Project on the Eradication of the Weed Wedelia trilobata from Niue. Pest Management in the Pacific Programme

Transcription

1 Project on the Eradication of the Weed Wedelia trilobata from Niue Pest Management in the Pacific Programme (Component 7: Cook Islands, Niue and Tokelau) Progress Report INTRODUCTION Wedelia trilobata (L.) is an attractive creeper with its yellow flowers and glossy leaves. It is also an important invasive weed in several Pacific Island Countries. In Niue, the distribution of the weed remains limited to gardens and roadsides, although at some places it has commenced invading plantations and secondary forests. In view of the impact of the weed in other Pacific Island Countries, the Niue Department of Agriculture, Forestry and Fisheries is determined to eradicate the weed and has requested SPC for assistance to achieve this objective. With assistance from the Secretariat of the Pacific Community (SPC), an eradication programme was started in the first week of March 2001 (27 February - 8 March). Locations of the weed were identified and demarcated, measured and sprayed with a solution of Round Up (a.i. glyphosate; at 10ml/l) which was applied by knapsack sprayer. Simultaneously, public awareness was raised through a TV interview (both in English and Niuean), and by placing signboards at strategically located major sites around the island. A survey at the start of the eradication campaign showed that Wedelia was present in a total of 35 sites in 11 villages. Twenty-two of these were located near residences, while the remaining sites were at roadsides in or near villages. The consultant recommended a second visit to take place some 3 weeks later to monitor progress of the eradication campaign, and to assess the impact of Round Up on the weed. More specifically, the following Terms of Reference were addressed: 1 Monitor the progress of the eradication programme of Wedelia trilobata, and evaluate its suitability for Niue conditions; 2 Assess the impact of the spraying programme that was commenced in the first week of March;

2 3 Determine the progress in developing community awareness materials (e.g. leaflet, signposts and TV/Video information materials); 4 Provide recommendations to enhance the ongoing eradication programme and increase its effectiveness; 5 Propose a programme for the continuation of the eradication campaign of Wedelia; and 6 Advise on measures aimed at eradicating other invasive weeds that have been identified as suitable targets in recent surveys. The Consultant visited Niue from March This document reports on the consultant's findings. IMPLEMENTATION OF THE CONSULTANCY The eradication programme started in early March was continued by DAFF staff, under supervision by Mr. Tom Misikea, Project Coordinator, with assistance from Mrs. Crispina Konelio, Senior Quarantine Officer. Implementation of slashing and spraying was delegated to the Department's Extension Service, which supervised 2 labourers hired from project funds. The consultant visited all sites that had been treated with herbicide and assessed the impact on the weed. 1 Progress of the eradication programme of Wedelia trilobata, and its suitability for Niue conditions Number of Wedelia infested sites: Since the airing of the TV interview, 11 new sites have been reported to DAFF, bringing up a total of 46, with a coverage of 12,747 sq m. All have been visited, measured and appropriate control measures determined for each site. Slashing had been applied at two sites to reduce weed cover and facilitate application of herbicide (Appendix 1). Spraying of sites: Sprays of Round Up (10 ml/l) were applied until 23 March to 12 Wedelia sites, when stocks of the herbicide became critical. During the last week, Round Up (10 ml/l) mixed with a solution of Urea (30 gram/l) to enhance the impact of the herbicide on the weed, was applied to 6 sites. Following depletion of Round Up stocks, Gramoxone (a.i. paraquat) was applied by knapsack sprayer at a rate of 100 ml/15l from 26 March: 3 sites were sprayed, as well as 2 sites where the impact of earlier sprays of Round Up was considered unsatisfactory.

3 2 Assess the impact of the spraying programme that was commenced in the first week of March Application of Round Up (10 ml/l) to densely weed infested areas reduced Wedelia cover by an estimated 50-70%. While a better result was expected, the likely causes for this were an insufficient volume of the herbicide applied to the area, as well as heavy rainfall within several hours after application. In some places (Alofi South), leaves and young stems had been killed by the chemical, but young leaf growth was already observed on nodes of older stems. At sites with low weed cover, notably those where the weed had invaded lawns and in mowed areas near roadsides, similar rates of Round Up were observed to produce very high mortality rates. Application of Gramoxone (paraquat;100 ml / 15 litres) applied after stocks of Round Up had been depleted showed immediate effects on the weed. The fact that this weedicide only requires a short period of a few hours of dry, sunny weather following its application to achieve its maximum impact, makes this herbicide very suitable for use in areas with dense weed cover. Application of a single spray not only produced severe defoliation but also killed many (green) stems. Also, as sprayed areas became clearly visible to the public, it will undoubtedly contribute to increasing public awareness on the campaign. Slashing of weeds 1-2 weeks before applying herbicides reduced spraying time and spray volume in areas of dense weed cover. It is recommended to continue this practice. 3 Determine the progress in developing community awareness materials (e.g. leaflet, signposts and TV/Video information materials) A draft of the information leaflet on Wedelia and the ongoing campaign has been prepared in English and Niuean, and is currently circulated among DAFF staff for comments. Niue DAFF is also awaiting arrival of suitable printing paper before commencing printing of the leaflet. for distribution among the public. A further 6 signposts have been erected at strategically located sites, bringing up a total of 9. Placing of a further 3 sign posts is planned in the forthcoming weeks. Mr. Shane Tohovaka, of the Broadcasting Corporation of Niue (BCN) has prepared a script for a 3-5 minutes video production on Wedelia (Appendix 2). An indicative budget of NZD has been mentioned as a guideline for production cost. The video can be considerably improved if footage of the weed's coverage and impact from Fiji (Rewa delta) can be included; the AV department of SPC, Nabua, Fiji will be requested to provide such footage. In the meantime, Niue DAFF will continue to collaborate with BCN to produce the video, which will be ready for distribution and broadcasting within 2 months after receipt of funds.

