South Australian Lettuce Aphid Update

Since the last Lettuce Aphid update some months ago, much has happened not the least of which, is the incursion into South Australia of this pest.  Currant lettuce aphid (CLA -Nasonovia ribis-nigri) was confirmed on a lettuce growing property in the Virginia region in early May.  Information provided by the grower confirmed that CLA was present in both hydroponic and field grown production sites.  The grower only produces loose leaf lettuce and does not use resistant varieties nor Confidor treated seedlings.

Extensive surveys were subsequently undertaken to determine the extent of the infestation.  The surveys revealed that Currant Lettuce Aphid was also confirmed in Lettuce samples collected from a property located in Uraidla.

An emergency meeting was held by PIRSA Plant Health and representatives from the SA Lettuce growing community at Virginia Horticulture Centre and it was agreed for the removal of all import restrictions put in place against Currant Lettuce Aphid and the movement of its hosts (as detailed in the Plant Quarantine Standard, South Australia 2006). 

A SARDI Entomologist was present at the meeting and indicated that it was likely that this Spring there will be an increase in the movement of CLA into areas where this pest has not been detected previously.  Management of CLA, the use of resistant varieties and the effects that this pest may have on the retail trade was also discussed. 
Safe management options are ready to use and monitoring techniques developed by State Departments of Agriculture are in place to give early warning of the pest's arrival on your property and provide the best advice for managing the problems and minimising the damage this pest can cause.

Solutions Currently Available
  1. Resistant varieties - Some seed companies have utilised an aphid resistance gene in some of their lettuce varieties. Lettuce aphid does not feed or reproduce and immature stages do not reach adulthood on resistant plants. Other seed companies are now also using this gene and have a range of fancy lettuce ready for commercialisation, but head lettuce varieties are not yet available.
  2. Source control - Care should be taken that lettuce aphid is not introduced via transplants or movement of other plant material.  Ensure that seedlings are Confidor dipped prior to planting.
  3. Monitoring - Crops need to be closely inspected. In seedlings and pre-hearted lettuce, attention needs to be paid to the innermost leaves and in folds or crinkles in the leaf. Once the lettuce has hearted some destructive sampling is needed. Since lettuce aphid may occur non-uniformly across paddocks, a number of widely dispersed sites need to be sampled. Weed hosts should be sampled, including Hawksbeard and wild lettuce if nearby.
  4. Beneficial insects - Aphids are eaten by a range of beneficial insects which are likely to be more efficient at reaching and killing them than insecticides, particularly in hearted lettuce. However the use of broadspectrum insecticides is likely to kill many beneficials.
  5. ‘Soft’ foliar insecticides – Pirimicarb (Pirimor®) is a ‘soft’ aphicide registered for use on aphids in lettuce in Australia. Although resistance has been reported to pirimicarb in Europe, tests in NZ show that their lettuce aphid is not resistant. There are some newer potentially ‘softer’ chemistry that is not currently available that may get permits or registration.
  6. Broadspectrum insecticides. Dimethoate, maldison, methidathion (e.g. Supracide®), and pyrethrins are the other registered aphicides for lettuce in Australia. In Europe resistance to cypermethrin, dimethoate, and endosulfan has been recorded. Broadspectrum insecticides are undesirable in an IPM system as they kill most, if not all, beneficial insects.
  7. Seedling drenches. An emergency permit has been granted for imidacloprid (Confidor®) as a seedling drench in lettuce. Seedling drenches have been proven to control lettuce aphid for the life of the crop in New Zealand. Imidacloprid seedling drench is not fully compatible with IPM programs. Overuse of imidacloprid for lettuce aphid control raises concerns with resistance developing. A resistance management strategy is being developed and should be followed when introduced.
  8. Sanitation. Control surrounding weeds. Any infested lettuce, including recalled product, should be buried as soon as possible.
  9. Post harvest washing. Washing of head lettuce will not disinfest. Loose leaf lettuce washing processes with fine water filtration systems can reduce numbers of aphids present in packed lettuce.
Growers with a strong IPM strategy and good populations of beneficial insects are in a better
situation to manage lettuce aphid populations, particularly when they first arrive in a district. 

To this end, Paul Horne of IPM Technologies will be in the Northern Adelaide Plains to present outcomes of IPM trials with interstate growers on Monday 16th of October and also will be available to visit a few farms in the region. 

For more information contact Melissa Fraser, SA Vegetable Industry Development Officer on (08) 8303 6714 or Stacee Brouwers, Agronomy Officer with the Virginia Horticulture Centre on  0402 313 179
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