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Natural pest & disease control in a winter garden

Winter in Perth is mild by world standards - we can enjoy some lovely sunny days in the garden. Winter vegies grow nicely often without much input; depending when you plant, you can be enjoying harvested crops & replanting regularly.  In cold snaps, cooler weather does mean slower growth, and remember to consider whether frost protection is needed.

Besides old Jack Frost, there are garden pests over winter which you need to be on the lookout for. Snails and Caterpillars are about and your young seedlings are particularly vulnerable.

Spending time in your garden often and observation is the greatest defence – act early and you can avoid many problems. Here are some safe ways to keep the upper hand:-

Make your own snail traps using beer! Use a saucer or an old plastic container (eg. Margarine) dug into the soil slightly so snails have access. Use an upturned pot or similar as a cover, angled to allow entry. This serves to protect the beer from rain.

A night assault with a torch and gumboots is a fast way to get numbers down. Doing this nightly for 3 or 4 nights will make a dramatic impact on population. A bucket half full of salty water (to drop them in) will also kill snails.

If you use pellets, use an iron based compound like “Multiguard” which are non-poisonous to soil life and far less toxic to pets and wild life.  GLSC also carries "Protect-Us" pellets - also iron based, and Certified Organic.


Removal by hand is time consuming but effective. The little green caterpillars are usually found under leaves, close to the veins. They can be tiny and hard to see. Often their droppings (“frass”) is the best way to find them. “Dipel” is a product containing natural bacteria that will kill caterpillars but is safe for us.

July/August is when the black fuzzy caterpillars appear. These are the larvae of a native moth. Often they are thought to be spitfires and killed on sight. (Spitfires eat the young growth of eucalypts, not vegies, and cluster together in a large clump.) Unless the fuzzys are really decimating your crops, try to be a little more accommodating – they are only around for a short time and won’t reappear until next winter.

With winter rains and cooler nights causing heavy dew, gardeners can rejoice that they are not spending time (or money!) watering. This is great, but unfortunately the extra moisture around can promote fungal and bacterial diseases in your garden.

If you do need to give your garden supplementary hand watering over winter, do so in the morning to allow leaves to dry during the day. Ensure adequate air circulation around plants. Weed growth and crowded plantings cause a damp microclimate around stems and lower branches which is ideal for a range of diseases. (Not to mention providing a great hiding place for snails!)

I have read that removing one weed before it goes to seed will prevent at least nine weeds next year. Whether or not that’s accurate – it’s worth remembering! Pulling weeds is easier when the soil is slightly dry. It’s not exciting, but worth doing for the overall health and appearance of your garden.

Hygiene is important – any diseased plant material should be pruned and disposed of in the bin, rather than composting. Any affected leaf matter should not be allowed to collect under the plant, as disease spores can easily reinfect lower branches.

Many cold and moisture related problems will simply disappear once the weather warms, but if you have an issue then preventative action is always better than trying to restore a very sick plant.

Here are some simple sprays you can make at home which are inexpensive and effective! (Remember all of these are surface sprays and will need to be reapplied after rain.)

Garlic Spray

(Excellent for preventing fungal disease, and is effective against snails, slugs and aphids.)

Blend 250gm crushed garlic with 100mL liquid paraffin (available from pharmacies and many supermarkets in the medicine aisle). Leave overnight then strain through a fine mesh or cloth. Add to 1.5L of soapy water. (Soapy water is made from using a vegetable soap, rubbing with your hands until the water looks milky. Pure soap flakes can also be used; 1 teaspoon per 500mL is adequate.) Stir or shake well prior to use. This recipe should keep in a sealed container for several weeks.

Sodium Bi-carb spray (for blackspot and mildew)

Add 1teaspoon of bicarb, ½ teaspoon of vegetable oil, and 1 drop of dishwashing detergent to 1L of water. Stir well and use immediately.

Milk Spray (for blackspot and mildew)

Mix one part cows milk to 10 parts water, shake well and use immediately.

And don’t forget - healthy soil means healthy plants which are less susceptible to pests & diseases.

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