Plant Doctor Archive

Mildew on dahlias

I'VE had a lovely display from my bedding dahlias, but now some are coming down with a bad attack of mildew. Any tips for stopping its spread?

AT this time of year a wide range of plants show symptoms of attack by powdery mildews - a group of fungi diseases that all have similar symptoms. Late in the season, when plant growth is slowing down and the disease has spread to form large whitish patches or covers entire leaves, it's really too late to do anything. But if you spot the problem early enough in the season, when there are just a few small white powdery spots on the leaves, spraying with a fungicide such as Bravo, Super Sulphur or Nature's Way Fungus Spray will help reduce its spread.

Unlike most other fungal diseases, it tends to be worse in dry conditions, so regularly watering the foliage and keeping the soil moist will help. Weekly sprays of a teaspoon of baking soda in one litre of water plus a few drops of dishwashing detergent have proved to be a useful deterrent and some gardeners swear by regular applications of fish fertiliser to the leaves.

Next year, be on the lookout for first signs of the disease and act early - or take precautions before it shows up.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.