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Wednesday, July 7, 2010

Murder in the Garden: Organic Pest Control Remedies

There is no doubt that when vegetables are at their peak performance, little critters find them irresistible and begin  chomping away at our beloved plants we have weaned from seed.  Those of us who are gardening organically have two options — 1. grab those suckers and stomp them with your boot. 2. Find a natural spray that will do the dirty work for you.
 For some who are trying a hand at growing their own food all have found different challenges along the way.  Luckily, thanks to the information age, there is knowledge available from those who are more than willing to share the wealth of knowledge.  Annette McFarlane, an experienced gardener and author of Organic Vegetable Gardening has been kind enough to share some of her secrets to organic gardening.  To help rid the garden of non-beneficial insects (otherwise known as pests), here are a few concoctions that can help remedy gardening problems we find along the way.   
Tree Pastes
Tree pastes are used as an aid to tree vigour and for pest and disease control. Biodynamic gardeners routinely use tree pastes during winter. The original formula proposed by biodynamics founder, Rudolf Steiner, was composed of:
 4 parts cow manure (naturally aged, not processed products)
2 parts diatomaceous earth* or silica sand
3 parts fine clay* or bentonite*
 My own experiments centre on insecticide grade diatomaceous earth as the primary ingredient. I use pastes to prevent borer attack and control scale infestation on roses and citrus. It should be noted that insecticide grade diatomaceous earth is not the same as the heat treated and highly dangerous diatomaceous earth used in swimming pool filters.   
 *Insecticide grade diatomaceous earth is available in domestic quantities from Green Harvest.  Bentonite can be purchased from most produce stores, but is usually only available in large bags. Potter’s clay is available in small quantities from discount stores and craft suppliers.   
 Black Spot Spray/Bicarb Soda Spray
1 tablespoon of bicarbonate soda
4.5 litres of water
1 tablespoon of homemade Oil Spray concentrate (see below) or commercial oil spray (vegetable oil based)
Spray weekly as a preventative treatment to minimise black spot and mildew.  Improve air circulation around plants.  Avoid wetting the foliage and thin out overcrowded growth. Remove any leaves affected by black spot as soon as they are sighted.
 Casuarina Tea
Casuarina trees contain high levels of silica. Biodynamic gardeners make a spray made from casuarina foliage for use against fungal diseases like anthracnose and other mildews.
Simmer 60gm dried Casuarina needles in one litre of water for 20 minutes using a stainless steel container.
Strain and dilute 1 part concentrate to 40 parts water.
Spray in the air around trees early in the morning.
 Garlic Spray
Three large cloves of crushed garlic
1 tablespoon of vegetable oil
One teaspoon of liquid soap
One litre of water
Combine the garlic and vegetable oil and leave to soak overnight. Strain and add to the litre of water along with the liquid soap. Spray regularly. Garlic in known for its antifungal and antibacterial properties, but it is its insect repellent qualities that most gardeners admire.
 Powdery Mildew Spray/Milk Spray
Powdery mildew appears as grey or white powdery spots on the new foliage.  It causes puckering of the foliage and in severe infestations, a burnt appearance and leaf fall.   This disease occurs most frequently when night temperatures drop and relative humidity remains high.  Avoid the over-use of high nitrogen fertilisers as these can tend to make leave growth that is soft and more susceptible to disease.
1 part of milk
9 parts of water
Spray regularly over the leaves, paying particular attention to soft new growth
 Homemade Oil Spray
Mix 500ml of vegetable oil
½ cup of Sunlight dish washing liquid or other pure liquid soap
Blend thoroughly and seal in a clean, clearly labelled jar. Store in a cool area for later use.
Dilute one tablespoon of the concentrate into one litre of water before spraying.
Oil based mixtures can be used to suffocate mites, scale and other soft bodied insects. They help to repel leaf miner moths and some gardeners even find them effective against grasshoppers. Avoid using on plants with hairy leaves and during very hot weather.  
Molasses Spray
Dissolve one tablespoon of molasses into a litre of warm water.
Add one teaspoon of Sunlight dish washing liquid or other pure liquid soap
 Spray regularly over the leaves of all plants attacked by caterpillars and other chewing pests. Caterpillars would rather starve than eat leaves sprayed with this mixture. It has also been used with success by some gardeners as a possum repellent and for the treatment of soil affected by root knot nematodes by doubling the concentration of molasses.   
 Chili Spray
Small hot chillies (40-50)
2 litres of water
5 grams of pure soap flakes dissolved in hot water or a few drops of liquid soap
Puree the chillies and one litre of water together in a blender. Strain the mixture through a fine sieve and add the soap and the other litre of water. Spray this mixture undiluted on to plants.
This spray is a favourite with warm climate gardeners who have chillies in abundance almost year round. If you do not have a chili bush you can substitute chili powder or paste. Chili spray is particularly effective against ants, aphids and other soft-bodied insects.   
 Warning - This mixture can look attractive to children, so be sure to label correctly and store out of their reach. Wear gloves when spraying and ensure that the mixture does not come in contact with your skin or eyes.   
 (This text contains an edited extract from Annette McFarlane’s book, Organic Vegetable Gardening, published by ABC Books). 


  1. Another green pest control method that works well is to put ladybugs in your garden. Ladybugs eat aphids so they will naturally solve the problem.