One of the rather worrying things for many gardeners is the strange things you see on your plants. Leaves, branches and even fruit can develop pimples, lumps, bumps and all sorts of horrible things which can be very confusing.
Generally lumps and bumps on plants are called galls. In most cases they are actually caused when an insect such as a wasp or small fly lays its eggs in the stem or leaf of a plant. The plant tries to deal with the intrusion by forming a bump around the damaged area.
Native plants seem to be particularly susceptible to gall problems as there are many native insect pests which live out their lives on these plants.
To help you sort out the lumps and what to do about them here are some of the galls most commonly seen in the garden.
Wattle trees sometimes produce something that looks like some sort of seed capsule. Well it isn’t. It’s a problem known as acacia flower gall and is caused by a tiny wasp.
What to do: Don’t worry about it because it doesn’t do any harm to the plant. If the lumps offend, you can always cut them off and put them in the garbage.
Gum trees seem to produce all sorts of little lumps on their leaves and sometimes on their stems. However none of them will ever seriously damage the gum tree. They’re part of the ecology of the gum tree – formed by tiny insects that live in, on and around your tree.
What to do: Ignore them is all you need to do. There is no need to use any chemical to get rid of them. Indeed, having a chemical free environment will encourage more insects and birds into your garden and so bring these pests into line as others come to feed on them.
Lillypillies are very popular plants in gardens at the moment and some species can give you some dreadful problems. The most commonly grown lillypilly is Syzygium australe and its cultivars. Many of these plants develop terrible pimples on their leaves, particularly on the new growth. The pimples are caused by a small insect called a psyllid and are the plant’s reaction to the insect pest’s attack.
As lillypillies are grown mainly as foliage plants (for hedging and topiary), lumps on the leaves are a problem as they are unsightly and spoil the plant’s effect in the garden. There are other species of lillipillies which don’t seem to be affected by these pimple like lumps.
What to do: As lillypillies are used as ornamental foliage plants you really do have to control the cause of the lumps if you want the plant to look any good. For this reason ‘Burke’s Backyard’ doesn’t recommend planting Syzygium australe or its gall-prone cultivars, (‘Blaze’ and ‘Lilyput’ are particularly susceptible although ‘Tiny Trev’ appears to be resistant) but if you’re stuck with one and you want its leaves to look good, it is necessary to spray with a systemic insecticide containing dimethoate (such as Rogor or Folimat). These sprays will kill the insect pest and so stop the plant from forming galls on its leaves.
If you are trying to attract birds to your garden however you may not wish to use insecticides and there is an alternative approach: don’t plant the affected species and varieties. Search out lillypilly species that are not attacked by the pest. Both Syzygium leuhmannii and the closely related Acmena smithii, do not appear to be attacked by the psyllid and so do not need to be sprayed.
Do remember though when you’re buying a lillypilly at the nursery it will have clean foliage. These plants will most likely have been sprayed while they were being grown so will not exhibit the problem. When you get the plants home and stop the regular spray program, the galls may appear on the new growth.
The native daphne, Pittosporum undulatum, is a real martyr to lumps and bumps and its leaves can become quite distorted and very unattractive. The culprit here is a native fly that lives in and around native daphnes.
What to do: This pest is extremely difficult to control without the use of systemic insecticides but, as it is a background tree, not one you’re looking at close up that is grown for its beautifully perfumed cream flowers, it is possible to ignore the problem. It’s never going to kill the plant and the flowers are unaffected.
Citrus trees also suffer galls which are seen as lumps along some stems. These lumps are caused by a pest known as the citrus gall wasp.
What to do: It is highly recommended to break the cycle of citrus gall wasp infestation by removing affected stems before the end of August (after this time the insects emerge from the gall). Dispose of prunings in a plastic bag and then into the garbage bin.
Don’s bottom line
The bottom line of all this is, if you’ve got lumps and bumps on any of your plants and if these offend you trim them off and put them in the garbage, it’s that simple.