Key takeaways
- Box blight causes brown patches, leaf drop and black streaks on stems, and spreads in warm, damp weather.
- Pimply, curled new leaves on lilly pilly are usually caused by psyllids.
- Report suspected myrtle rust to MPI rather than touching it.
Box blight
Affects: buxus (box) hedges and topiary.
Signs: leaves turn brown and drop, leaving bare patches, with black streaks and dieback on young stems. In wet weather you may see white fungal growth under infected leaves.
What helps: the Royal Horticultural Society advises trimming only in dry weather, cleaning tools between gardens, raking up fallen leaves and bagging infected material rather than composting it. A slightly rounded top and less frequent clipping keep air moving through the hedge. Badly affected plants are best removed.
Lilly pilly psyllid
Affects: lilly pilly and eugenia (Syzygium) hedges.
Signs: new leaves that curl, bubble and look pimply or pitted. The damage shows up on the fresh red growth.
What helps: regular trimming of new growth reduces psyllid numbers and removes damaged leaves, which won't recover. A horticultural spray oil on new growth in spring can also help. Follow the label and spray in the evening to protect beneficial insects. Keeping the hedge watered and fed reduces stress.
Myrtle rust
Affects: plants in the myrtle family, including lilly pilly, pōhutukawa and ramarama.
Signs: bright yellow or orange powdery patches on new leaves and shoots.
What helps: don't touch it. Take photos and report it to the MPI Exotic Pest and Disease Hotline on 0800 80 99 66. Trimming myrtle hedges in winter reduces the risk, because new growth is less likely to get infected in cold weather.
Sooty mould
Affects: many hedges.
Signs: a black, sooty coating on leaves.
What helps: sooty mould grows on the sticky honeydew left by sap-sucking insects such as psyllids. Dealing with the insects is the fix.
Pittosporum psyllids
Pittosporums can get their own psyllid that pits and curls new leaves, much like lilly pilly. Trimming off affected growth helps.
Prevention
- Trim in dry weather.
- Clean tools between hedges, especially between gardens.
- Don't compost diseased clippings.
- Keep hedges watered and fed through dry spells.
- For new hedges, choose plants that are less prone to problems. See the best hedge plants for Auckland.
Need your hedge trimmed and the clippings taken away? See hedge trimming.