Question 1 from Bev: I have just planted some cabbage plants, and what strategy can I adopt to prevent white butterfly laying their eggs? I am on the coast of the Coromandel Peninsula
Many thanks, / Question 2 from Robin Sage: I live in the back of Taihape where I have a large vegetable garden. The
Brassicas are being eaten alive by the white butterfly. I have been
advised against using derris dust because of its harmful effects and
would be grateful if you could recommend a safe insecticide. I would
love to receive your newsletter too.
Low hazard pest controls:
light flour dusting
diatomaceous earth (available from pool supply shop)
encourage predators - wasps, assassin bugs, laceworms, toads, birds
Bacillus thuringensis Bt
This is a bacterium that parasitises the caterpillar and causes fatal vomiting. Trade names are Dipel and Thuricide.
Use of aromatic herbs:
Attractants to lure pests away from crops - plant hyssop near cabbage (an excellent lurer, entices away cabbage white butterfly and stops infestations of caterpillar, especially the cabbage white butterfly), also coriander and wormwood.
1. Soak 75g chopped garlic bulbs in 2tsp mineral oil for 24 hours. Add 1 pint water mixed with 7g soft soap. Stir well and strain in non-metallic container and store. To use: dilute 1 part of mixture to 20 parts water.
2. Boil 10 cloves garlic, 4-5 very hot chillies, 2-3 onions for 5-10 mins. Stand overnight. Add liquid soap or milk. Store in glass bottle. To use: 1 small cup mixture to 7 litres water.
Grind dry flowers or extract with kerosene. Remains toxic for 12 hours. Non toxic to mammals, but this will kill bees, ladybirds and other beneficial predators. Spray in evening when bees etc, are less active.
50g common salt to 3.7 litres water.
Use soft soap (made with potassium carbonate and not caustic soda) Dissolve 50g in 4.5 litres hot water. Apply when cool.
Bordeaux mixture (copper sulphate spray):
100g copper sulphate dissolved in 1 litre of hot water. Add mixture to 150g hydrated lime in 1 litre water. Stir well. To use: Dilute with 10 litres water. For spring use, dilute further 1 part mixture to 10 parts water. Use within 24 hours of making up. Use at 2-3 weekly intervals.
Encourage beneficial insects:
German wasp (vespula germanica). Common wasp.
Hoverflies, syrphid - encourage with pollen and nectar flowers, especially blue, yellow or white colours; also use phacelia, daisies, yarrow, white cosmos and French marigold.