Summer Insect Control

The Usual Culprits

Ranked by Kiwi gardeners: these are the 'most-searched online' summer pests

• Passionvine Hoppers
• Whitefly
• Mealybugs
• Codling Moth & Oriental Fruit Moth
• Aphids
• Thrips
• Mites
• Caterpillars
• Scale
• Pear & Cherry Slug
• Lemon Tree Borer
• Tomato Fruitworm
• Earwigs
• Tomato-Potato Psyllid

Sucking insect pests love to feed on sweet and sugary plant sap. This depletes important nutrients from your plants. These nasty little suckers can cause leaves to permanently discolour and distort, or even transmit plant viruses.

To add insult to injury, sucking insects excrete a substance called honeydew, which invariably gets covered in unsightly sooty mould. Sooty mould appears as an ashy black layer, that covers leaves and stems. Honeydew will also attract ants, which you can often see travelling up and down plant stems to collect the sweet booty.

Chewing insects like caterpillars and beetles continue to be a pain in summer; they can voraciously eat through foliage, stems, buds and flowers and do a lot of damage in a short time.

If you’re growing currants and berries, spuds or carrots, summer is time to keep a lookout for Currant Clearwing Moth, Raspberry Bud Moth, Potato Moth and Carrot Rust Fly.

Pernicious Passionvine Hoppers

Passionvine hoppers (Scolypopa australis) can cause damage to a very wide variety of edible and ornamental plants. Populations can skyrocket quickly and if left uncontrolled, can affect plant health, vigour and fruiting. Heavy infestations can potentially kill host plants.

Both adults and juveniles (nymphs) pierce the plant and suck out sugary phloem sap to feed. Excess sugars are excreted as sticky honeydew, so you'll often see opportunistic ants harvesting honeydew on infested plants. Adults and nymphs can be found at the tips of stems, often in large groups. When disturbed, they can jump away, which sometimes produces a loud snapping or clicking noise. Adults characteristically jump, then fly away when disturbed.

Eggs hatch in spring and nymphs emerge. Nymphs are sometimes called “fluffy bums”, due to the tuft of white fluff (filaments) attached to the tip of their abdomen. These long filaments can be fan-shaped and look a bit like a peacock’s tail.

Adults are most active from mid-summer to early winter.

Worsening Whitefly

Whiteflies resemble tiny white moths with a wingspan of 3mm. They've become very prevalent in recent years and tare major pests for home gardeners. Both the adult and juvenile (nymph) whiteflies feed by sucking the phloem sap from plants, causing a lot of damage in the process. Infestations of whitefly can drastically impede plant growth and reduce crop yields. They can cause wilting and stunting of new shoots, yellowing of leaves, uneven ripening of tomatoes and sometimes plant death.

Whitefly are easy to identify: if the plant host is disturbed, a distinctive 'flittering cloud' of tiny insects fly out, but they soon settle back onto the same plant.

Whitefly is challenging to control, as it goes through two life stages that are resistant to pesticides. This explains why a single spray won't always control it completely. A quick explanation of the whitefly life cycle will be helpful to understand why: adults lay eggs on young leaves, close to where they are feeding. When the eggs hatch out, they go through four different larval stages, that look like tiny scale insects, before forming a pupa, then emerging as an adult.

The big challenge is that the egg and pupal stages are very resistant to pesticides (although the adults and youngest nymphs are easily controlled). Because you can usually find all the different whitefly life stages on the same leaf at the same time, a single spray often won't kill them all, so the survivors can quickly mature and carry on feeding. When whitefly pest pressure is high, this can allow their population to recover before the next scheduled insecticide spray is due.

How to Stay Ahead of Whitefly

Whitefly is best controlled using two different insecticides and alternating them, in overlapping applications. Don't be tempted to shorten the spray intervals of any of our whitefly control products (always stick to the instructions) because whitefly can build up chemical resistance very quickly. Instead, if you alternate between different insecticides with different modes of action, this delivers the effect you're looking for.

For example, if you apply Yates Mavrik at the weekend, sticking to 1-week spray intervals, and then alternate with a mid-week dose of Yates Nature's Way Natrasoap Vegie Insect Spray at 1-week intervals, you'll be able to interrupt the whitefly life cycle and get complete control. Ensure you get complete spray coverage, including on the underside of leaves.

