How do I control and identify Leaf Spots?]

Q: How do I control and identify Leaf Spots?

The question ‘Why do my plants have spotted and brown leaves?’ is one of the most asked questions by gardeners and houseplant lovers. Broadly speaking ‘leaf spot’ is caused by either a fungal or bacterial infection and, without running lab tests, it’s difficult to identify the problem. But there are differences, so get your magnifying glass out and do a bit of inspection work or you may even be able to see the differences with the naked eye.

What they look like:

If a fungal infection is present, the spots will have a white centre -  that’s the fungus growing. If it’s bacterial ‘leaf spot’, the spots will be dark brown or black and more patchy - sometimes with a yellow halo edge. In both cases if not treated, leaves will yellow, wither and die.

How to prevent them:

Prevention is always better than cure so always keep plants growing healthily. The spores and bacteria are most active when there is plenty of moisture and warm temperatures, i.e. a typical UK summer. But with warmer, wetter winters conditions are ideal for leaf spot spores to not just survive but also thrive. Reduce the areas where they snooze over winter is a great way to reduce future infections. 

  • Remove all dead leaves, weeds and debris from around the base of the plants. Do this in autumn and again in spring to tidy up any straggly fallen leaves.
  • Follow this with a mulch to prevent any splash back re-infecting the plant.
  • Clean and disinfect secateurs, gardening knives and pruning saws if you are tidying up diseased material. A simple antibacterial wipe will do the job well.
  • When planting up a garden, allow plenty of air to circulate around plants. Moving air prevents spores getting a hold, particularly in the case of vegetables and fruit.

How to treat:

It is relatively easy to sort out fungal problems. Fungicidal sprays will prevent your (or your plant’s) fungus from spreading. It will have a limited effect on damaged leaves but things won’t get worse. Sulphur sprays or copper-based fungicides can be applied weekly at first sign of disease to prevent its spread- these organic fungicides will not kill leaf spot, but will again prevent the spores from germinating so are good for controlling the spread. Remember to choose a spray that is not harmful to bees and other pollinating insects and never spray open flowers.

Keep things healthy and you shouldn’t have problems. But if you do, treat quickly and all will be good again. 

Garden Pests