleuca (Melaleuca quinquenervia). Integrated control of waterhyacinth was never attempted, although fortuitous incidences have occurred; in contrast, a management plan was developed to integrate biological, herbicidal, and mechanical control measures against melaleuca. For the unplanned waterhyacinth example, we contrast managed sites, where herbicides were the principal control measure used, with unmanaged sites, where no deliberate control measures were used but where passive biological control was operative. Herbicidal control suppressed both weed and waterhyacinth weevil populations. Herbivore-impacted infestations at unmanaged sites showed low growth potential. Reproductive status of the weevils improved with increased plant quality at managed sites, and declined as herbivory increased. Excellent plant quality at managed sites enhanced plant growth and flowering and the improved host quality induced reproductive vigor of the weevils, but ensured weed regrowth and the need for future control. This suggests an integrated approach might be appropriate; using herbicides to maintain waterhyacinth infestations below management thresholds but in a manner that conserves bioagent populations. In the case of melaleuca, it was acknowledged during planning that insects could not remove the massive biomass associated with stands of large trees. An interagency-developed plan called for traditional controls to remove trees from critical areas while awaiting development of biocontrols. The later introduction of these agents reduced invasiveness of remaining trees. Herbivory resulted in reduced seed production, diminished seedling recruitment, increased seedling and sapling mortality, gaps in melaleuca canopies, and increased plant diversity. Herbicidal and mechanical controls, which are no longer necessary in many areas, can now be used at leisure to remove neutered stands of remaining trees. This demonstrates the utility of a well planned management program that capitalizes on the strengths of each type of control tactic.

Technical Abstract: We draw on two examples of integrated weed management, one negative and one positive, involving waterhyacinth (Eichhornia crassipes) and melaleuca (Melaleuca quinquenervia). Integrated control of waterhyacinth was never attempted, although fortuitous incidences have occurred; in contrast, a management plan was developed to integrate biological, herbicidal, and mechanical control measures against melaleuca. For the unplanned waterhyacinth example, we contrast managed sites, where herbicides were the principal control measure used, with unmanaged sites, where no deliberate control measures were used but where passive biological control was operative. Herbicidal control suppressed both weed and waterhyacinth weevil populations. Herbivore-impacted infestations at unmanaged sites showed low growth potential. Reproductive status of the weevils improved with increased plant quality at managed sites, and declined as herbivory increased. Excellent plant quality at managed sites enhanced plant growth and flowering and the improved host quality induced reproductive vigor of the weevils, but ensured weed regrowth and the need for future control. This suggests an integrated approach might be appropriate; using herbicides to maintain waterhyacinth infestations below management thresholds but in a manner that conserves bioagent populations. In the case of melaleuca, it was acknowledged during planning that insects could not remove the massive biomass associated with stands of large trees. An interagency-developed plan called for traditional controls to remove trees from critical areas while awaiting development of biocontrols. The later introduction of these agents reduced invasiveness of remaining trees. Herbivory resulted in reduced seed production, diminished seedling recruitment, increased seedling and sapling mortality, gaps in melaleuca canopies, and increased plant diversity. Herbicidal and mechanical controls, which are no longer necessary in many areas, can now be used at leisure to remove neutered stands of remaining trees. This demonstrates the utility of a well planned management program that capitalizes on the strengths of each type of control tactic.