Maddening Mealybugs

Mealybugs are small flat-bodied insects, covered with a powdery-looking white coating; some have a fringe of white cottony threads attached to their bodies. They feed by sucking on plant sap, then excrete a sweet, sticky substance called honeydew which attracts ants. Honeydew also provides a perfect medium for sooty mould growth.

A persistent offender is the Longtailed Mealybug (Pseudococcus longispinus)

Mild temperatures and high humidity are perfect conditions for mealybugs to breed, as a new generation of eggs hatches every 2-3 weeks, from spring right through to autumn. Immature mealybugs prefer to hide in plant crevices or in the elbows between leaves and stems, so by the time you spot an adult the population can be bigger than you expect. Fortunately, prolonged hot weather helps to reduce numbers, so mealybug numbers peak in November and then decline over summer.

Calamitous Codling Moth / Obnoxious Oriental Fruit Moth

These caterpillars are a classic challenge for fruit tree growers. Unfortunately, summer is usually too late to prevent them. If the petals have already fallen from your tree, this season's grubs have already bored into your pipfruit; where they are effectively out of reach of insecticides.

Spring is the critical time to prevent Codling Moth or Oriental Fruit Moth spoiling fruit, as you need to apply Yates Success Ultra as soon as petals have fallen. Mark it in your calendar for next year - make this the last season you find half a grub in your apple! 

Accumulating Aphids

Aphids cause damage to plants directly through feeding, or indirectly as vectors of harmful viruses (which they inject into your plants in their saliva). They prefer to cluster on fresh young shoots and flower buds, or underneath older leaves.

There are 80+ different species of aphids in NZ; they all have different plant preferences, but between them they manage to attack fruit trees, citrus, roses, camellias and a wide range of vegetables. Here are some of the most commonly encountered pest aphids during summer:

• Black Citrus Aphids (Aphis citricidus) are glossy black or dark brown. You'll see them clustered in huge numbers on the growing tips of citrus trees in spring. These aphids are usually the culprits when leaf curl appears in citrus trees.
• Woolly apple aphid (Eriosoma lanigerum) have a preference for apple and pear trees; they cover themselves in a white fluffy woolly substance, which looks like clumps of cotton wool stuck to branches.
• Onion Aphids, AKA Black Aphids (Neotoxoptera formosana) are a serious pest of garlic, onions, chives, leeks and other alliums.
• The Cabbage Grey Aphid (Brevicoryne brassicae) is greyish-green, with a powdery-looking waxy coating. It feeds on all types of brassica crops, usually hiding on the underside of leaves.
• The Rose Aphid (Macrosiphum rosae) is common pest of roses. Green or pinkish coloured aphids can be seen swarming on flower buds and tender growing tips.

Troublesome Thrips

Thrips attack the flowers, fruit and foliage of vegetable crops and ornamental plants. They scrape the surface of the leaves and petals with their rasping mouthparts, then suck the sap out of the plant cells. The resulting damage leaves a distinctive silvery-white mottled appearance on leaves. Other symptoms are browning on petals and fruit, and flower drop. If left unchecked the leaves, new shoots and flowers will become deformed and stunted. Wilting and browning can also occur.

Thrips lay eggs inside plant tissue, where the hatched-out nymphs begin to feed on plant sap. Thrips also lay eggs inside unopened buds, which makes it difficult to control them with contact insecticides. Thrips larvae excrete a distinctive waste material called "frass", that looks like tiny black specks on infested leaves or flowers.

Thrips also spread plant viruses in their saliva while they feed; in NZ they are the cause of tomato spotted wilt virus (TSWV).

Malignant Mites

Mites are usually diagnosed by the damage they cause, because they aren't easy to see. Mites have piercing and sucking mouthparts which they spear into plant cells and suck out the fluid contents; this can have a drastic effect on plant health. Mites are most active in hot, dry weather, which allows them to complete their life cycle, from eggs to adults, inside a week. Mite populations can expand very rapidly when conditions suit them.

In NZ, the most challenging spider mites are the Two Spotted Mite (Tetranychus urticae, which attacks a wide range of vegetables, fruit trees and berries) and the European Red Mite (Panonychus ulmi, a serious pest of deciduous fruit trees and roses).