4 4 Provide recommendations to enhance the ongoing eradication programme and increase its effectiveness 5 Propose a programme for the continuation of the eradication campaign of Wedelia Application of herbicides: Application of Round Up at recommended rates (10 ml/l), preferably mixed with 30 g/l of Urea is adequate to control Wedelia in areas of low weed cover. Site inspections are required after 3-4 weeks to assess the impact of the spray, and apply a second dose to surviving plants if needed. Further monthly inspections of sites are required for a duration of at least 6 months. Slashing of areas with dense weed cover at 1-2 weeks prior to applying the herbicide is very useful and reduces spray volume and time required to spray the area. It is likely that this also enhances the impact of the herbicide. Application of paraquat is very useful in areas of dense weed cover, even if they have already been slashed, as it further reduces the weed cover. It will also increase the impact of Round Up application some weeks later. Also, weeds killed by paraquat become dry and allow controlled burning of the area, which further reduces weed cover and regrowth. Seedlings: Care should be taken to check not only for regrowth but also for seedlings that may have germinate after reduction of weed cover. Notes should be made on their presence and density to provide details which can be used to assess generative reproduction rates of the weed and the presence of a seed bank in the soil, if any. Herbicide (Round Up) should be applied once the seedlings have reached a height of about 5 cm. Public awareness: Another interview with BCN should be arranged for the first week of April, to maintain the level of public awareness. The interview should focus on the progress of the current programme and its achievements, and mention the development of the information leaflet and video programme. The signposts are very effective as they continue to convey a clear message concerning the programme to the public. SPC Assistance: Further funds ( NZD) may be required to sustain the current campaign and support production of information materials. A follow up visit after 3-4 months by the consultant is advisable to monitor progress of the eradication campaign and provide support to maintain its momentum. The visit would also be appropriate to discuss support for programmes aimed at eradication of other invasive weeds.

5 6 Advise on measures aimed at eradicating other invasive weeds that have been identified as suitable targets in recent surveys Chain-of-Hearts, Antigonon leptopus During the consultant's last visit, 2 plants of Chain-of-Hearts, Antigonon leptopus, were removed from the premises of the Waimanu Guest House, Alofi South. The roots and tubers of one plant were dug up and incinerated. Inspection indicated however that regrowth consisted of 3 vines, each of approx. 1 m length from one plant, whereas 11 new shoots had grown from the site where the roots of the plant were thought to have been removed. One morning was dedicated to cutting the vines and clearing the ground at a heavy infestation of Chain-of-Hearts behind government housing opposite the hospital. Roots and tubers of the many vines were left in the ground, but vines were removed between ground level and m height. As the weed does not produce aerial roots, it depends on its survival on nutrients and water supplied by roots in the soil. The following day the foliage of the weed - which fully covered a Barringtonia tree - was observed wilting. Regular (2 weekly) inspection of the area is needed, and sprays of Round Up should be applied to kill the tubers and sprouts, to achieve control the weed. The Chain-of-Hearts weed is only known from a few other sites (approx. 5) in Alofi, and its eradication should not be problematic. The site with the largest infestation of the weed is near the hospital, where it has overgrown Leucaena trees near the roadside covering an estimated area of 30 sq m. Treatment should include cutting down the Leucaena trees, removal of vines for incineration, and spraying of the area with Round Up or paraquat. Infestations consisting of only a single or few plants should be treated by removing the complete vine, roots and tubers. Regular inspections and herbicide applications are needed at all sites to ensure eradication efforts will be successful. Scindapsus aureus This vine was likely introduced as an ornamental a number of years ago. It spread mainly from discarded cuttings: Dispersal by seed seems to be negligible. Its capabilities for rapid growth in partial and full shade has enabled it to become established at the fringe of forested areas, from where it has commenced its invasion. The weed is generally present in and around urban areas, but a small patch was observed along the main road inside the Huvalu rainforest reserve. Eradication of this weed may still be possible, particularly if it is supported by an intensive campaign to increase public awareness and support. Current awareness on invasive weeds among the public is high levels, as a result of the Wedelia and Mimosa eradication campaigns, which increases the chances for eradication of S. aureus from Niue. However, considerable funds are needed to fund labour, equipment, herbicides and transport. Any eradication programme of

6 this weed should commence immediately before the weed spreads further into primary and secondary forests, and chances of its successful eradication become considerably smaller. The Department of Agriculture views the eradication of this weed as a priority, and appears to have extensive support from the public in this. Wood Rose, Merremia tuberosa The Wood Rose is another vine which is a serious threat to forestry and the environment in Niue. The impact of the weed can be best observed at the rubbish dump in Alofi South, where tall trees have been fully overgrown and smothered by the weed. The common name of the weed reflects its attractive fruit of a woody structure which is attractive for dried flower bouquets. The fruit contains several large seeds. The extent of its distribution places any eradication attempt in a similar category as S. aureus. It will require considerable support, which should be provided immediately to increase the chances for a successful eradication from Niue. African Tulip, Spathodea campanulata The distribution of this tree weed remains very restricted. It was only observed at a few sites in Alofi, one site in Hakupu, and at the Vaipapahi Research Station of the Department of Agriculture, Forestry and Fisheries. It is strongly recommended that these trees be cut and burnt, and a herbicide applied to the stumps to prevent regrowth. A perimeter of approx. 10 m should be inspected regularly for any shoots produced from roots. Wilco Liebregts 31 March 2001