Disease control in the garden with Annette McFarlane - video transcript

This page is a transcript of the Disease control in the garden with Annette McFarlane video on Brisbane City Council's YouTube channel. The video is 12 minutes and 22 seconds long.


>> ANNETTE: Welcome to winter in Queensland. It's a glorious time of year here on the coast. Lot of things are flowering and we have lovely cool conditions for growing. We can grow lots of things that we can't grow at other times - violas and pansies, ots of other annuals. People are planting bulbs that will be up in the springtime - towards the end of August and into very early September.

It's also a time of year when our plants suffer diseases. There are things we can do to control diseases and there are a lot of things we can do to prevent them. It's important to remember that the organisms that cause disease (fungi and bacteria) are in the air; in the soil and in water.  They are around all the time, just waiting for the opportunity to take off. Winter sometimes provides that opportunity because it's a time of year when we often have heavy dew in the morning and cooler temperatures overnight. That combination is perfect for some diseases, particularly powdery mildew.

It is also a time when plants are in a more dormant phase. Trees, shrubs and fruit trees are slower growing because the soil nutrients aren't as readily available. We find our citrus; pawpaw and ixora plants are slower growing because they can't access the nutrients as readily from the soil.

This combination provides the ideal storm. Bacteria and fungi are waiting for their opportunity. Conditions are right with moisture in the air in the early mornings; cold temperatures overnight and susceptible plants.

It's really important to make sure your plants are getting the balanced nutrition that they need. While gardeners in really cold climates tend not to fertilize through winter time, it's quite important for us to apply trace elements; to put rock dust and other minerals on to the soil. We need to cut back on the amount of nitrogen, but use potash in the soil and silica on plants help prevent disease outbreaks.

If you do have a disease outbreak, there are plenty of things that you can use you might have on hand – milk, bicarbonate of soda or even leaves from some of the trees growing in your garden. Let's go take a look.

Vegetables that don't get enough sun in the wintertime really suffer from problems like powdery mildew and other leaf spot diseases. A simple spray of bicarbonate of soda can be a real boost to them. Use it preventatively. If you know the garden is going to suffer, put it on in advance. You can re-spray every week if you need to, or every time you think it's necessary.

For the vegetable garden, I mix one tablespoon of bicarbonate of soda with one teaspoon of soap in a 2l spray. That is because some leafy vegetables are very sensitive to oil that we might otherwise put into the spray if we were using it to spray roses (See spray recipes below).

If you grow roses or fruit trees you might have heard of Bordeaux spray - in fact you might have even used it in the garden. You can make your own. It is traditional spray used for fungal and bacterial diseases that has been used by gardeners for hundreds of years. It combines hydrated lime (also known as slaked lime or builder’s lime) and copper sulfate. It is great for diseases like black spot on mangoes; diseases on pawpaw, roses, tomatoes as well as peach leaf curl and a range of other diseases. Generally, we spray just once in the wintertime – it is not a spray we usually apply in the warm weather.

Take a few precautions when you making up Bordeaux. Use hydrated lime not garden lime. Remember that you cannot use the hydrated lime for general use in the garden. It is too strong. If you put it on your lawn (some gardeners I know have made that mistake), you'll find your worms will be packing up and heading to the next door neighbours. 

You need to use Bordeaux mix immediately, so make it up fresh and use it straight away. I soak and prepare the ingredients the night before. Spray over the trees during winter and once during the growing season on our tomatoes which in Queensland is generally also in wintertime.  To make up two litres of Bordeaux mixture will need 20g of hydrated and 20g of copper sulfate mixed in two litres of water (see recipe summary below).

I have dissolved my 20g of hydrated line in one litre of water and left that to dissolve overnight. Here is the 20g of copper sulfate dissolved in 1litre of water. I've used the traditional method to putting it in a stocking and leaving it to soaked overnight. It's important to make sure you mix the hydrated line into the copper sulphate and not the other way.