• Two spotted mites may be just visible as pale yellow-green mites with a couple of dark spots on the back, about half a millimetre long. In autumn, their colour changes to orange. They'll usually be clustered on the underside of leaves, plus they often spin fine webbing on leaves. Stippling, mottling or bronzing of leaves is common, progressing to leaves browning off and dying.
• European red mites are slightly smaller and pinkish-red in colour, but they don't leave visible webs - their damage often shows up first as tiny yellow specks on leaves, that spread out into pale bleached-looking or bronzed areas over the whole leaf.

Mites are often found on plants that are growing in dry situations (indoor plants and glasshouse-grown plants are especially vulnerable).

Catastrophic Caterpillars

Adult moths and butterflies are harmless to your plants and even do good service as pollinators. Unfortunately, their caterpillar larvae have chewing mouthparts and a voracious appetite, so even the smallest of caterpillars can eat through mountains of foliage; left unchecked they can skeletonise leaves and completely ruin flowers.

Regular monitoring of your garden means a major incursion won’t catch you unawares: caterpillar control methods are much more effective if you can tackle an infestation early.

The main vegetable pest caterpillars you’ll run into in summer are the Cabbage White Butterfly, Green Looper, Diamondback Moth, Leafrollers and Tomato Fruitworm.

If you prefer a natural control option, try Yates Nature’s Way Citrus, Vegie & Ornamental Insect Spray. It’s an organically certified pyrethrum and oil combination insecticide, with twin modes of action against garden pests. Made from natural pyrethrum (from the pyrethrum daisy) and canola oil, this formula effectively controls a wide range of insect pests, including caterpillars. It’s BioGro approved for organic gardening. Spray leaves thoroughly, including the undersides, as caterpillars often hide there.

Manual control methods can be very effective: placing fine insect netting over plants can prevent adult moths or butterflies laying eggs on your plants. You can also disrupt the caterpillar life cycle by pinching off leaves with eggs or small caterpillars on them, along with picking off and squishing large caterpillars.

Stealthy Scale

Scale insects drive their mouthparts into plant cells and suck out the contents, which eventually causes severe damage to the plant (which becomes much worse when the scale population gets high).

Adult scales form a protective shell and become immobile, locking themselves in place like limpets. Scale species can look quite different to one another: some species (known as soft scales or wax scales) exude waxy or fluffy-looking coatings, which can be white or pink in colour. Some species don't form any coating (these are known as hard scales) and are disguised better, as they look like raised brown or black bumps on leaves and stems.

Telltale symptoms of a scale infestation are ants speeding up and down plant stems (they're attracted to the sticky honeydew that scale excrete) and sooty mould, which grows on the honeydew residues.

Although most contact insecticides don't have any effect on scale because it's protected under a shell, it's easily controlled with regular sprays of Yates Conqueror Spraying Oil. Once the scale insects are gone and the source of the honeydew disappears, the ants and sooty mould will also depart.

Pestilential Pear and Cherry Slug

The Pear and Cherry Slug eats the leaves of pears, cherries, apples, plums, quinces and hawthorns. They actually aren't slugs at all; they are the larval form of a sawfly. As for sawflies, they aren't even flies! They're more closely related to wasps.

The glossy, slimy slug-like larvae are olive to dark black in colour and foul smelling (so wear gloves if you're manually squishing them).

The larvae feed on the inner leaf tissue, often leaving distinctive chewed-out 'windows', before skeletonising leaves completely.

Lurking Lemon Tree Borer

Lemon Tree Borer (also known as Citrus Tree Borer) is a very destructive native pest. Lemon Tree Borers favourite targets include lemons, apples, grape vines, walnuts, persimmons, and cherry trees. Lemon Tree Borer larvae tunnel their way along inside the centre of branches towards the stem. This prevents sap from flowing, and causes serious damage to the affected branch.

Warning symptoms of Lemon Tree Borer are wilting leaves or dieback of individual branches. Observation of 2-3mm round holes in branches, with visible clumps of powdery sawdust (actually, it’s borer poo that's thrown out by the larvae) confirms an infestation.

The adult beetles are flying at night through summer, on the lookout for trees to lay their eggs. The scent of freshly pruned citrus trees attracts them like a magnet, so it’s wise to put off pruning until April. A good solution for protecting fresh pruning cuts is Yates PruneTec, which seals off the wound and forms a physical barrier against larvae boring into the tree.

