HOW TO IDENTIFY IT
Black Spot is a fungal disease that is often seen on rose leaves in areas where the climate is warm and humid. It starts off as a few black spots on the leaves but it gradually spreads over the bush.
THE DAMAGE IT CAUSES
As the black spots get worse, the leaves eventually turn yellow and die and, if the problem gets too bad, the whole rose plant can die. Black spot can spread to other roses in the garden as well since the spores from one plant are carried in the breeze to other plants nearby. Eventually the plants will look yellow and quite sick.
HOW TO CONTROL IT
The best idea is to prevent the problem in the first place by making sure that the roses are really healthy and grown in a location that is not too humid. Make sure that they are fed correctly and growing strongly.
Roses need to be watered but if you water them in the evening with sprinklers that spray water over the whole bush, the area will stay very humid and the problem will get worse. Instead, use drippers underneath the plants which water just the soil and don’t wet the leaves.
Also, to help the air flow through the bushes and stop the area becoming humid, prune out branches that are in the middle of the bush. But, it is really important that you put any leaves from a diseased plant into the rubbish bin and not the compost so that the spores don’t have a chance to spread to other roses in the garden.
To toughen up the leaves on the rose bushes so that they can withstand the attack of the black spot spores, sprinkle about 100g of sulphate of potash around the base of each roses every three months and water it in well. This will toughen up their skin so the spores can’t get in.
Finally, if there’s still black spot on the leaves, head down to the local nursery to pick up a safe, organic spray for black spot on roses and spray this on the leaves as per the instructions on the bottle. Make sure that you wear rubber gloves and always get mum or dad to help you apply it.