Powdery mildew
What is it?
Common disease caused by several species of related fungi which infect a wide range of plants including cucurbits, grapes, strawberries, some fruit trees, and ornamentals such as roses, gerbera and calendula. Spores can be spread by wind and rain. The fungus grows best in warm humid conditions and/or crowded conditions with poor air circulation. It grows on the surface of plants but not on dead tissue.
What to look for
- White powdery spots on leaves that spread to cover the entire leaf surface.
- Distorted and curled leaves with powdery covering.
- Some yellowing of older leaves.
What to do
- Avoid wetting leaves when watering, especially in warmer months.
- Prune plants to improve air circulation
Spray:
Lime sulphur, wettable sulphur and garden fungal sprays such as Yates Rose Gun or Hortico Rose Spray. Follow directions.
Petal blight
What is it?
A serious fungal disease that infects flowers and buds. Periods of frequent rainfall or misty weather that coincide with flowering time will greatly accelerate the rate of infection. Blighted flowers first exhibit small spots which enlarge rapidly to engulf the flower, causing it to become slimy and limp. Infected areas of flowers soon become tan or light brown, and eventually, entire flowers turn prematurely brown. Infected flowers dry and cling to the plant longer than healthy flowers do.
What to look for
- Watery spots on petals. Slimy petals are also an unmistakable symptom.
- Dry flowers stuck on bush.
What to do
Hands on:- Promote good air circulation around your plants, either by pruning or by spacing plants properly when planting.
- Avoid overhead watering, as spores may spread on water splashes.
- Pick off diseased flowers and dispose of them. Wash hands before touching healthy flowers.
Mancozeb. Follow label directions.
Rose black spot
What is it?
A common fungal disease that is specific to roses. The disease initially appears on lower leaves, but will later spread to the rest of the plant’s leaves if not kept in check. Initial symptoms are leaf spots, then the leaf tissue around the spots slowly turns yellow and defoliation follows. Spores can over-winter in infected leaves and stems, and germinate in spring when conditions are favourable. New infections occur on leaves that have been damp for several hours.
What to look for
- Fringed dark brown or black leaf spots.
- Yellowing and falling leaves.
What to do
Hands on:Pick off infected leaves and dispose of them in a plastic bag in the rubbish, not your compost bin. Prune roses in winter to promote better air circulation and reduce humidity.
If your roses were infected in the spring, dispose of these prunings in the rubbish. Disinfect secateurs afterwards. Avoid wetting leaves when watering.
Spray:Potassium bicarbonate, Mancozeb, Triforine or garden fungal sprays Yates Rose Gun or Hortico Rose Spray. Follow label directions as more than one application may be required.
