Plant Doctor Archive

 MY husband has cancer and because I don’t want to use any chemicals in my garden, I have been trying to manage my plants organically. The roses were looking pretty good but over the last two weeks they have been attacked by black spot. I’m picking off the worst leaves and hoping for the best, but do you have any ideas for organic ways to prevent black spot (and rust too, which I usually have to contend with later in summer). Thank you very much.

  BLACK spot is most prevalent in wet humid weather, while rust usually is more of a problem later in summer when the weather is drier. In your case the best way to minimise the effect of both diseases (as well as powdery mildew, which can also be a problem on roses) is a combination of good gardening practice and the use of organic sprays. Try the following:

• In winter, when pruning, collect up all fallen leaves and prunings — burn or put in the rubbish, don’t compost them.
• Make sure your plants are well spaced or prune them to allow lots of air flow through and around the plants.
• Before new growth starts in spring, spray the plants thoroughly with a copper fungicide such as Super Copper or copper oxychloride.
• During the growing season, keep them well-watered and fed. Use a specific rose fertiliser in order to avoid soft lush growth. And avoid wetting the leaves when watering.
• As soon as black spot appears, pick off affected leaves to reduce its spread.
• For mildew and black spot, try spraying during the growing season with an organic spray such as Nature’s Way Fungus Spray.
• Plant disease-resistant varieties, like the Flower Carpet series.

Weekend Gardener, Issue 136, 2003, Page 35

• The views expressed here are not necessarily those of the RNZIH
• Content or advice may be out-of-date.