SAFE SPRAYS FOR BLACK SPOT

Question

Our ‘Granny Smith’ gets this spotting on the fruit; the ‘Sturmer’ seems to be okay. The tree overshadows the summer vegetable garden so I’m loath to use anti-fungus sprays due to the waiting period after spraying before you can eat the vegetables. Would love some advice on what is the safest spray to use.

L. Smith, Lower Hutt

Answer

There are a couple of diseases that can cause damage like this to apples. The main one is black spot, also known as apple scab; the other is glomerella. Both diseases cause leaf spot symptoms along with damage to fruit, and ‘Granny Smith’ is a particularly susceptible cultivar. They’re relatively common diseases in many parts of the country, but worse in regions where rainy spring weather is the norm, as moisture encourages the fungal spores to germinate on leaves upon infection then spread to developing fruit. Spots appearing on the leaves in spring and early summer are early symptoms of infection by black spot.

Fortunately the treatment is much the same for both diseases. In autumn, remove any mummified fruit left on the trees, rake up leaf litter and old fruit from under them, and burn it or put in the rubbish to be buried in landfill. In winter, prune out any dead or diseased-looking wood then give the trees a thorough spray with a copper fungicide, such as copper oxychloride or one of the ‘liquid copper’ products available in garden stores, or Kiwicare Organic Super Sulphur. In spring, as soon as leaf buds start to break and new leaves appear, spray again with the copper or sulphur product, or Yates Fungus Fighter. For good protection, you may have to spray every 7–10 days or so until fruit has set, perhaps even longer if the weather is wet. As far as eating your vegetables is concerned, the withholding period (minimum length of time that must elapse between application of an agricultural chemical and harvest) for liquid copper and Super Sulphur is nil, and for copper oxychloride it is one day. Note, Yates Fungus Fighter should only be sprayed on apples in early spring and not after fruit set (when young fruits form). Make sure to read and follow the product label recommendations.