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Identifying Urban Garden Pests

Identifying Urban Garden Pests

Gardens are always full of bugs. Some are harmless, while others are on a mission to annihilate every last leaf, forcing gardeners to go into war-mode.

If you’re living in a city you might be less well acquainted our little six-legged friends, who can be difficult to identify. To help you out, we’ve compiled a list of some of the most common pests urban gardeners deal with. Find out how to identify them, what sort of problems they may cause, and what to do about them below.

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1. Aphids

Aphids in the urban garden

What:

Of all the urban garden pests, aphids are probably the most common. Aphids are tiny (1/8″ long), soft bodied, pear-shaped insects, that may be green, yellow, brown, red or black in color. Adults are generally wingless, but will occasionally grow wings in order to migrate to a new plant when the population on the current host grows too high.

Where:

In clusters, under leaves, and on tender new plant growth. These tiny sapsuckers can be found in both indoor and outdoor gardens.

Problems:

Aphids reproduce very quickly, which can lead to heavy infestations in a short period. Heavy infestations will cause leaves to curl, wilt or yellow and lead to stunted growth and a general decline in overall plant vigor.
 
Several species can transmit plant diseases, particularly viruses which they pass on during feeding.

Treatment:

  • Pinch or prune off heavily infested leaves or other plant parts.
  • Hose off plants with a strong stream of water to knock them off the plants.
  • Release ladybugs, a natural predator of aphids.
  • Spray with insecticidal soap or a food safe botanical insecticide to treat heavily infested areas. 
  • Avoid over watering or over fertilizing, as aphids like plants with high nitrogen levels and soft new growth. 

2. Earwigs

Earwigs in the urban garden

What:

Slender red-brown insects (3/4″ long) with elongated, flattened bodies and a pair of sharp pincers at the tail end.
 
Though earwigs might appear intimidating with their long pincers, they are not dangerous. They can use their pincers to grasp onto things (such as a finger) if agitated, but are not venomous. They get their name from the superstition that earwigs will crawl into a person’s ear and tunnel into the brain.  This superstition is, of course, untrue.

Where:

On or under the leaves, flowers and shoots of almost any outdoor vegetable, flower or ornamentals. However, earwigs are nocturnal, so you will likely not see much of them during the day. Instead, you will find them in the moist, dark areas of your garden such as under layers of mulch, or hanging around compost piles.

Problems:

Earwigs feed on plant shoots, foliage, flowers, and sometimes ripened fruit, causing damage or even plant death. Damage can be identified by ragged edges or holes chewed from leaves, petals, and fruit.

Treatment:

  • Remove debris and mulch from infested areas.
  • Place sticky traps
  • Spray with a food safe botanical insecticide

3. Leafminers

Leafminers in the urban garden

Image by Scot Nelson

What:

Adults (1/10″ long) are black or gray flies with yellow stripes and clear wings. The adult are not themselves the problem, though you may see them flying around amongst your plants.
 
What you need to look out for are the larvae. Larvae are worm-like maggots (1/3 inch) which are often pale yellow or green in color.

Where:

Leafminers tunnel between the upper and lower surfaces of leaves. Adults lay their eggs on the underside of leaves, and when the larvae hatch, they feed on the inner portion of the leaf leaving long squiggly trails as they go.

Problem:

These insects are not usually threatening to the survival of the plant as the damage they cause is mostly cosmetic. However, this can lead to reduced yields especially if the plant is heavily infested.
 
Of course, this is a bigger problem for lettuces, salad greens and other plants that are grown to produce leaves for consumption. Nobody wants larvae in their salad greens!

Treatment:

  • At the first sign of tunneling, squeeze the leaf at the tunnel between two fingers to crush any larvae. Done soon enough, this can help plants to survive minor outbreaks.
  • Pick off and destroy badly infested leaves in small gardens.
  • Neem oil will break the leafminer’s life-cycle by preventing larva from reaching maturity. It also acts as a repellent to keep away the egg-laying adults.

