Tui Garden

Pests and Diseases

Previously classified as plants, fungi are now recognised as a distinct group of organisms. They do not contain chlorophyll and are therefore unable to manufacture their own food. The result is a lifestyle built on being saprophytic, when they are dependent on dead tissue, or parasitic, when they survive off the kindness of others.

Most fungal diseases will leave garden plants struggling to survive, and may even cause their death. In their weakened state, affected plants also become susceptible to bacterial and viral diseases.

Fungi are encouraged by humid weather and spread via spores, which are usually carried in water or by wind. The spores may also be transferred from plant to plant by insects, so eradicating an insect pest may also eradicate the fungal disease.

All infected leaves, stalks and plant material should be disposed of by burning or throwing it out in the rubbish.  Don't throw the material in the compost as the fungi will thrive in the warm conditions.

Fungal Diseases

  • Chocolate spot

    Chocolate Spot

    Peculiar to broad beans, this disease tends to affect autumn-sown plants grown in poorly drained soil. Brown spots can affect the leaves, stems and even the flowers, and the whole plant may subsequently die. Plants grown through the winter are most vulnerable, and those that are affected need to be sprayed or pulled out.

  • Club rot


    Clubroot attacks brassicas, especially if the soil is poorly drained and too acidic. Watch out for plants that have small leaves, bad colour and swellings on the roots, which will eventually decay. This disease persists in the soil and, ideally, you should not replant brassicas in an infected patch of land for another four or five growing seasons. If you have concerns, raise seedlings in sterile seed mix and dip the roots in a fungicide before planting out.

  • Dampning off

    Damping-off disease

    This disease will cut a plant down early in life. The stems turn black and shrivel at soil level, then the plant starts to suffer because its basic water and nutrient flow is being strangled at the very base of the stem. Avoiding overwatering is rule number one. Second, use good-quality sterile soil and keep up a good airflow. A copper-based spray can be applied, but it may be overkill for this problem.

  • Potato tomato phsylid

    Potato/tomato blight

    Potato blight is what wiped out a legion of potatoes in Ireland in the mid-1800s. It appears on tomatoes and potatoes, especially when the weather is hotter and more humid than normal.

    Large, dark brown spots appear on the leaves of infected potatoes, which then become distorted and yellowy, and the plant begins to fail. In tomatoes, it leaves the fruit hard, spotty and unusable. Blight is a serious disease and needs to be dealt with quickly.

    Pick off any dead and dying leaves before treating the plant with spray. Blight can be treated with copper-based sprays or a really strong fungicide. Alternatively, try a garlic spray and repeat the doses every seven days.

    Mulch your plants really well with pea straw or well-rotted seaweed and try sprinkling Tui Lime under each plant. Remember to rotate your crops: don’t plant tomatoes, potatoes or beans in the same spot each year.

  • Powdery mildew

    Powdery mildew

    Powdery mildew gets its name because it looks like a dusting powder on your plants and flakes when touched. It attacks when the soil is dry and the air humid. The whole plant can be coated in the powdery residue. The leaves and skins of plants like cucumbers, courgettes, melons, pumpkins and silver beet can all be affected.

    Use Tui Disease Control for Fruit & Veges to stop further spread. Space plants so that the air can move freely, rotate crops properly so the mildew is not spread further, and keep the soil moist during dry periods. Spraying with a weak vinegar solution also helps.

  • Wilt


    This disease is caused either by Fusarium or Verticilium fungi, and causes leaves to turn yellow and wilt. It is prevalent in warm climates and can be spread by beetles from plant to plant.
    Wilt is best destroyed by burning the plants.
    Crop rotation is not effective and the only solution is to grow disease-resistant varieties.

It is not a straightforward matter to classify insects into ‘good’ or ‘bad’, as many can be both a nuisance and a benefit in the garden. Insects can play a vital role in the production of fruit and preservation of the foliage surrounding it, but keeping large infestations of any type of insect (except honey bees) controlled is important.

Insect Identifier

  • Aphids


    All plants can be attacked by aphids. Remove the food source and they will simply find somewhere else to live. Green, brown, pink, black or yellow, aphids weaken plant growth by sucking out the juices. They cause plants to lose vigour and collapse, and new shoots to wither.

    Aphids quickly multiply in hot and humid conditions, and there are even hardy types that like cold conditions. Control with Tui Insect Control for Fruit & Veges or Tui Insect Control for Flowers at the first signs of them attacking plants. Make sure to spray both the top and underside of leaves.

    New spring growth on citrus, stone and pip fruit, plus most berries, are particularly susceptible to aphid plagues.

  • Codling Moth

    Codling moths' favourite plants include apples, nashis and pears, plums, walnuts, peaches and nectarines. Codling moth larvae can completely destroy crops as well as expose the plant to further attacks from bacteria and fungi.

    The fully grown caterpillar likes to hide over winter under the bark of a tree. By mid-spring it goes to a chrysalis where it changes into a winged adult moth, emerging at the exact time of flowering for most pip and stone fruit. Adult fertilised females will lay eggs in developing apples. The caterpillars burrow into plump fruit, causing ‘maggoty’ apples.

    Control often involves pest control to repel all stages of the moth (different regions of New Zealand have different times for each stage of the cycle). Check sprays carefully before applying, as some harmful sprays may kill bees required for pollination. Codling moth traps will use pheromone scents to attract the adults to a sticky trap. If the infestation is large on particular trees, it might pay to stick to a spray programme and then, once the tree and fruit have come back to life, try less harmful methods.

