Field evaluation of insect exclusion netting for the management of pests on cabbage (Brassica oleracea var. capitata) in the Solomon Islands Neave, S.M. AVRDC-THE WORLD VEGETABLE CENTER. 3 – 4 SIDT BLD, P.O BOX 147, HONIARA, SOLOMON ISLANDS
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Kelly, G. INDUSTRY & INVESTMENT, NSW. P.O BOX 62, DARETON, NSW 2717, AUSTRALIA
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Furlong, M.J. SCHOOL OF BIOLOGICAL SCIENCES, UNIVERSITY OF QUEENSLAND, ST LUCIA 4072, QUEENSLAND, AUSTRALIA.
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ABSTRACT This research evaluated the efficacy and financial feasibility of using exclusion row cover netting to exclude insect pests from cabbage crops as part of a management strategy. Two net materials, Evolution® Row Cover and MikroKlima® GrowCover were compared with the local practice (where insects are picked by hand or no control), at three locations in the Solomon Islands. The use of Evolution® Row Cover and MikroKlima® GrowCover resulted in 72% and 38% less pest damage compared to the local practice. There was little difference in size and weight of the heads harvested between treatments but there was an average increase of 40% in market price due to better quality heads grown under the MikroKlima® GrowCover. Although the Evolution® Row Cover provided the better protection, it was less durable and more easily damaged than the MikroKlima® GrowCover and needed regular repairs. Based on a predicted use of the MikroKlima® GrowCover for six crop cycles and the nature of the market at the time, the net present value for the Mikroklima® net treatment in Busarata was SBD 1,387.68 From the results of this study, there is a justification, both from production and financial perspectives, for using insect exclusion netting on high value crops in Solomon Islands, particularly if a cheaper source of durable netting can be found.
Keywords Plutella xylostella, floating row covers, economic evaluation, pest control
INTRODUCTION Vegetable growing in the Solomon Islands is predominantly small-scale production, either in home gardens or in small plots, and local, readily available inputs are used. Ball (=head) cabbage is a high value,
cash crop for many farmers. The main consumers of ball cabbage are expatriates and the food service sector, where they are mainly used in salads. The crop is in high demand but there are many production constraints and crop quality (and hence market prices) are poor; production is restricted to a small number of farmers in the highlands of Malaita province, where production is still profitable. Income generated from the sale of vegetables is important to rural households. In a baseline survey conducted in two provinces in 2008, 53% of the total income was through vegetable sales (Siliota et.al. 2008). Ball cabbage is a valuable income generator for farmers, as it is easily transportable, and has a relatively long shelf-life, compared to other vegetable crops. In addition, direct markets, such as hotels, restaurants and resorts, are showing increased interest in buying locally produced vegetable crops. However, these markets demand consistent and high quality supplies, but neither of these requirements is easily met. Consequently, significant quantities of cabbage are imported from Australia and New Zealand. In Solomon Islands, the vast majority of vegetable production is organic, with the few farmers that use pesticides mainly targeting Lepidopteran pests. It is, therefore, important to find alternative solutions to managing pest populations, without developing a reliance on the use of synthetic insecticides. Diamondback moth (Plutella xylostella) and other Brassica pests, including Cabbage cluster caterpillar (Crocidolomia pavonana) and common armyworm (Spodoptera litura) are major pests of ball cabbage (Brassica oleracea var. capitata) in the Solomon Islands. The population levels of species such as P. xylostella are significant enough to limit the production of ball cabbage to a few locations, mainly in the highlands. However, with the increase in production of watercress (Rorippa nasturtium-aquatica) in these areas, population levels of Brassica pests are becoming an increasing restricting factor for producers. Watercress is also an important food crop to the Solomon Islands, but is only grown for market in West Honiara and peri-urban areas of Auki. It is mainly grown in the streams in the mountains where stretches are dammed using logs or rocks. The production of watercress crops is limited by insect pests, mainly P. xylostella, that cause damage to the harvested leaves. One management strategy that is currently being tested is to grow the watercress on floating rafts, which are sunk periodically to drown the pests. In ball cabbage production, P.xylostella damages the developing leaves in early growth stages. Other insects such as C. pavonana and S. litura burrow into the young growing tips, damaging the developing head and making them unmarketable. The use of synthetic insecticides as a management strategy is neither appropriate or to be encouraged in the Solomon Islands. The farming practices presently utilize many natural resources such as mulch and compost. Pesticide supplies are limited and farmers have limited or no knowledge and skills about how to use them appropriately. The use
