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Integrated Management of Water Hyacinth in South Africa

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Integrated Management of Water Hyacinth in South Africa InTegraTed ManageMenT of WaTer HyacInth In South afrIca: development of an integrated management plan for water hyacinth control, combining biological control, herbicidal control and nutrient control, tailored to the climatic regions of South africa Marcus Byrne, Martin Hill, Mark robertson, anthony King, ashwini Jadhav, naweji Katembo, John Wilson, ryan Brudvig & Jolene fisher TT 454/10 Integrated Management of Water Hyacinth in South Africa: Development of an integrated management plan for water hyacinth control, combining biological control, herbicidal control and nutrient control, tailored to the climatic regions of South Africa. Marcus Byrne, Martin Hill, Mark Robertson, Anthony King, Ashwini Jadhav, Naweji Katembo, John Wilson, Ryan Brudvig, Jolene Fisher. Report to the Water Research Commission by University of the Witwatersrand, Rhodes University University of Pretoria WRC Report No. TT 454/10 JUNE 2010 Obtainable from Water Research Commission Publications Private Bag X03 Gezina, Pretoria 0031 SOUTH AFRICA [email protected] This report emanates from a project titled Integrated Management of Water Hyacinth in South Africa: Development of an integrated management plan for water hyacinth control, combining biological control, herbicidal control and nutrient control, tailored to the climatic regions of South Africa (WRC Report No. K5/1487). DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. ii EXECUTIVE SUMMARY Introduction Water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) is South Africa’s most damaging floating aquatic weed. Despite notable successes with the biological control of other floating aquatic weeds, and a concerted biological control effort against water hyacinth, its populations continue to reach newsworthy proportions on major rivers and dams. Hill and Olckers (2001) ascribed the variable success of the biological control programme on water hyacinth in South Africa to variable climatic conditions, eutrophication of aquatic ecosystems, interference from integrated control operations, the hydrology of infested systems and techniques for establishing biological control agents. The research presented in this report addresses the effect of temperature and nutrients on the growth of water hyacinth and some of its biological control agents and investigates the interaction of herbicide application with biological control. This has been done in light of discovering a sublethal dose of herbicide which will retain water hyacinth plants in a system to maintain populations of the agents. In addition, a management plan has been developed to guide water managers as what action should be taken in terms of combining biological control with herbicidal control under different climatic and nutrient conditions. Objectives To understand the current status of water hyacinth and its biological control agents in South Africa, under different climatic and nutrient conditions. To determine if low temperatures hamper the biological control of water hyacinth in South Africa. To examine the impact of nutrients on the biological control of water hyacinth in South Africa. To examine the feasibility of combining herbicides with biological control of water hyacinth. To develop methods for management of water hyacinth infestations, with a particular emphasis on remote sensing of water hyacinth. To develop a simple management plan that can be applied by water managers, to develop expectations of what is possible in terms of water hyacinth control within a given set of environmental conditions at an infestation site. Methods and Results Fourteen field sites were selected around the country to encompass the ecoclimatic range of water hyacinth. These were monitored monthly for two years, measuring both plant and insect parameters to evaluate their growth behaviour over a long time period. Temperature and nutrients were also measured at each site. Biological control agent numbers were shown to be low and adversely affected by frost and high nutrients. Nevertheless, the water hyacinth weevils were present and persisted at all sites, and some measure of control, as evidenced by a reduction in biomass, was recorded at most sites. However, sites were generally unstable iii having been disturbed by frost, flooding or herbicides. Most of the other biological control agents were generally absent from most sites. Although not tested in this project, this aspect concurs with Hill and Olckers’ (2001) hypothesis that the lack of correct release procedures has contributed to the variable success of the water hyacinth biological control programme. In an attempt to better integrated biological control with herbicide applications, trials were undertaken to determine a glyphosate dose which would stunt plant growth and reproduction, without harming three of the two weevils species, Neochetina eichhorniae and N. bruchi and the mirid, Eccritotarsus catarinensis. This dosage (0.8%) was then applied in the field, where measurements were taken of its effect on the plants, their nutrient status and populations of these three agent species. The herbicide varied between being benign to beneficial, to biological control insect populations, and promoted herbivory of the plants, while causing an increase in the carbon:nitrogen ratio of the plant tissue, which was expected to make the weed less palatable. High levels of nutrients did not reduce the stunting effect of the herbicide dose and did not adversely affect agent numbers. Non-target effects of the low dose of herbicide was investigated and it had no effect on the growth or survival of frog tadpoles, and water hyacinth alone was found to present a greater threat than any herbicide dose used in the experiment. It is recommended that herbicide be applied to recalcitrant water hyacinth sites as late in autumn as temperature will allow for that site, before the plants reproduce asexually by producing ramets; and again in spring, just as the new leaves are starting to develop and the plants add biomass by leaf elongation. Satellite imagery of selected field sites was used to test the hypothesis that remote sensing could be used for monitoring water hyacinth growth, as a tool to help decide when and where herbicide intervention should take place. Water hyacinth mats could be detected on small water bodies using multispectral imagery with a 10 m or less resolution. As much of this imagery is free it has potential to be used if regular, at least twice yearly, images are available. Failing that it is recommended that hyperspectral images be commissioned, and to that end the technique should be developed for water hyacinth so that the physiological status of the plant can be assessed as well as its physical extent. A site-specific management tool for controlling water hyacinth, an adaptive decision making framework was developed from local and international knowledge of the effects of the ecoclimatic conditions under which water hyacinth grows, and their effects on the efficacy of the biological control agents. Management decisions, such as the proportion of water surface that can be lost to water hyacinth, and the length of time available to allow biological control to take effect, are incorporated with herbicidal options to give a series of recommendations and expectations to water managers intending to control water hyacinth. Most importantly, biological control, maintained by active release of agents and their management by creation of refuges and use of low herbicide doses (generally accounted for by spray drift), is recommended for all levels of hyacinth infestation, except where complete eradication is required. iv Conclusions Water hyacinth remains a serious threat to South African freshwater bodies, but as a symptom of a larger problem of eutrophication, rather than a unique condition in itself. Biological control will be less effective and take longer under such circumstances, but will still provide a measure of control and is likely to eventually reduce weed biomass over a several year period. In the interim, glyphosate based herbicides can be used in an integrated manner with biological control, to maintain and encourage agent populations which will suppress the weed’s growth in summer. To this end, populations of biological control agents must first be actively and aggressively established in large numbers, and secondly reintroduced if they are lost due to flooding or frost. They must be maintained by providing refuges of unsprayed water hyacinth plants, or water hyacinth that has received a sublethal herbicide dose through spray drift. Ultimately nutrient inflows must be curtailed to cure this problem before the next new weed discovers South African water. Recommendations Water hyacinth infestations remain a symptom of nutrient enriched waters. Every effort should be made to ensure that South Africa aquatic ecosystems and in particular discharge water comply with the South African water quality guidelines. All available agents for water hyacinth should be correctly implemented at all sites of infestation. Herbicide should be applied to recalcitrant water hyacinth sites as late in autumn as temperature will allow for that site, before the plants reproduce asexually by producing ramets; and again in spring, just
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