Sub-tropical and tropical climates provide the perfect humid conditions for fungal diseases such as powdery mildew and black spot to thrive.
These fungal diseases can severely stress the plant and diminish its performance, resulting in fewer blooms and a sickly looking plant. However, natural treatments are available to assist gardeners in fending off these fungal infestations.
What is powdery mildew
Powdery mildew appears on new foliage and buds, first as a series of small white spots, which later become a furry mass of mould. It causes the leaves to wilt and wither and eventually die.
What is black spot
Black spot shows on older leaves as dark, circular marks and eventually the foliage turns yellow and falls to the ground.
Natural treatments for powdery mildew and black spot on roses
Treatment 1: Lime Sulphur
Dilute lime sulphur with water to the manufacturer’s recommendations and spray over the stems and trunk. Apply this in the winter when the plant is dormant.
Treatment 2: Milk and Baking Soda
Organic growers have used milk and baking soda with success. Simply mix half a litre of milk with two tablespoons of baking soda in five litres of water and spray liberally over foliage and stems. This formula can be applied at any time of the year.
Treatment 3: SeaMax® Fish & Kelp
Rose Growers love it so much that SeaMax® Organic Fertiliser Liquid is officially endorsed by The Qld Rose Society. This BFA certified organic product not only prevents fungal disease, but also fertilise your plants at the same time. Simply mix in a watering can to the manufacturer’s recommendations, then liberally water over the foliage and stems.
Tips for decreasing rose fungal diseases
Tip 1: Spacing
When planting roses, they must be far apart to allow for good air circulation all around. They should be planted in full sun away from other plants that will smother their stems and compete for moisture and nutrients.
Tip 2: Hygiene
Practice good hygiene by; cleaning secateurs with a solution of bleach and water between each rose bush; never compost prunings; and remove any fallen foliage, especially if it is diseased.