Wear gloves, eye protection and protect your clothing. Mix together slowly for a traditional lime and copper sulphate mix or Bordeaux that is ready to use. Put it into a sprayer using a funnel and use within a 24-hour period.

Bordeaux is a great treatment for your mangoes in the cooler months of the year to help control black spot disease and anthracnose (that terrible disease that hits your plants before flowering or at flowering when we have rain in winter). If you grow a bay tree that gets disease problems use Bordeaux during the winter time. It is a great treatment and last quite a long time. It is not easily washed off by watering or rain.

On lemons that have finished fruiting for the year, apply Bordeaux as protection against disease for the coming season. Normally we treat after fruit harvest. Spray all over the leaves - undersides, top sides and all down the trunk and branches.

Concentrate on the new foliage that's coming away from the centre of your pawpaw and also spray the young fruit. Remember this is a preventative spray, so the leaves that have already been affected will not be helped all that much – those spots will not go away. Bordeaux will protect new foliage at the top of the crown. Don’t forget to spray the green fruit. They probably will no mature until about September in Brisbane. You want to protect them from ripe fruit diseases that they might otherwise occur through the cooler months.

A related mix some gardeners might find easier to make up is a Burgundy mix. It combines copper sulfate and washing soda. It is also very useful against fungal diseases and mildew diseases (see recipe below).

Biodynamic growers use Casuarina leaves for the silica they contain. Silica is really important in plants and you can make your own spray need. You need about 60g of dried leaves (dry for 5-7 days). Boil them in 1litre of water for 20 minutes (see recipe summary below). You will see colour coming out into the water.  Dilute two tablespoons of the cooled mix in one litre of water. Spray on plants to increase the silica level and disease resistance.

If you only have a few pots, try a milk spray. Mix nine parts water to one-part full cream milk. Spray over the plants as often as you like. It’s great against mildew disease and you can use it in winter and summer (see recipe summary below).

So, there you have it. Remember diseases around in the air, in the soil and in water all the time. They are just waiting for conditions to change - for temperatures to drop or sometimes increase; for moisture to be around to enable them to reproduce; for susceptible plants.

Keep your plants healthy. Choose the most disease resistant varieties. Use compost and trace elements. Don't overuse nitrogen fertilizer.  That will make plants softer and more susceptible to disease. When diseases occur, have some simple preventative measures on hand - Bordeaux and Burgundy mix in the winter; bicarbonate of soda or a milk spray.  If plant is subject to disease over and over again, think about whether it is suitable for the climate.

Next time I'll be back telling you about tree pastes for preventing borers and generally keeping trees healthy in the garden.

Annette McFarlane is an author; garden columnist; magazine contributor; radio presenter and former senior horticultural teacher. She presents free sustainability workshops in Brisbane City Council libraries. 


Recipe summary

Bicarbonate of soda spray - vegetables

1 tablespoon bicarbonate of soda
1 teaspoon soap
2 litres water

Use for leaf diseases on vegetables. Changes pH of leaf surface.

Bicarbonate of soda spray - roses, shrubs, perennials

1 tablespoon bicarbonate of soda
1 tablespoon oil
2 litres water

Use for black spot diseases on roses, shrubs, perennials. Changes pH of leaf surface.

Bordeaux mix

20 grams hydrated lime (dissolve in 1 litre cold water)
20g copper sulphate (dissolve in 1 litre cold water)

Add the lime mix into the copper and spray immediately. Agitate the sprayer regularly as the lime tends to settle out.

Burgundy mix

3-5 grmas washing soda (dissolved in 1 litre cold water)
20g copper sulphate (dissolve in 1 litre cold water)

Add the washing soda into the copper mix. Spray on dormant/deciduous plants - peaches, apples etc).

Casuarina spray

60 grams dried casuarina leaves
1 litre water

Boil leaves for 20 minutes. Cool, then dilute 2 tablespoons per litre water.

Milk spray

1 part full cream milk
9 parts of water

Combine and spray immediately.


Last updated: 29 April 2021
Topics: library