Bugs: Good and Bad

All gardens have some munched-on leaves and insect galls, but how can you tell if it’s really a problem?

Use our guide below to identify the problem and find out what to do if your plants start looking stressed.

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Insects damage plants during their feeding activities. Some insects, such as beetles, grasshoppers, or caterpillars, create chewing patterns in leaves and flowers, while other like aphids or scales cause leaves to shrivel up or turn yellow as they suck sap.  A little bit of damage from insects is to be expected and not a concern because plants are able to withstand it. However, if your favorite plants are beginning to look ragged or sickly, try the measures below to help reduce the problem.

CATERPILLAR MANAGEMENT

What’s Happening

Caterpillars are particularly active in the early spring when vegetation is new. Fortunately, many spring caterpillars become excellent food for hungry baby birds or other insects. Caterpillars become gorgeous butterflies or unobtrusive moths.

Threat Level

Mild. Consider letting the infestation run its course. Native trees and other well-adapted plants will not suffer long-term harm from these infestations.

TREATMENT CATEGORY EFFECTIVENESS NOTES
Strong Spray of Water Mechanical Control Fair A strong spray of water will dislodge caterpillar eggs and the caterpillars themselves off your treasured plant. This gives the birds and other predators a chance to catch up with the population and keep them down to reasonable numbers.
Bacillus Thurengiensis (Bt) Biological (Bacterial Extract) High Bt works by disrupting the digestive systems of caterpillars. It does not negatively impact other insects or wildlife. However, it must be applied regularly so that it is eaten by the caterpillars. It will wash off in rain and degrade in sunlight. Use caution because Bt affects both moth and butterfly caterpillars.
Insect-Killing Soap Chemical (Organic Control) Fair Insect-killing soaps that act on both target pests and beneficial insects. The soap kills on contact by disrupting the insects’ outer protective layers. It does not harm other wildlife. It must be reapplied often.
Spinosad Chemical
(Organic Control)
High Spinosad is a natural fungus that kills on contact and works very well on insects that chew leaves.
APHIDS

What’s Happening

Aphids are easy to spot if you have identified them once. They are only 1/16 to 1/8 of an inch in size. At first glance, they appear to be tiny bumps often found all over new flower buds or on newly-sprouted plants.

They reproduce very quickly and feed by sucking sap from plants. Aphids leave behind a sticky “honeydew” composed of undigested sap and water. Sometimes ants protect them from predators in order to harvest the honeydew to feed their larvae and other ants.

Threat Level

Mild. Aphids are annoying, but rarely fatal. Natural predators will often catch up with them and if natural numbers are low, predators can be purchased online to release. Help the process along with some of the steps listed below if they seem to be overwhelming a favorite plant.

TREATMENT CATEGORY EFFECTIVENESS NOTES
Strong Spray of Water Mechanical Control High A strong spray of water all around the buds and other badly-infested areas. This will dislodge the aphids and is equally effective to most insecticides. Most effective if repeated every two days.
Predators such as Ladybugs Biological Control Fair, but give time for ladybugs to find the aphids. It is possible to buy ladybugs and other predatory insects at local nurseries or online. There is no harm in releasing them in your garden. The easiest method is to allow small infestations to attract naturally-occurring predators.
Insect-Killing Soap Chemical (Organic Control) Fair These act on many soft-bodied insect pests and on beneficial insects. The soap harms insects by disrupting their outer protective layers. It does not harm other wildlife and needs to be reapplied often.
Oils such as Neem and Canola Chemical
(Organic Control)
Fair Spray directly on affected areas to suffocate insect pests in their early stages. Neem and Canola also have insecticidal properties. Follow label instructions to prevent injury to tender ornamental plants.
Pyrethrum Products Chemical
(Organic Control)
High Pyrethrum is derived from chrysanthemum plants. Organic does not mean safe. They are harmful to honey bees though short-lived. They may be combined with other insecticides to counteract natural defenses of insects. Pyrethrins are non-organic cousins that are synthetically enhanced to have higher toxicity to insects and more stability in sunlight for longer impact.
SNAILS AND SLUGS

What’s Happening

The slimy trails left by these two pests are their hallmark. They can generally be discouraged through the use of baits, or physically removing them at night when they are active.

Threat Level

Serious on non-native plants. Snails and slugs are not usually a problem on native or well-adapted plants. However, they will destroy tender and well-watered annuals like pansies or annual seedlings. If you see them getting started, control them with the steps below.

TREATMENT CATEGORY EFFECTIVENESS NOTES
Beer or Other Traps Mechanical Control Excellent Place small containers of beer or apple cider near affected plants. Slugs and snails fall into traps.
Copper Barrier Tape Mechanical Control Mixed results; May discourage attacks Use copper stripping around planters to prevent slugs and snails from getting to non-native plants.
SPIDER MITES

What’s Happening

Tiny spider mites thrive on heat and dry weather. This makes them a problem during San Antonio summers. The symptoms include leaves that turn brown and curl under with many yellow specks. There may also be a fine webbing under leaves.

Threat Level

Serious if you see damage. You should not expect to eliminate spider mites, but to discourage them from overwhelming plants. A healthy native or well-adapted plant will rarely show any signs of spider mite stress. Try the steps below early when they start to appear.

TREATMENT CATEGORY EFFECTIVENESS NOTES
Strong Spray of Water Mechanical Control Fair A strong spray of water of water directed on underside of leaves every two days keeps spider mites from getting out of hand.
Insecticidal Soaps & Horticultural Oils Chemical
(Organic Control)
Fair Spray these products up at leaves from underneath for maximum effectiveness.
Foliar Seaweed Spray Chemical
(Organic Control)
Fair Foliar seaweed spray provides nutrients to plants and is a tool used by Master Gardeners and others to reduce spider mite infestations on plants.
Natural Predators; Lacewing Larvae and Predacious Mites Biological Fair If you avoid overuse of broad-spectrum insecticides, you will have some natural predators to help control spider mites.
Removal of Badly Infested Plant Material Cultural Practice Fair If a plant seems overrun with spider mites, consider removing the plant. Established perennials will grow back after infested growth is removed.
GALLS

What’s Happening

Galls are formed by insect or fungus using leaves as hosts. Leaves with galls sometimes look deformed, but will still have good color and vigor. Galls don’t cause any long-term harm to plants. No treatment is recommended.

Threat Level

None. The galls do not cause any long term harm.

SCALE INSECTS

What’s Happening

These are tiny, sucking insects that are most often found on the underside of leaves. They can look like natural bumps and do not seem to move.

Threat Level

Low for native or well-adapted plants. High for houseplants or tropicals.

TREATMENT CATEGORY EFFECTIVENESS NOTES
Remove Affected Part of Plant Early in Infestation Mechanical Fair Consider discarding highly-infested individual plants from garden. Prune badly-infested parts of larger plants and discard in trash.
Dormant Oil Chemical (Organic Control) High Dormant oil can be used during winter months only. It helps to suffocate scale insects.
Horticultural Oils; Canola and Neem Chemical (Organic Control) High Spray directly on affected areas to suffocate insect pests in their early stages. Neem and Canola also have insecticidal properties. Follow label instructions to prevent injury to tender ornamental plants.

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