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Tree and Shrub Pests and Diseases

With our fertile climate and soils in Memphis and the Mid-South, insects and pests will multiply if they go unchecked.  Close inspection and preventative measures are critical for healthy, thriving shrubs. What follows are the main enemies of shrubs in the Memphis area.

Get Rid of Tree and Shrub Pests and Diseases

The ornamentals in your yard are typically hardy plants. With proper care, they can live for generations and become centerpieces of a local community. However, this doesn’t mean that they’re invulnerable to diseases and pests, many of which are capable of causing real trouble. Knowing what to look for is key to stopping pests and diseases from getting out of hand, so let’s meet a few of the usual suspects.

Tree and Shrub Pests

Unsurprisingly, a healthy yard attracts all sorts of insects. Unfortunately, though, many species of insects have less than friendly intentions when they come onto your property. A few common yard pests include:

Aphids

One of the most common pests in yards and gardens all over America is the rose aphid, often referred to as Greenflies or simply Aphids. 

Appearance

These small, green, soft-bodied insects are often found in large colonies, particularly in early spring, where they suck the sap from young plant stems. 

Prevention

Aphids can be controlled by simply washing stems with water or spraying with an insecticide containing acephate or malathion. Nature also provides a defense against aphids in the form of Ladybugs, who can eat up to 50 aphids a day! Cultivating herbs and heavily-scented flowers in your yard can naturally attract Ladybugs.

Bag Worms

Bag worms are caterpillars that make distinctive spindle-shaped cocoons on a variety of trees and shrubs. They target both deciduous trees and evergreens but are especially attracted to juniper, arborvitae, spruce, pine, and cedar. Large populations of bag worms can quickly strip plants of their foliage, eventually causing them to die. 

Appearance

Bag worm infestations often go unnoticed because people mistake the protective bags for pine cones or other plant structures. 

Prevention

During the early stages of a bag worm infestation, usually in fall or winter, picking the cocoons off by hand may be effective. For more serious infestations, professional help is required. 

Japanese Beetles

Japanese Beetles are some of the most common and voracious garden pests that you’ll ever encounter. 

Appearance

A subspecies of the fabled Scarab Beetle, these invasive pests are easily identified by their metallic green and bronze bodies and robust black legs. Japanese Beetles aren’t picky. They’ll eat more or less any plant they can find and can make quick work of an entire garden if left unchecked. 

Prevention

Insecticides are effective at controlling Japanese Beetle populations but preventative maintenance is just as important. Typically, this involves removing the beetles from plants by hand. Applying mesh covers to your plants between May and August has also been shown to be effective.

Lace Bugs

Lace Bugs live on the lower leaf surface where they feed on a plant’s liquids through slender, piercing mouthparts. This leaves numerous yellow or white spots on the upper leaf surface. As the insects feed, they deposit their hard, black, varnish-like excrement on the leaf, which is commonly referred to as “tar spots.”

Reproduction

Lace bugs can have several rounds of young during a season if the host plant supports them. When their numbers become high and their feeding finally depletes the plant its leaves will turn brown and drop. 

Prevention

To manage lace bugs, periodically inspect plants that have been attacked in the past or are known hosts of lace bugs, and treat as soon as an infestation is apparent. Plants under stress are more susceptible to severe infestations, so evaluate the site and culture for infested plants. 

Scale Insects

Scale insects refer to a wide variety of insect species that cling to plant stems or tree bark in large numbers and feed off their sap. Affected areas appear scaly due to the insect's tendency to feed close together and can be sticky to the touch. The excess sap in these areas also provides ideal growing conditions for sooty black mold.

Prevention

Scale insects can be controlled by insecticides and by carefully pruning and disposing of affected areas. Scale insect infestations can grow beyond control quickly, when you notice them in your yard, swift action makes all the difference.

Spider Mites

Spider mites live in large colonies underneath leaves, giving off the appearance of white and black flecks similar to salt and pepper. As mite numbers increase, white specks will increase in number and the affected leaf will take on a bleached appearance and die.

Prevention

If the problem is detected early enough, you can control it with EPA-approved insecticides applied directly to the underside of the leaves. If you prefer, apply a fine misting of water to the undersides of the foliage to wash the mites to ground level; they are unable to fly, so they will die on the soil surface.

Whiteflies

Whiteflies feed on plant sap and, due to their large numbers, they’re capable of causing severe damage to an affected plant. Similar to scale insects, the side effects of their feeding can lead to mold growth, on top of the damage caused directly by their feeding.

Appearance

Whiteflies are small winged insects, closely resembling small moths. Their body produces a powdery wax which provides them with protection but is also key to identifying them. They thrive year-round in the South but go dormant during the winter in northern states. 

Prevention

Spraying water onto affected plants can dislodge whiteflies but insecticides are effective at treating a severe infestation. 

Wood Borers

Wood borers is a catch-all term for any different species of beetle whose larvae mature in tree trunks, just underneath the bark. Sometimes wood-boring beetles can even be found in the wood furniture in your home!

