Agnote 693 No. I31 September 1996 Agdex No: 683 ISSN No: 0157-8243 Dimethoate as a Post Harvest Treatment J. Alcock, Chemicals Co-ordinator, Darwin A post-harvest dimethoate dip or spray of mangoes for fruit fly control is a quarantine requirement for certain markets. USE OF THE DIP When dipping, the fruit should be fully immersed for 1 minute in a solution containing 400 mg per litre of dimethoate. This is achieved by mixing 1 mL per litre of a commercial product, which contains 400 grams per litre of the active chemical dimethoate with clean water of pH 7 or less. There must be enough dip mixture in a suitable sized tank to allow the fruit to be fully immersed. Produce should be placed into an open weave basket which is then placed into the dip A top is necessary to ensure that fruit is fully immersed and does not float. Ensure that the fruit is immersed for one minute only before removing from the tank. The produce is placed on to a drain tray before packing. Make sure this is the last treatment before packing. It is important to use fresh dimethoate and to monitor the dip concentration regularly. The initial concentration should be checked, then re-checked on day five, or sooner if it becomes severely contaminated with sap or dirt. Fruit sap, dirt, alkaline de-sapping chemicals and other waste material will contaminate the dip, making it less effective and more likely to produce post harvest rots unless changed. LOCATION OF THE DIP Locate dipping tanks as far as possible from water courses. The dipping area should be concrete floored with a bund wall around it to contain spillage and runoff. A blind sump (with no outlet) within the bunded area makes spills easier to recover. Position the tank in a well ventilated location. Dimethoate dipping is best done away from the shed because the fumes may cause nausea. If the dipping is done in the shed an effective exhaust system is necessary. USE OF A FLOOD SPRAY Alternatively, the fruit can be flood sprayed with a mixture containing 400 mg per litre of dimethoate in a high volume application of at least 16 litres per minute for each square metre of the area being flood sprayed. The fruit must remain under the flood for at least 10 seconds after which fruit must remain wet for an additional 50 seconds. The solution can be recirculated. NOTE: Dimethoate solutions should not be used if they are more than 18 months past the date of manufacture on the label. To avoid waste, purchase only small volumes. Products older than twelve months can be checked by providing Chemistry Branch with a sample. DISPOSAL OF SPENT DIMETHOATE For disposal of spent dimethoate, add 3 kg of either slaked, hydrated or quick lime per 1,000 litres of dip solution in a separate vessel to the dipping tank. Leave that mix for two hours to neutralise the chemical component. The chemical reaction may generate strong smelling gases so make sure this procedure is conducted outside and away from any place where the odour could cause a nuisance. The inactivated mix can then be poured into a trench, or sprayed on grass. Make sure the neutralised dip is disposed of at least 50 metres away from any streams, drains, channels, wells, boreholes or water courses. NOTE: When using lime or handling alkaline solutions wear goggles and industrial quality synthetic gloves. Please visit us on our website at www.primaryindustry.nt.gov.au While all care has been taken to ensure that information contained in this Agnote is true and correct at the time of publication, the Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. No serious, business or investment decisions should be made in reliance on this information without obtaining independent/or professional advice in relation to your particular situation.