Yesterday on walking around my garden and found what I thought was a fungal disease on my cucumber plants. On looking again this morning, I found a little on some of my tomato plants too. On looking into this problem, I found that the issue is likely to be powdery mildew which can be a common problem.

Powdery mildew is caused by a few related fungi species that cause similar symptoms in a few susceptible species. It is common and can cause damage to infected plants, and is worse in summer and autumn. Spores are spread by wind and rain-when these spores land on susceptible plants, they cause an infection. Severe infections can cause younger shoots to become weaker which can distort leaves and ruin flowers. As you will see from some of the photos, the fungus grows really well on infected leaves.

Ideal conditions

This does depend on the specific species of fungus. Those that infect apples, hydrangeas and calendulas prefer warm but humid conditions, while those species that infect plants like beans, cucurbits, silver beet, roses and strawberries favour warm, dry weather where the morning dew is sufficient for enabling spore germination. Crowded conditions are also a factor when air circulation is an issue.

Susceptible plants

Fruit and vegetable plants that are prone to infection include:

• Apples
• Cucurbits
• Grapes
• Pawpaws
• Silver beets
• Strawberries
• Tomatoes

Ornamental plants prone to infection include:

• Calendula
• Crepe Myrtle
• Daphne
• Hydrangea
• Rose

Symptoms

The first sign of any symptoms is the appearance of powdery spots on both sides of the leaves. These spots grow and join up until the whole leaf is covered. The powdery spots can a;so develop on the stems, shoots, buds, flowers and fruits depending on fungus and host species.

Young leaves can turn yellow and begin to curl, flowers can become distorted and apple fruits may have skin that becomes russeted.

Prevention

The best way of dealing with any pest or disease problem is to prevent it happening in the first place. In this case there are several things you can do, including:

• Don’t overcrowd your plants
• Prune plants where possible to improve air flow
• When watering, don’t get the leaves wet where possible
• Apparently, spraying leaves with seaweed solution can possibly help prevent or reduce infection, but I can’t comment on this as I haven’t tried it!
• Grow resistant cultivars

Control

• Prune off any infected plant parts and dispose of them in your normal general waste bin. Clean any pruning instruments with a mild bleach solution once finished.
• Research has been done on a 10% milk solution (1 part milk to 9 parts water) that is apparently effective at controlling the infection, especially in the early stages. Again I haven’t tried this so can’t comment of how well it does.
• There are chemical controls, but as there are likely to be people reading from all over the world and the chemicals used to control such things can vary in how legal they are, I wont suggest them here. Also, I don’t want to start using them myself for various reasons. All I will say is do some good research on the correct fungicide to use and follow the instruction provided on the product label.

How have I dealt with powdery mildew in my garden?

On looking at the infected cucumber plants, they were riddled with powdery mildew. I decided that i was best to remove the plants completely to try and prevent any more major damage. This means I will have less cucumbers, but I really don’t want to lose a lot more! I also pruned all the infected leaves off my tomato plants to hopefully prevent more damage.

While I was away, the conditions were perfect for infecting cucurbits-warm (sometimes I’d call it hot) and dry. As I wasn’t around to try and stop the problem. It decided it was time for a party! It doesn’t always help that when we are at home, we have doors and windows open to take advantage of the breezes that flow through our home to the patio area. When these doors aren’t open, the patio area is quite protected with little wind-another issue that didn’t help!

Going forward, I’ll have to try and keep my plants further apart, be more vigilant to get rid of the problem before it gets out of hand and alo do some research on resistant varieties to try.