Texas encounters its fair share of challenges, and to keep your landscape looking its best, we’ve outlined some of the common pests and diseases that your trees and shrubs may encounter. Being aware of the threats against your plants will prepare you to fight off the challenges and keep your landscape looking as beautiful as ever!
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Common Pests of Trees & Shrubs
Leafhoppers are little, plant-eating insects that will feast on your trees and shrubs. They lay their eggs in the leaf veins, shoots, and stems of your plants. The eggs hatch within 10 days and nymphs will begin feeding on the new growth of the host plant. These pests will go through five stages in their lifetime, typically producing one generation each year but can reach up to six!
Adult leafhoppers will usually jump when disturbed, making them easier to spot. Nymphs and adults will also crawl away and hide if bothered. You can find leafhoppers feeding on the undersides of leaves and discover their molted cast skins attached to the lower leaf surfaces.
Besides eating away at the growth of your trees and shrubs, leafhoppers may also transmit diseases and cause injury. Feeding can lead to Hopperburn. Hopperburn is the development of marginal chlorosis and necrosis, or discolored spots on leaves, resulting in foliage curling.
To decrease the number of leafhoppers on your plants, integrate a biological form of control such as introducing lady beetles which will consume the leafhoppers! For cultural control, hand prune the damaged areas to encourage new growth and restore plant beauty.
Bagworms create and live in a transportable encasement made from leaf particles, twigs, and bark. They attach these protective bags to the plant, feeding on and destroying plant material. The feasting habits of bagworms can be very damaging for your plants, causing injury and plant death due to defoliation.
Males are the only bagworms to fully emerge as moths from their case after the egg, larvae, and pupae stages. Wingless females will partially emerge for mating purposes, but once eggs are produced, she will die and fall from her bag. Females may produce 400-1,000 eggs, laying them within her bag to develop.
When infestations reach larger amounts, an effective solution is to handpick the bagworms from your plants. As you collect, place the bagworms in a sealable bag to be discarded. You want to eliminate the chances of bagworms returning, so watch out for fallen cases that could hatch more eggs later and repeat the infestation!
Lace Bug
Lace bugs are easily identifiable by their lace-like wings and rectangular body shape. They feast on both trees and shrubs. These insects will lay their eggs on the undersides of leaves, producing three to five generations a year.
Lace bugs will infest plants, feeding mainly on the undersides of leaves. Evidence of damage can be seen by the dark spots and the shed skins from previous growth stages. The damage is noticeable on the tops of leaves as well, where there is chlorotic and necrotic (white, yellow, and brown) discoloration. In serious cases of infestation, your plants may even experience plant stress or die!
Unfortunately, where leaves are discolored from lace bug feeding, there is no return to normal health. These leaves will need to be pruned so the plant can produce new growth. Keep your plants healthy by providing proper irrigation and care. You can introduce a natural predator like lady beetles for biological control.
Spider mites are evasive creatures closely related to spiders and ticks with eight legs. Spider mite infestations commonly peak during July until September, when the weather is dry and hot. You will find these little invaders on the undersides of leaves. Because they are so small, the easiest way to spot them is to shake a leaf over a white piece of paper where the spider mites will fall and become visible.
Your plants will suffer from spider mite infestations resulting in stippled leaves with yellow, gray, or brown spots. This is why it’s important to keep an eye on your plants since early spider mite detection will result in fast recovery.
If you are able to catch an infestation early, eliminate the spider mites by spraying the undersides of leaves weekly with high pressured water. Encourage good plant health by watering and regular care. A natural spider mite predator to introduce are lady beetles, which will eat and eliminate these pests.
Aphids are tiny insects that can reproduce with or without a mate. Aphid infestations are rapid since they reproduce faster than any other insect. Aphids come in all kinds of shapes and colors, making them difficult to identify. Some types of aphids also have wings, developed from changes in their environment.
