This fungal disease affects rose foliage and sometimes the stems too and can reduce vigour and flowering. It appears as black spots on leaves, which turn yellow and fall. It is caused by a fungal pathogen, and it thrives in wet and humid conditions. The fungal infection occurs when water is left on the plant foliage especially at night, as the leaves don’t get a chance to dry.
Black spot is an ongoing disease once it appears, especially in areas of high humidity and rain. So, understanding the disease and helping to prevent it is the key to controlling it. Start in the winter by pruning the bush and removing diseased and damaged foliage. This also allows air movement around the bush. Remember to clean your secateurs between pruning each bush by dipping them into bleach, as this will help stop infection.
Once the bush has been pruned, spray it with Sharp Shooter Lime Sulphur. This forms a protective film of sulphur which prevents the entry of fungus into the plants. Continue to spray if humid and wet conditions are around. Check plants when out in the garden and remove diseased foliage before it takes hold.
In spring and summer if black spot does occur there are natural remedies including making your own spray. Try mixing two teaspoons of bicarb soda in 5 litres of water, with a couple of drops of Seasol, or mixing one part milk with two parts water into a spray bottle. Shake and then spray onto the leaves weekly. Reapply after rain.
If the disease has taken over your rose garden and a commercial fungicide is required, try EarthCare Black Spot & insect spray. It’s a combination spray that kills and controls fungal diseases such as black spot, powdery mildew, rust and insects such as aphids, thrips, caterpillars, budworm and mites on roses and flowering plants. When spraying the foliage follow the directions on the back of the pack and spray both sides of the foliage. Repeat application maybe needed for further control. Remember not to spray when beneficial insects and bees are around.
A healthy garden can also help prevent disease infestation. If your plants are strong and healthy, they may be able to handle and reduce the stress of pests and diseases. Applying Seasol regularly every two weeks during the year can help them to cope with environmental stress. Keeping plants fed with fertilisers such as PowerFeed All Purpose including Natives or PowerFeed PRO SERIES Roses & Flowers, better watering and appropriate light exposure can also help build tougher plants.