4. Slugs + Snails

Slugs and snails in the urban garden

What:

Snails and slugs are not actually insects — they’re members of the mollusk family. Snails have rounded swirly shells, while slugs do not.

Where:

In damp, shady locations feeding on live and decaying plant material. Snails and slugs are most active at night, but you can identify their presence by the shiny slime trails they leave on leaves and surfaces around your garden. They can be found on almost any garden vegetable, ornamentals, flowers, and some fruit trees.
 
If you’re up high on a balcony or rooftop, this is one pest you may get to dodge almost entirely. Those on the ground aren’t so lucky.

Problems:

Most active at night, snails and slugs chew large holes in foliage and can cause extensive damage to seedlings, and low-growing leafy vegetables, ornamentals and fruit. They are capable of killing large plants, and will eat your fruits and veggies before you are ready to harvest them.

Treatment:

  • Remove slugs from plants by hand.
  • Lay a copper tape barrier around susceptible plants. Slugs will not cross over copper.

5. Spider Mites

What:

An arachnid cousin of the spider, these mites are very tiny (1/50″) reddish brown or pale in color, and oval-shaped.

Where:

These sap suckers normally form colonies on the undersides of leaves, in both indoor and outdoor gardens.

Problems:

Spider mites pierce the leaves to feed, leaving tiny marks that show up as light dots. Eventually the leaves turn yellow, and may dry up and drop off. Plants with large infestations may be covered in fine silk webbing under the leaves and along the stems.

Treatment:

  • Careful containment and disposal of infested plants is crucial, as spider mites can use the wind to drift to new host plants.
  • Prune off leaves and other infested parts if the plant, then dispose of carefully.
  • Spray with a strong stream of water to  knock mites off the plant and reduce their numbers.
  • Introduce ladybugs, a natural predator of spider mites.
  • Spray with insecticidal soapneem oil, or a food safe botanical insecticide for heavily infested areas.

6. Whiteflies

Whiteflies in the urban garden

What:

Adult whiteflies are small moth-like insects with powdery white wings, approximately 1/16″ long. Nymphs are flat, oval, wingless and often very pale, making them hard to spot.

Where:

On the leaves, flowers and fruits of both indoor and outdoor plants, usually found near the top of the plant. This sap-sucking insect is often found in large numbers on the undersides of leaves. When disturbed, the winged adults will take to the air in a cloud of tiny white insects.

Problems:

Both nymphs and adults damage plants by sucking the juices from new growth. This can result in stunted growth, yellowing leaves and reduced yields. Infested plants become weaker and  more susceptible to disease as a result.

Treatment:

  • Place sticky traps near infested plants to trap adults.
  • Spray with a strong stream of water to reduce pest numbers.
  • Introduce ladybugs, a natural predator of whiteflies.
  • Spray with insecticidal soap, need oil, or a food safe botanical insecticide for heavily infested areas.

7. Thrips

What:

Thrips are very tiny (< 1/25″) yellow or black colored insects, slender with two pairs of transparent wings. Without the use of a magnifying glass, they resemble tiny dark threads.

Where:

On the leaves, fruits and flowers of many ornamental and vegetable plants, both indoor and outdoor. Thrips are very active and feed in large groups, and will jump or fly away when disturbed.

Problems:

Thrips damage plants by sucking their sap and scraping at leaves, flowers, and fruit. As a result, leaves may turn pale, splotchy, and silvery before dying. Plants that have been injured by thrip infestations are deformed and twisted, with discolorations and scarring.

Treatment:

  • Remove hiding places for thrips by getting rid of damp mulch and debris from around plants, especially if the debris is still green.
  • Place sticky traps near infested plants.
  • Spray with a strong  stream of water to reduce pest numbers.
  • Release ladybugs, which naturally prey on thrips.
  • Spray heavily infested areas with insecticidal soap, neem oil or other food safe botanical insecticide.