of exclusion row covers is an effective pest management practice that has been used to reduce caterpillar, whitefly, thrips and aphid numbers and crop damage in a variety of high value vegetable crops. In this research, the approach to managing pests in these Brassica crops is centred on methods that are appropriate for farmers in the Solomon Islands. Practical methods that utilized inexpensive, locally available materials that could be applied with little technical supervision were important. The purpose of the study was to determine the efficacy and cost effectiveness of an easy to use technology that could help farmers manage troublesome pests on a high value crop. To this end, the research focused on methods that could exclude the insect pests for periods long enough for crops to develop and set marketable heads. Exclusion treatments that included a floating row cover and an insect net that could be placed over the growing crop were chosen for comparison. The use of floating row covers to regulate crop growth is a well established technology which is practiced in many countries, particularly in temperate climates where it promotes the retention of heat, which enhances plant growth and earlier yields. Floating row covers (Reemay® and Vispore®) provided effective frost protection and extended the growing season of tomatoes and cucumbers in Oregon, USA (Nelson et al. 1985). In field studies, the row covers increased the transplant success rate and increased soil temperatures which helped stimulate fruiting and increased yields (Nelson et al. 1985). The use of floating row covers and pyriproxfen were shown to reduce fruit damage caused by silverleaf whitefly (Bemisia tabaci) on zucchini, resulting in an increased percentage of marketable fruit in Queensland (Qureshi et al. 2007). In that study, the floating row cover alone produced the highest marketable fruit for most of the sampling dates (Qureshi et al. 2007). Floating row covers combined with plastic mulch also helped control virus transmitting insect vectors on zucchini in Florida (Webb and Linda 1992). The row covers produced zucchini plants that were larger and more vigorous in size than uncovered plants which were infected with virus and stunted (Webb and Linda 1992). Virus disease incidence in cantaloupes was delayed due to row covers (Agribon-17) completely excluding insect vectors in Mexico (Orozco-Santos et al. 1995). The financial aspects of utilizing these techniques have also been investigated. The economic benefits to growers and consumers of using insect netting in greenhouse tomato production to exclude whitefly vectors causing tomato yellow leaf curl (TYLC) was proved (Taylor et al. 2001). This paper evaluates two types of row covers used in the management of cabbage (Brassica oleracea var. capitata) in the Solomon Islands.
MATERIALS AND METHODS The exclusion row covers and insect net, which are not locally available, were sourced from Australian suppliers and delivered to the Solomon Islands. Materials used to
make hoops to support the netting over the plots were sourced locally. Trials were conducted in three locations in the Solomon Islands - Busarata (Malaita), Henderson (Guadalcanal) and Tetere (Guadalcanal). Two of the locations (Henderson and Tetere) are in the lowlands, where ball cabbage can no longer be grown economically due to the constraint posed by insect pests, and a third location (Busarata) was in the highlands, where production exists. Two exclusion treatments (row covers) were compared with no exclusion (control) in field evaluations. The two exclusion treatments were; MikroKlima® GrowCover (Veggie net) (Supplier: Veggie Patch, Australia) is woven polyethylene netting of uniform weave, with a density of 35g/m2, 85% light penetration and 2 m width. Evolution® Row Cover [Supplier: Gundaroo Tillers, Australia; Manufacturer: Kimberly Clark (Australia & New Zealand)] is made from lightweight High Density Polyethylene (HDPE) fleece fabric, with a density of 20g/m2 and 2 m width.
Installation of exclusion treatments Immediately after seedling transplanting, the exclusion nets were placed over the cabbage plots. The nets were supported by 20 mm polypipe hoops (each 1.8 m long). Lengths (≈50cm) of 16 mm iron bars were pushed into each end of the polypipe, and were then pushed into the ground to secure the hoops. Hoops spaced 1 m apart were placed over the beds to support the nets. The nets were cut to length with an extra 1 m for tying each end. The nets were placed over the hoops and secured with ‘jumbo clips’. The ends of the net were tied and one edge was weighed down and buried. Exclusion net treatments that remained over the plots until harvest were periodically lifted on one side to weed, water, collect plant measurements and make observations. Trial Plot details All three trials had the same arrangement, using a latin square design with three replications. Plot sizes were approximately 1.5 m wide and 6 m long. The total size of each trial was also similar; 6.5 m wide (3 beds with a 1 m spacing between beds) and 20 m long (6 m plot lengths with a 1 m spacing between plots). Beds were hand cultivated and prepared with compost and manure approximately two weeks prior to transplanting cabbage seedlings which had been raised on farm nurseries.
Trial locations Location 1: Busarata The trial at Busarata, Malaita was established on 22nd April 2010. Busarata is located in the highlands 800 m above sea level and consists mainly of steep land that is loosely terraced. The soils are sandy loam (no soil analysis completed) with pH 7. In this location, carrots and onions had been grown previously on the site. Twenty seedlings were transplanted into each bed, in two rows (30 cm apart), 60cm spacing, after the nets had been put in place. Harvest was conducted on 9th August 2010.
Location 2: Henderson The trial at Henderson, Guadalcanal was established on the 6th May 2010. Henderson is located 11 km east of Honiara, on the edge of the Guadalcanal plains. The land is low lying and periodically flooded by storm water runoff from the airport. The soils are clay loams and are quite low in nitrates (14 nitrate-N/ha) and have a pH of 6.5. In this location, rock melon had been previously grown on the site. Twenty seedlings were transplanted into each bed, in two rows (30 cm apart), 60 cm spacing, before the nets were placed over the hoops. Harvest was conducted on 19th July 2010.
was similar (in terms of plant growth). There was a significant difference in the number of leaves produced between sites at growth stage 1 (F2,15=12.21, p