The old-fashioned control method is still best – get a wound guitar string or a length of thin wire, search for the borer holes and poke it in firmly as far as you can go. Simple, but effective.

Troublesome Tomato Fruitworm

Tomato Fruit Worms are caterpillars that chew holes into flower buds and fruit. They also chew patches out of developing leaves, causing plants to be stunted. They feed on a very wide range of host plants, so they can cause a lot of damage and defoliation when their population builds up.

Caterpillars range in colour from light green, to red, to almost black and often have light stripes along their back and sides. They pupate below ground to get through the winter, emerging as adult moths between November and March.

When feeding on tomato fruit, caterpillars usually hide under or around the stalks. The most obvious signs of an infestation are holes chewed by mature caterpillars into tomatoes, usually close to the calyx (the green starry shaped ruff around the stalk). Frass (caterpillar poo) is often visible near the feeding holes. Less obvious signs (when caterpillars are smaller) are leaf damage or defoliation, or tomato plants may be yellowed or stunted.

Exasperating Earwigs

Earwigs feed on a wide range of living and dead plants and even eat other garden pests, like aphids and caterpillars. Earwigs are attracted to soft new plant foliage and soft skinned fruits, so they can cause damage to vegetables (tomatoes, brassicas, cucurbits and leafy vegetables), fruit trees, citrus and indoor plants.

They feed at night, but during the day they'll be hiding in amongst plants, underneath rocks or debris, or concealed just under the soil surface. Once garden crops have finished, turn over the soil and leave it exposed so birds, lizards and skinks can feed on the earwig eggs and juveniles. Remove debris around the garden, like piles of timber and rocks, to reduce potential hiding and congregating sites.

Because earwigs are most active at night, it's best to spray in the early hours of the morning or at dusk.

Keep an eye open for these signs and symptoms of earwigs and tackle them early.

• Holes in seedling leaves or the tops of seedlings completely removed.
• Shredded or jagged edges, or irregular holes in leaves and flowers.
• Small jagged chewed holes in soft-skinned fruit.

Siphoning Psyllids

Psyllids are tiny sap-sucking insects that resemble miniature cicadas; you'll need a magnifying glass to see them properly. The main species of concern in spring is the tomato-potato psyllid (Bactericera cockerelli) also known as TPP, which has a special attraction to plants in the Solanaceae family, so tomatoes, potatoes, capsicum, eggplants, chillies, tamarillo and kumara are all affected.

Both juvenile (nymph) and adult stages damage plants by piercing and sucking sap from the leaves. They're especially attracted to weakened or unhealthy plants, so psyllid infestations can have devastating effects on stressed plant hosts. Unfortunately, tomato/potato psyllids also carry bacterial disease in their saliva, that can be injected into the plant while they feed (this is the primary cause of unsightly 'zebra chip' disease in potatoes).

A psyllid infestation can be hard to diagnose, because most of the symptoms are easy to mistake for other problems. Plants may become stunted, wilted, or develop yellow or purple upwards-curling leaves, often with purple leaf veins (the purple veins are a symptom of bacterial infection, which indicates psyllids may be the underlying cause). A more obvious symptom is a white sugary crystalline substance appearing on leaves; this is actually honeydew excreted by the psyllids (also known as 'psyllid sugar', it might be accompanied by sooty mould). If you disturb the plant foliage and see tiny insects springing out, they will probably be tomato-potato psyllids.

The most disappointing symptom of tomato-potato psyllid is getting tiny, inedible fruit at harvest time, for both tomatoes and potatoes.

Want a Short Cut?

Sometimes it’s hard to know exactly which insect is responsible for the damage – so it’s handy to have a do-it-all spray, that controls a really broad range of chewing and sucking insect pests.

Yates Nature’s Way Organic Citrus, Vegie & Ornamental Spray is our go-to organic control for aphids, mealybug, caterpillars, thrips, mites and whitefly. Keep it handy, so it's always ready to go as soon as you see pests! It contains a unique combination of pyrethrin (an extract from the pyrethrum daisy) and canola oil, to deliver two potent modes of action in a single spray. It's certified for use in organic gardening by BioGro NZ and registered for use on edible plants.