bugs and pests

Summer pests & diseases checklist

By Jennifer Stackhouse

Tags: azalea lace bug, black spot, cabbage white butterfly, caterpillar, Disease, fruit fly, fungal disease, green caterpillar, mildew, Pest, plant disease, Rust, slug, snail, summer pests, two-spotted mite, whitefly

There are many tiny critters and plant diseases that want to feed on your plants over summer. Here’s our checklist for summer nasties, along with quick and easy ways to stop them in their tracks.

The quickest way to deal with many pests and diseases is to remove the pest or damaged plant part by hand when it’s first seen. This may mean squashing a pest or removing an infected leaf or flower.

When an insecticide or fungicide is called for, always follow the directions on the container (even for organic products). These instructions will indicate the amount to apply and the frequency of application. Often repeat applications are required. Always check that the product you’re using is suitable for your plant (some pesticides are not registered for use on edibles). Avoid applying any pesticide when beneficial insects and bees are present and during very hot or windy conditions.

 

Azalea lace bug

Check azalea and rhododendron leaves for signs of azalea lace bug. A dull mottling, silvering or whitening of the leaves is indicative of this pest. It’s a very small insect with lacy wings and may be seen under affected leaves. Apply Confidor or an organic soap spray to the underside of the leaves to kill the bug. Leaves will remain discoloured until they’re discarded however new growth should be free of the pest and hides old damage. Make a note to spray new foliage next spring after flowering to prevent attack.

Caterpillars

While some caterpillars turn into beautiful butterflies, many that attack garden plants and vegetables are pest species, especially the green caterpillars of the cabbage white butterfly. Spray hungry caterpillars on herbs, vegetables and ornamentals such as geraniums with Dipel, a specialised biological control for caterpillars or Success Ultra (a naturally derived insecticide). Vegetable dust can also be applied to treat caterpillars. Liberally cover affected leaves with the ‘dust’ but wait at least one day before harvesting treated vegetables.

Fruit fly

This is the number one summer pest of soft fruits and vegetables including tomatoes, capsicum and stone fruits. Small maggots feed inside the fruit causing it to rot and fall. Early signs include sting marks on the skin. Pick up or remove damaged fruit and dispose of in a sealed bag in the garbage (not the compost). Use fruit fly baits and lures to control numbers. These organic products are highly effective but must be replaced often, especially after rain.

bugs and pests
Pictured left to right: Azalea lace bug, cabbage moth larva munching on foliage, fruit fly close up

Fungal diseases

Rust, mildew, black spot and other fungal diseases of foliage and flowers occur on roses, fuchsias and other ornamentals and on some vegies over summer. Fungal problems can be controlled with a registered fungicide. When applying a fungicide to edibles, check the withholding period before harvesting from the treated plant. The withholding period is the length of time that must elapse between applying spray and harvest. There are specific fungicides for some plant diseases along with general fungicides such as copper, copper oxychloride and salts of potassium (sold as Eco Rose), which treat a wide range of diseases.

Snails and slugs

These slimy leaf munchers are often prolific after rain and at night but can decimate new growth and seedlings at any time. Apply an organic snail bait to lure them away from precious plants. Iron-based snail baits are pet and wildlife friendly, when applied at the recommended rate.

Two-spotted mite

This tiny insect feeds under the leaves of both edible and ornamental plants causing silvering to the leaf surface and leaving obvious webbing and frass (insect poo) under the leaf. Under a magnifying glass the two spots on its abdomen (that give it its name) are visible. They are often found in large numbers on plants that are stressed by too much shade or that are kept too dry. They can attack beans, indoor plants, azaleas and rhododendrons, viburnum, fuchsia and many other plants. Apply a systemic insecticide or spray under the affected foliage with a miticide such as Natrasoap (suitable for edible plants).

Whitefly

This tiny white insect may occur in large numbers and fly up when disturbed. Whiteflies are found on herbs, vegetables, indoor and foliage plants and other ornamentals. Treat with an organic pesticide such as Natrasoap (also suitable for edible plants).

bugs and pests
Pictured clockwise from top left: powdery mildew, snail, two-spotted mite, the effects of whitefly.

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Jennifer Stackhouse

Jennifer Stackhouse

Horticulturist, garden writer, blogger & editor.