As gardeners, we all want nothing more than healthy and disease-free plants. To minimise damage to your garden, it’s important to familiarise yourself with the possible diseases your plants are likely to suffer from so that you can take immediate action. Many common plant diseases can be prevented by improved growing conditions and by selecting the correct type of fungicide.
Botrytis: Botrytis blight or grey mould is a fungal disease that affects a wide variety of plants including strawberries, roses and grapes. It presents as a grey-brown growth on affected flowers and premature aging. To treat, remove infected tissue and any dead or spent flowers and then spray the plant with fungicide. This fungus grows in moist conditions so be sure to prune regularly to improve ventilation. It’s also a good idea to avoid overhead watering or misting and provide good air circulation between plants.
Clubroot: Clubroot is a plant disease that affects broccoli, brussel sprouts, turnips and other plants belonging to the mustard family. The disease deforms and rots the roots, causing them to have a swollen, lumpy and wilted appearance. If not caught early and handled properly, the disease can release spores which can remain in the soil for many years. When you encounter clubroot, firstly burn and remove the affected roots. Then analyse how you can improve drainage - one way might be to plant brassicas in pots first before planting out. To prevent future clubroot infestations, add lime with a pH of 7.5 to the soil. You’ll also need to be particularly vigilant with controlling weeds.
Fungal leafspot: Leaf spots are easily seen, presenting as black spots on roses. Spots and blights also commonly appear on tomatoes, potatoes, carrots and many shrubs. Remove the affected leaves and investigate what type of fungicide you’ll need to use. For most plants, you’ll need to use a spray which contains lime sulphur or Mancozeb. On roses, you’ll need to use a specialist Rose Black Spot and Insect Killer spray.
Powdery mildew: This fungal disease coats the leaves in a dusty white or grey powder, usually appearing on the upper sections of the plant first. It’s a common disease of roses, dahlias, calendulas and vine crops. In addition to removing affected flowers, leaves or stems, spray the plant with fungicide and prune, mulch and water the plant regularly.
Rust: Rust fungus is easily identified by the many orange coloured pustules that appear on leaves or stems. Rust fungus grows within the leaf so there are usually spores on the underside of the leaf or stem as well. It’s a common disease of geraniums, roses, calendulas, beans and gerberas, attacks turf and is a serious disease of poplar and willow trees. To treat rust, pick off the affect leaves and spray the plant with a fungicide such as Macozeb or lime sulphur. Also avoid wetting foliage and prune regularly to improve air circulation.
Viruses (ringspot) : Viruses can cause numerous symptoms and commonly cause browning or yellowing leaves or flower colour. They are generally transmitted between plants by aphids and other sap sucking insects so it’s important to control disease-carrying pests. There are no cures for virus disease so you’ll need to destroy all infected plants to reduce spread. Also observe good garden hygiene, paying attention to drainage, air circulation and mulch regularly.