ACCE$$ TO A$IA ASIAN VEGETABLES NEWSLETTER Issue No. 12, April 1997 (English Edition)

This is the second issue of the bimonthly Asian vegetables newsletter for 1997. In this issue, we will present some research information on management tactics for diamondback moth. The usual information of a particular Asian vegetable for supermarket requirements will be held back.

INSECTICIDE RESISTANCE IN DIAMONDBACK MOTH:
A CHALLENGE FOR GROWERS OF ASIAN VEGETABLES
(Nancy Endersby and Peter Ridland, Tel. (03) 9210 9222)

Growers of cruciferous vegetables throughout Australia have faced massive problems in recent years due to insecticide resistance in diamondback moth (DBM). Insecticide failures and high levels of crop damage led to thousands of unmarketable vegetables being ploughed under. Caterpillars of DBM, Plutella xylostella, only feed on crucifers and are a particular problem on Chinese cabbage, Chinese broccoli, Chinese flowering cabbage, Chinese chard, Shanghai Chinese chard, Baby Chinese chard and mustard green. Other vegetables include brussels sprouts, cabbage, cauliflower and broccoli.

Worldwide, DBM is the most destructive pest of crucifers because it has become resistant to many types of insecticide. In some countries, particularly in parts of Asia, it has rapidly developed resistance to all insecticide groups including the bacterial insecticide Bacillus thuringiensis and new generation chemicals such as insect growth regulators. In some areas there are no insecticides which will control the pest. Insecticide resistance in diamondback moth in Australia was first recorded in Queensland about ten years ago.

What is Bt?

Bt is short for Bacillus thuringiensis, a bacteria which is used
as a biological insecticide. It is only active against caterpillars and is very
valuable in managing DBM. Bt products include DiPel Forté, Delfin,
Novosol Biological Insecticide, Biobit, and Thuricide.

How Bt works:

Bt insecticides contain living spores and toxic crystalsThe caterpillar eats the Bt and the crystals pierce its gutSpores move into the caterpillar's body and multiplyCaterpillar dies of blood poisoning in 1-3 days. Remember with Bt, caterpillars take 2-3 days to die but they don't feed after eating Bt.

MANAGEMENT STRATEGIES FOR DIAMONDBACK MOTH

There is no longer an easy answer to how to control DBM. A number of strategies must be used at the same time. This is called an Integrated Pest Management (IPM) approach. An important part of this approach is checking the crop for pests. In the cooler months of the year, spray applications can be saved if low number of caterpillars are observed.

Clean transplants are essential

• Look for eggs, caterpillars and feeding damage

Begin checking your crop early

• Walk through and check your crop at least once a week
• Keep track of Plutella numbers
• Check whether previous sprays have been effective
• If you can't do it, send somebody else
• For successful management you must know what is going on in your crop

Keep records

• Record spray, date, rate, weather & success of application
• This is valuable for future management

Spray at the right time

• Are you getting the best crop coverage you can?
• Calibrate your spray rig and replace worn spray nozzles or calibrate your backpack sprays
• Get the spray under the leaf where Plutella caterpillars feed
• Spraying late afternoon or at dusk reduces spray evaporation and breakdown
• Use wetting agents at label rates

Spray the ends of your beds thoroughly

• Pest pressure is heaviest at crop edges
• Don't let the ends of the beds become breeding grounds

Destroy crop waste

• Plough under crop waste after harvest
• Destroy cruciferous weeds such as wild radish and wild mustard

Use Bt as the foundation of your program

• Use label rates