This rose disease is unsurprisingly known as "black spot". You'll know when it strikes because circular black spots with lacey edges appear on the plants' leaves, eventually causing them to turn yellow. The remedy: Remove and discard the infected foliage and any fallen leaves around the rose. Artificial sprays may be employed to prevent or treat this sort of rose disease.
2. Stunted or malformed young canes
This is commonly known as "powdery mildew", a fungal disease that covers leaves, stems and buds with a white powder, transferred on the wind. It causes the leaves to curl up and grow purple. The remedy: Spray with Funginex or Benomyl to treat this fungal disease.
3. Blistered underside of leaves
Known as rust, this disease is characterized by orange-red blisters that turn black in autumn. However, it is hardy and is capable of surviving the winter, ready to attack new sprouts in the spring. The remedy: Carefully collect and discard leaves that are infected in autumn and consider spraying with a Benomyl or Funginex spray every 7-10 days, as this may help.
4. Malformed or stunted leaves and flowers
This disease is caused by spider mites, which are tiny yellow, red or green spiders found on the underside of leaves where they suck out the juices from the plant. The remedy: The application of Orthene or Isotox may help in treating this infestation.
5. Weak and mottled leaves with tiny white webs under them
Aphids cause this problem. They are small soft-bodied brown, green or red bugs. They often congregate under leaves and flower buds, where they suck out the plant juices from tender buds. The remedy: Malathion or diazinon spray may help roses to survive these insects.
6. Flowers that don't open or are deformed when they open.
"Thrips" could possibly be the reason behind this problem. They are slender, yellow-brown insects with fringed wings, that, like the other infestations mentioned, aim to suck out the juices from flower buds. The remedy: Remove and discard the infested flowers and consider an application or two, of Orthene or Malathion, which may help to combat this trouble.
Finally, remember that roses are hungry feeders that require a lot of fertilizer to become and remain the beautiful, healthy bushes you chose them for.