Common Species

Common wood borer species include:

  • Emerald Ash Borer
  • Asian Long-Horned Beetle 
  • Common Furniture Beetle

As the larvae mature, they eat the surrounding wood, which can cause severe damage, even to mature trees.

Prevention

Fast-acting insecticides and injectable chemical treatments are effective at treating tree-born wood borers but, for home infestations, heat treatments are typically recommended. 

Tree and Shrub Disease and Fungus

Particularly in the South, trees and shrubs are susceptible to disease and fungus. Anywhere with humid conditions provides ideal growing conditions for many different fungi and disease varieties but ornamentals in all growing conditions can still be vulnerable. Some of the most common yard fungi and diseases in Tennessee include:

Iron Chlorosis

On plants infected with Iron Chlorosis, leaves may become yellow, cream-colored, or white. This is usually caused by reduced availability of iron in high pH soil. Fortunately, this can be corrected by site-related treatments such as balancing soil pH and aerating solid to reduce waterlogging. Iron chelate applied to foliage may provide temporary greening, but for long term control, lowering soil pH and increasing oxygen in the soil are the best solutions. 

Leaf Scorch 

Leaf Scorch is a symptom that can occur when leaves experience water shortages. It may also be caused by diseases of the roots, crown, and vascular system, high ambient temperatures; damage to the roots from transplanting, soil compaction, natural gas leaks, chemical damage from herbicides, excessive fertilizing, or road salt. To avoid leaf scorch, be sure the soil is moist in the fall and to perform regular watering in the summer months. Additionally, provide windbreaks around plants and plant locally adapted varieties in sheltered locations.

Black Sooty Mold

Black Sooty Mold is a darkly-colored, powdery fungus that can easily grow around insect damage to plant stems or leaves. The presence of this mold can be directly related to a scale insect or whitefly infestation. Spraying affected plants with insecticides can loosen the mold and kill any insects whose feeding helps enable its growth. This can be particularly effective when done before a heavy rainfall when loosened mold can be washed away. 

Black Spot

Black spot is one of the most common fungi that affects all members of the rose family, including apple and pear trees. Outside of the rose family, any plant with fleshy leaves can also be affected. The infection itself is not hugely detrimental to the plant’s health but can weaken its leaves overtime which lessens its ability to photosynthesize and can make it more vulnerable to other damage. Both fungicide and diligent pruning are effective control methods against black spot.

Blight

Rather than a specific infection, blight refers to a series of symptoms that can affect many different plant varieties. These symptoms typically result in the death of soft plant tissues and can be easily spread from plant to plant through incidental contact. Unfortunately, the most effective means of blight control involves the careful removal and disposal of infected plants. This should be carried out by a trained professional as blight can be easily transmitted between plants on clothes or skin. 

Cankers

Cankers are diseased areas of the bark caused by different kinds of fungi and bacteria. The outer bark may appear abnormal while the inner layer of bark becomes discolored. In time, the bark may fall off, exposing the tree to further damage from insects. Leaves beyond the canker may also yellow, scorch, or die. Usually, canker-causing pathogens can infect only hosts that have been injured or stressed. Management of canker disease includes avoiding unnecessary injuries and pruning diseased branches well below the visible infection. After each cut, disinfect pruning tools with rubbing alcohol or 10 percent household chlorine bleach in water. With Rhizoctonia/Phoma canker or “die back,” stems and leaves may become blackened or blighted and shoot beyond the necrotic area wilt and die. It may also be necessary to increase air circulation by pruning overhanging shrubs and improve drainage by amending soil.

Gall

Galls are tumor-like growths visible on plants and can be caused by a wide variety of insects, diseases, or fungi. As with any condition caused by such a large variety of infections or infestations, it’s difficult to isolate one method of treatment or prevention and professionals typically approach galls on a case-by-case basis. Still, there are steps you can take to avoid galls on your plants such as using tree wrap in the winter and regularly cleaning garden tools. When galls do appear, carefully prune away and dispose of the affected areas and clean your tools before using them on another plant. 

Powdery Mildew

Powdery Mildew is a very common fungal infection that affects a wide variety of plants, but is particularly common on vegetables that grow close to the ground like squash or cucumbers, although mildew-resistant varieties of these are widely available. Staging plants in sunny areas is an effective means to stopping powdery mildew spread as it prefers shady conditions and heavy, overhead watering can help rinse spores off of leaves as a preventative measure. Fungicides are effective at treating powdery mildew and are among the surest methods at keeping it under control. 

Root and Crown Rot

Root rot is usually caused by any number of fungal infections that occur in and around overwatered plants and can often result in the death of the affected plant. The best way to control root rot is to avoid it in the first place. This can be accomplished by watering responsibly, according to the plant’s specific needs and by aertating your soul to allow for greater oxygen uptake. When root rot does occur, replanting the affected plant after trimming damaged root sections with sterilized scissors can be effective. 

Scab

Scabs can occur on most plant varieties and are caused by fungal infections, most of which occur in wet or humid conditions and are spread through either soil or infected seeds. Infected leaves and fruits develop lesions and can become dull in color. Fortunately, it is usually not a serious threat to the plant’s health and can be easily treated by fungicides. 

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