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Autumn brings change and transition to the garden. Warm summer weather might linger into March, but when cooler nights begin, the first frost won’t be far away.
For garden insect pests, the change of season is stark - you'll still encounter the more irritating summer pests during March, but they rapidly become less visible when cool weather arrives.
Aphids, white butterfly caterpillars and mealybugs are a different story. Their numbers peak in spring, decline through summer, but come surging back in autumn. Here’s a list of the pests to watch out for, this season.
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 autumn; they can voraciously eat through foliage, stems, buds and flowers and do a lot of damage in a short time.
If you’re growing spuds or carrots, keep a lookout for Potato Moth and Carrot Rust Fly.
The main vegetable pest caterpillars you’ll encounter during autumn are the Cabbage White Butterfly and Diamondback Moth. Green Looper caterpillars will disappear in early autumn.
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.
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.
The Mealybug population peaks in autumn, then again in spring. April is their most active month during autumn.
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)
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.
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 autumn:
Whitefly numbers reach a peak in March and decline rapidly as cooler weather arrives. They've become very prevalent in recent years and are major pests for home gardeners. 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 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.
The green vegetable bug (AKA shield bug, or stink bug) is mostly active in warm weather, during summer and autumn (but it does overwinter, so adults can be spotted throughout the year). They love to feed on beans, tomatoes, potatoes, sweetcorn and grapes. It's challenging to control, because while the solutions below will kill green vegetable bugs on contact, they won't prevent unsprayed bugs arriving from elsewhere and continuing to infest your plants.
The green vegetable bug sucks the sap from stalks and leaves and the juices from fruit. If disturbed (or squashed) this pest emits an unpleasant chemical with a strong odour, which can stain fingers and clothes, so be sure to wear gloves if you are manually removing bugs. Manual squashing is quite effective, as the odour seems to discourage new bugs from entering the area.
Classic symptoms include wilting plant shoots, from sap loss; fruit can become distorted and misshapen, especially beans. Hard corky growths can appear around where the bugs have pierced the plant to feed.
Snails and slugs can devour young seedlings overnight, or slime their way in amongst the leaves of the developing cabbage or lettuce heads. These pests are most active on cool, wet and humid nights, so they're at their worst during autumn (and spring), reaching peak numbers in April. They eat decaying animal matter and algae, but they're also delighted if they can find delicious vegetables to eat!
To prevent damage to your vegies, lightly scatter some Yates Blitzem Snail Slug Pellets around the plants.
Carrot Rust Fly is a serious pest of carrots in the warmer parts of the country. This fly also has a liking for parsnips, celery and parsley. Carrot Rust Fly populations are at their highest during autumn, but slow down in winter.
Adult flies locate their target crops using scent, then lay their eggs in the soil around the crops. The maggots burrow into the carrots to feed, causing deep, unsightly tunnels or channels circling the outside of roots, filled with rusty-looking mush. This damage often allows an entry point for bacterial rots to get started, which spoils the entire root for eating.
First symptoms to watch out for are yellowed and discoloured leaves, wilting or a generally stunted appearance to carrot tops.
Physical barriers like fine garden mesh or windbreak cloth placed around your carrots prevent the adult flies from laying eggs near them. Make certain there aren’t any little gaps, as the flies can smell their way to your crops!
Psyllids are tiny sap-sucking insects that resemble miniature cicadas; you'll need a magnifying glass to see them properly.
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 psyllids.
Tomato Fruit Worm chews 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. The good news is that their population starts to decline as autumn arrives, although they do continue through autumn at low levels.
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.
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 prefer hot, dry weather, which means you'll only see them in early autumn.
In autumn, mite pests are likely to be the Two Spotted Mite (Tetranychus urticae, which attacks a wide range of vegetables, fruit trees and berries).
If you look carefully, they may be visible as orange mites with a couple of dark spots on the back, about half a millimetre long. 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.
Mites are often found on plants that are growing in dry situations (indoor plants and glasshouse-grown plants are especially vulnerable).
The Pear and Cherry Slug eats the leaves of pears, cherries, apples, plums, quinces and hawthorns. Their numbers peak in early autumn; they are generally gone by mid-autumn.
Oddly, they aren't slugs at all; they are the larval form of a sawfly. As for sawflies, they're not 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.
Thrips attack the flowers, fruit and foliage of vegetable crops and ornamental plants. Thrips are generally summer pests, so you can expect them to be gone by mid-autumn.
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. Thrips larvae excrete a distinctive waste material called "frass", that looks like tiny black specks on infested leaves or flowers.
Earwigs feed on a wide range of living and dead plants and even eat other garden pests, like aphids and caterpillars. They're attracted to soft new plant foliage and soft skinned fruits, so they can continue to cause annoyance during March, before numbers drop off with cooler weather.
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. When your summer 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.
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). Fortunately, scale numbers peak in early autumn, then tail off rapidly as colder weather arrives.
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. As an example, you might see Cottony Cushion Scale on ornamentals during autumn.
Some species don't form a soft coating (these are known as hard scales) so they're disguised better. They look like raised brown or black bumps on leaves and stems. You'll see San Jose Scale on deciduous fruit trees, citrus, berry canes and ornamentals in early autumn, but numbers decline sharply before winter arrives.
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.
During the pipfruit harvest, these pests are front of mind for fruit tree growers. It's no fun finding rotten mushy tunnels inside your apple!
Unfortunately, there isn't any way to fix this season's damaged apples; the nasty caterpillars bored into your pipfruit back in spring; they've been worming their way through your fruit ever since then.
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 - and make the next harvest grub-free.
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.
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