Aphids cause damage to your shrubs by sucking plant sap with their piercing and sucking mouthparts.These insects may feed on all parts of your plants, even injecting toxic salivary secretions into the plant that causes even more damage. Damages include:
- Stunted plant growth
- Deformed foliage
- Discolored leaves
- Galls formed on leaves, stems, and roots
- Sooty Mold fungus
- Transmitted plant viruses
To control aphid infestations, keep a close eye on your plants, inspecting them for any signs of aphids. You can find aphids anywhere on a shrub, but they commonly hang out on the undersides of leaves. You may introduce natural predators of aphids like lady beetles, which will effectively knock down the population of aphids. Spraying plants with high pressured water will knock aphids off leaves.
Whiteflies are little, wax-covered pests that feed on and damage your shrubs. Whiteflies can travel longer distances by flying in air currents. They lay their eggs on the undersides of leaves and females will produce 150-300 eggs in their lifetime.
To prevent a whitefly infestation, be sure to monitor your plants frequently for early detection. Avoid overwatering and excessive fertilization as this invites whiteflies. To reduce the populations of whiteflies and also eliminate honeydew and sooty mold, spray the undersides of leaves with high pressured water. Ladybeetles are just one of the many natural predators of whiteflies that will knock down the population!
Often mistaken as part of the plant, scale insects will sit on shrub leaves and feed. Adult scale insects will not move, so they are often presumed to be fungal growths. They damage plants by sucking the plant’s fluids, causing discoloration and leaf drop as well as plant decline or death. They also excrete honeydew which attracts sooty mold fungus.
You can control smaller infestations by simply knocking off all the scale. For more severe infestations, prune away areas where growth is damaged. Plant replacement may be necessary for severe infestations.
Leafspot is a disease that affects the foliage of ornamentals and shade trees. The fungi and bacteria that can cause this disease flourishes when the foliage remains wet for extended periods of time, conditions where the temperatures are 50-90 degrees, during heavy rain seasons, or in areas with poor drainage. Giving your trees too much water invites this disease!
Symptoms of leafspot include black dots within the spot, rings, or central cluster and spots conforming together to create blotches. Some insects can cause damage similar in appearance to leafspot disease! Watch out for new leaves or shoots that collapse quickly or have a slimy, dark appearance.
To help plants recover from leafspot, remove any affected leaves at the time of first noticeable symptoms. Clean your pruning tools with rubbing alcohol to prevent the spread of disease to other plants. Drip irrigation is a great way to ensure proper watering while keeping the plant foliage dry.
Powdery mildew is a fungal disease that appears on both trees and shrubs. It has the presence of a light gray or whitish powder that coats the leaf’s surface. Conditions that may encourage this disease include low soil moisture paired with high humidity levels at the plant surface and warmer days or cool nights during the spring and fall.
The beginning of powdery mildew disease starts as raised, blister-like areas on younger leaves. This causes the foliage to curl and expose the lower leaf surface. There is a narrow range of hosts that each species of powdery mildew will attack, however, there are 11,000 species of powdery mildew fungi where ornamentals are hosts. Powdery mildew disease will primarily attack young, succulent growth as mature leaves are not commonly affected.
To help your plants fight powdery mildew disease, you can prune and stake your plants. This will improve air circulation. Before pruning your trees or shrubs, be sure to disinfect your tools with rubbing alcohol. If there is infected foliage, you can simply remove these leaves. To help prevent the disease spores from splashing back up onto the leaves, place a thick layer of mulch over the soil. Drip irrigation or a soaker hose will deliver the proper amount of water while keeping the foliage dry.
Sooty mold disease is difficult because once it established, it is very hard to remove. This disease is a frequent challenge with deciduous trees and shrubs including:
- Crepe myrtles
- Chinese elms
- Hollies
- Silver maples
- Sugar berries
- Plants that grow beneath any of the above plants
Sooty mold typically grows on insect excrement, also called honeydew. It coats the leaves, stems, and fruit of your plants. Although the mold isn’t parasitic, it can diminish the photosynthetic ability of leaves by obstructing light. Sooty mold is a good sign that your plant is infested with insects including aphids, scale, mealybugs, or whiteflies
The best solution for sooty mold is to solve the insect problem. This will stop the sugar deposits and the mold will eventually go away. Water-splashed spores or air-borne spores may transport fungi from plant to plant.