SFF Project Summary
Management and control of onion thrips in export onions
Final Report: Final Report [
PDF 54K]
Background
From 1997 the NZ onion industry had serious problems in controlling onion thrips in the field and this lead to loss of skins, shrinkage of bulbs and development of secondary moulds on onions during shipment to northern hemisphere markets. These were the main markets for the 160,000 tonne NZ onion export industry. This loss of quality resulted in serious damage to the reputation of NZ onions, and potential to lose part of those markets, as the premium quality higher priced outlets.
A TBG funded project clearly showed there was resistance to a group of commonly used insecticides and a management strategy was implemented over the two years from 1998 to 1990 to overcome this resistance. This was successful in restoring good control of onion thrips during the growing period in the field but indicated there were further problems developing during harvest and handling, and extended to include the conditions during shipment.
This SFF project was initiated to build on these previous developments with control of onion thrips in the field, and was focused on identifying the best handling practices to minimise the potential for thrips to damage onions after harvest, leading to acceptable outturns in off-shore markets. It did not include any aspects of insecticide use to control thrips in the field, but did include 2 new fumigation products.
The project was developed by the NZ Onion Exporters Assn. in consultation with a wide range of the onion industry from several planing meetings in winter 2000, and implemented with the support of the Sustainable Farming Fund in November 2000.
The project utilised the expertise of the research organisations which had assisted with the first part under TBG funding, as Crop & Food Research Ltd and Hort Research.
But it also used the commercial expertise of fumigation suppliers and applicators for the disinfestation tests, and the expertise of some export companies for quality assessments, and in tracking onions through to the final outturns.
Main outcomes
The main points to come from the project for industry use were believed to be:
- the ability of thrips to breed and increase on onions varies with different lines or strains and may lead to selecting “ resistant “lines of methods of production,
- numbers of thrips can increase rapidly up to about 30 C, but at higher temperatures mortality increase so there is no survival beyond 7 days at over 37 C,
- best topping practices were shown to be those that left a longer top length, or lifted and topped at harvest to minimise thrips entry onto bulbs,
- complete skin cover on the bulbs reduced thrips access to bulbs, and split skins allowed adults to survive on bulbs and increased thrips numbers on bulbs in storage,
- crops with thrips numbers exceeding the thresholds had greater thrips numbers buildup in storage, thrips clearly increased in numbers during on-shore storage,
- black mould risk on onions was related to number of years onions had been grown on the field, as well as to conditions which suit black mould development,
- yellow sticky traps in the bins in storage were only a moderately useful indicator of thrips numbers in a line, but were readily contaminated by other insects to make use difficult.
- Fumigation with Carbon dioxide at elevated levels for 3 days killed adult thrips, but not eggs,
- Phosphine gas as Ecofume was able to kill adults and eggs, but may not be acceptable due to residues in onions, and a market preference for avoiding post harvest chemical use.
- offshore assessment of bulb quality and thrips numbers was only partly completed due to loss of lines in the export chain, and was the only part of the whole project considered to be incomplete as planned.