8. Tomato Hornworm

Tomato hornworm in the urban garden pests

What:

Hormworms are 3-4″ long caterpillars, the larval stage of the sphinx or hawk moth. These caterpillars are green with diagonal white strips along their body and a black or red horn projecting from the rear.
 
The adults are large heavy-bodied moths, with gray-brown coloring.  However, the adult stage moths are not considered pests, and are actually important pollinators in the garden.

Where:

Contrary to what their name implies, Tomato Hornworms do not solely infest tomato plants. They are one of the most destructive pests of not only tomatoes, but potatoes, peppers, and eggplants as well. Despite their large size, hornworms are often difficult to spot because their protective coloring helps them blend in with their surroundings.

Problems:

They consume entire leaves, small stems, and occasionally chew on fruit. One of the most destructive pests you can find in your garden, as they are both large and have voracious appetites.

Treatment:

  • Since they are so big, the easiest method is to remove them by hand. They can be killed afterwards by dropping them in a soapy water solution (if you are too squeamish to squish them).
  • If infestations are too heavy for hand picking, spot treat with an appropriate food safe botanical pesticide.

9. Mealy Bugs

Mealybugs in the urban garden pests

What:

Mealybugs are white, soft-bodied wingless insects that often appear in cottony looking masses on the leaves, stems and fruit of plants. They feed on the sap of various plant tissues. Adults  are 1/10″ – 1/4″ long, with oval shaped bodies that are usually covered with a white or gray mealy wax. Juveniles are light yellow and free of wax. They are active early on, but tend to stop move once they have found a suitable feeding site.

Where:

Found in warmer growing climates in outdoor gardens, and on indoor plants.

Problems:

Damage is not normally significant with only a few mealy bugs. However, in higher numbers they can cause leaves to yellow and curl as the plant is weakened. Feeding results in honeydew deposits on the surfaces of the plant, leaving it sticky as well as more susceptible to sooty mold growth.

Treatment:

  • Avoid over watering and over fertilizing, as mealybugs are attracted to plants with high nitrogen levels and soft growth.
  • Release ladybugs, a natural predator of mealybugs.
  • Spray with a strong stream of water to reduce pest numbers.
  • Spray plant regularly with neem oil to reduce the chances of future infestations.
  • Spray with insecticidal soap or another appropriate botanical insecticide.

10. Scale

Soft wax scale in the urban garden pests

Soft Wax Scale insects (and ants).

What:

Scale insets are oddly shaped shell-like bumps that are immobile and look more like a shell than an insect. Though there are two major types, there are many different species with vastly different appearances. The two major types are:
  • Armored – 1/8″ long and round in shape, these scale insects secrete a hard protective covering over their bodies. The hard scale feeds on the sap of the plant from under it’s protective layer and does not move. This type does not produce honeydew.
  • Soft –  Up to 1/2″ long, soft scale insects secrete a softer waxy film. They vary in shape in addition to size, and can range anywhere from flat to spherical. They are able to move short distances but normally stay in one place or general area. This type can produce large amounts of honeydew.

Where:

Attached to leaves, stems, and branches of many types of plants. Common on woody ornamental shrubs, trees, and house plants.

Problems:

Small infestations may go unnoticed, however large populations result in yellowed leaves, poor growth, and reduced vigor. If not treated, an infested plant can become very weak and eventually die.

Treatment:

  • Remove and dispose of infested branches, twigs and leaves.
  • If there is only a small number of scale insects, pick them off individually and dispose of them. Alternatively, dab the scale insects with a drop of neem oil or alcohol to kill them.
  • Introducing predatory insects such as ladybugs can help keep the infestation under control. However, since the predators can only feed on juveniles (adults are too well protected), they are not be beneficial in getting rid of adults.
  • With heavy infestations it is often best to dispose of the plant. Scale is notoriously difficult to eradicate completely (especially on plants with many small leaves and branches), and will spread throughout your garden if given the chance.

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