Pests and Diseases

The plants we love to eat are also popular with other garden inhabitants.

Finding that your new seedlings, so carefully planted out, have disappeared overnight thanks to the

resident army of slugs and snails is guaranteed to ruin your day.

Losing your beautiful crop of fruit to blackbirds is enough to make you weep!

And what about those unsightly spots on the zucchini leaves? Or the lumps on the lemon tree


There are things you can do to diagnose the problem and minimise the losses.


Snails and slugs are probably the most common problem. The most efficient means of control is

to get out in the evening, particularly after rain, with a torch, a disposable glove and a bucket.

Collect the snails and slugs then then kill them quickly by pouring a kettleful of boiling water over

them. Next morning bury them in the garden - they are very nutritious!  Alternatively, use scissors:

a very efficient murder weapon for those small but destructive slugs that are too slimy to pick up.

You could also try copper tape around the edge of the garden bed or bowls of beer set into the soil

so the top lip of the bowl is level with the soil.

Blackbirds like to scratch around in fertile garden beds, although they don't usually bother when

the bed is densely mulched with straw. They will, however, enjoy your tomatoes if they find them,

as will lorikeets, Indian mynahs and parrots, and the only really effective way to keep them away

is by netting the plants.

Possums love fruit, and may find your vegies. Again, netting is the best way to keep them safe.

Cabbage white butterflies lay their eggs on brassicas (broccoli, cabbage,kale etc). The green

caterpillars can make a mess of these plants. 'Dipel' is a pesticide that is registered for organic

produce, and if sprayed every 2-3 weeks will control these nuisances. Otherwise, cover your

brassicas in fine netting, or grow them in the cool months when the butterflies are not


You may find aphids or white fly or passionfruit leaf hoppers invading your garden at times

over summer. There are pesticides such as eco oil, pest oil and pyrethrum that can be used in an

organic garden, and a dilute solution of detergent will help too.

Encourage predator insects by growing plenty of flowering plants, and letting some of your herbs

and vegetables flower. Lettuce, silverbeet, parsley, dill, coriander, parsnip, oregano, thyme and

marjoram are all popular with predator insect species. And you will be able to collect seed for the

next crop.

Citrus Gall Wasps

Galls on lemon tree
An unusual gall on the vein of a citrus leaf
Last season's gall: the holes show that the wasps have hatched

These tiny wasps lay their eggs into the bark of the new growth on citrus

trees. Lemons, limes, grapefruit and Japanese seedless mandarin are particularly susceptible.

The growing wasp larvae form swellings - galls - on the stems of the citrus trees. They hatch out

in August/September and will go on to produce new generations of larvae. Without the diligent

removal of the galls, trees can become heavily infested which will weaken them and reduce


Check each tree several times, in different light conditions: it's easy to miss the galls. Prune them

out; a severely infested tree may need to be cut back hard - it will regrow, but don't expect much

fruit for a couple of years.

Ensure the growing wasps within the galls are killed: submerge prunings in water for several

weeks; microwave or bake the galls. Shredding in the mulcher then composting in a hot heap

should do the trick too.

Sap-sucking Bugs

Bugs are sap-suckers. they can cause

considerable damage to plants, and those that

favour fruit and vegetables are particularly


On the top right is a nymph of a Spined Citrus

Bug. In adult form they have conspicuous spines

just behind their heads. They cause citrus fruits to

drop prematurely, and leave damaged spots in

the fruit.

Below right are nymphs of Green Vegetable

Bugs. As adults they are in fact green. They

cause scarring on tomatoes and leave beans

limp and sorry.

Spraying the bugs directly with a detergent

solution will quickly kill them while they are still

juveniles. Adults are tougher, and picking them

off by hand can be more effective.