    Larvae can also be trapped as it crawls over the trunks and branches of the tree. Wrap pieces of corrugated cardboard around the limbs so you can pinpoint the location of the larvae. These pieces of cardboard can be burnt and replaced weekly to slowly rid the tree of the initial problem. Pyrethrum and peppermint are also reportedly beneficial to spray onto the fruiting tree.

  • Grass grub beetle

    Grass grub beetle

    Often described as brown beetles, these grubs are native to New Zealand and cause much damage to grapes, cherries and chestnut trees. Although the grubs happily eat grasses and the roots of small shrubs, thanks to horticultural and pastoral plantings they have also developed a taste for nearly all fruit tree roots.

    The adults will hatch between October and January, depending on where you live, and are often found wandering near a barbecue or glowing candles in the evenings, attracted by light. Adult grass grub beetles can devour a range of foliage and fruit, causing raised bumps on the outside of the fruit skins. The females lay eggs in the soil to pupate over winter, ready for the change in temperature.

  • Green vegetable bug

    Green vegetable bug

    These big, fat, green bugs that like to walk all over your garden are sometimes called stink beetles or green shield beetles. Green vegetable bug families will invade a whole plant. Hard, corky growths on tomatoes and tamarillos where the fruit has been pierced are evidence that green vegetable bugs have been around.

    The best method to deter the infestation, though not for the squeamish, is to squash one bug.

  • Leaf roller caterpillar

    Leaf roller caterpillar

    There are a number of different caterpillars that roll, web and tie up leaves on fruit trees. Typically, the adult moth lays eggs and the larvae that hatch out can damage the leaves, fruit and buds of plants. Young larvae are found on the tips of new leaves, where they make a silk web that rolls the leaf into a tube. Leaf rollers are difficult to control because they are so well protected by the leaves they roll up in.

    Pesticide sprays can be used. Ensure the plant is thoroughly sprayed to treat bad infestations. These are best applied in autumn rather than spring, to avoid harming beneficial insects at blossom time. Parasitic wasps will eat the caterpillars and pupae and it is also effective to squash by hand any caterpillars you see. Organic sprays like neem oil are beneficial if applied regularly.

  • Lemon tree borer

    Lemon tree borer

    Lemon tree borer can cause a lot of bother to fruiting crops. They appear at night when they fly about looking for mates, but can go looking for lights so will end up in outside candles and light features. They will attack plants, such as citrus, grapes, walnuts, gooseberries, figs and tamarillos, and they have a particular fondness for citrus wood.

    The adults can be found any time between spring and summer. This is the reproductive stage of their life cycle. They lay their eggs on branches and twigs and on hatching, the larvae bore into the stems. A good sign that your citrus is under attack is a light sawdust falling into the cracks and bottom of the tree.

    The borer is difficult to control with sprays because larvae are well protected by the stems of the plant. Pruning back branches that are infested is the only method to prevent the borer from spreading. In severe cases, where the whole plant is affected, the plant will have to be removed and destroyed.

  • Scale


    Scales are hard, cuticle-covered, rapid-breeding insects found on the bark, leaves, stems and roots of a wide range of ornamentals where they suck up the sap. They exude a sticky honeydew that attracts ants and other insects. They can come in an array of colours and shapes, somewhat confusing the gardener.

    A scale attack will debilitate and eventually kill a plant by sucking the sap. Their strength, however, is in their water-repellent coat. Water-based insecticides are not absorbed at all and so are ineffective against scale. The only control methods to work well previously were systemic insecticides containing heavy-duty chemicals, which were taken up by the plant. Insecticides such as these may destroy other more garden-friendly insects.

    An eco-friendly alternative is to spray three times at monthly intervals with a natural-based spray such as Tui Insect Control for Fruit & Veges. Repeat sprays may be needed. If a plant has had a massive influx, it sometimes pays to pull it out and burn the plant material.

  • Spider mites

    Spider mites

    Spider mites are tiny and can attack the foliage of apples, plums and other fruit trees, sucking sap and causing leaves to turn a mottled yellow and fall prematurely. Mites favour hot summers. There are many different types of mites, including the the European red mite and the two-spotted spider mite, red spider mite (pictured left), and the apple spider mite.
    For gentle eradication, predatory control is a favoured option: ladybirds will hunt out tiny mites, and some more harmful mites can be hunted out by other members of the mite family. Be aware that miticides contain strong chemicals, which can wipe out many different types of spider mites whether or not they are harmful. Neem oil is a good alternative. Regular sprays are beneficial but beware – some mites can become conditioned to the spray.

  • Vinegar fly

    Vinegar fly

    Vinegar flies are a large family of insects grouped together under their common fondness for eating decaying fruit, and with the ability to quickly fly from fruit to fruit – and away from swatting hands. They breed every 2 or 3 days – the reason why there are always plenty around.
    The best way to remove vinegar flies before they plague every piece of fruit in your house and garden is to remove the food source. Cover the fruit bowl or keep fruit in the fridge. Discard any old and rotting fruit immediately; cut any rotting fruit from tree branches, and dispose of any fruit that drop to the ground. Vinegar flies can also be trapped with simple vinegar traps. Vinegar flies will only appear where rotting fruit exists.

  • Whitefly


    These are tiny, white, moth-like and incredibly destructive pests. Both the adults and the larvae are sap feeders and cause damage similar to that caused by aphids. They have the potential to inflict significant damage if not controlled.
    They can be controlled by spraying with Tui Insect Control for Fruit & Veges and Tui Insect Control for Flowers. Frequent applications will be necessary if a heavy infestation has developed. You could also try garlic spray, or a few dressings of neem oil, or even soapy water from the washing machine.
    A good spray with a hose every day up and under the leaves can help deter the whitefly from settling, and chemical-based sprays applied in autumn can kill the larvae and therefore stop the spread.