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Problematic Shrub Diseases

Unfortunately, landscape shrubs are prone to problems with numerous diseases. If your plants show signs of an infection, it’s best to quickly determine the problem and take the appropriate course of action.

The following are some of the most common diseases in shrubs.

Phytophthora Root Rot

Phytophthora root rot is one of the most problematic shrub diseases caused by the soil-borne fungus Phytophthora parasitica. Plants are commonly infected in the spring and fall when cool and wet. After the roots become infected, the fungus causes them to rot, stopping the plant from taking in water and nutrients. The shrub appears to be wilting even though it has plenty of water.

Boxwood Blight

Boxwood blight is a relatively new disease caused by the pathogenic fungus Calonectria pseudonaviculata. The disease infects boxwood shrubs and other members of the same family. It is common in humid climates and spreads aggressively when shrubs are planted close together.

Symptoms appear as tan circles on leaves with dark brown borders, black stems or stem lesions, and rapid leaf drop.

Anthracnose

Anthracnose is a term used to loosely classify a group of related fungal diseases that cause dark lesions on the leaves or irregular brown patches along the veins. In the spring, the fungus spreads from infected tissue to new growth.

Powdery Mildew

Powdery mildew frequently occurs on plants, but it is one of the least harmful diseases. You can quickly identify it by its white or light gray powdery coating on the leaves. It is caused by a fungal pathogen and may cause leaves to become distorted.

Canker

Canker diseases occur when an open wound on the shrub’s bark becomes infected with a fungus or bacterial pathogen. The inner bark layer usually becomes discolored, and the bark may fall off over time. Leaves past the canker may yellow or die. Once under the stem, canker diseases typically kill branches or structurally weaken them until the infected area breaks off in an ice or wind storm.

Sooty Mold

This type of disease typically goes hand-in-hand with sap-sucking insects. Several species of fungi and molds use the honeydew secreted by these bugs as a food source, so they develop and grow. Sooty mold usually does not damage the shrub but is a nuisance and eyesore.

Rust

Rust is the common name for a group of fungal diseases infecting shrubs, causing masses of reddish, orange, or yellowish powdery leaf spots. Infection typically deforms leaves, and severe infection may cause branch dieback that occasionally kills the shrub.

Wilt

Fusarium and Verticillium wilt are shrubs’ two most common types of wilt diseases. Once infected, the leaves and stems wilt. Leaf margins may turn yellow and begin to curl upward before dropping.

Both types of wilt are caused by fungi that live in the tiny tubes (xylem) that carry water through the shrub’s vascular system. The fungus prevents water transport through the xylem, causing the plant to wilt.

Fungal Leaf Spots

Different fungus types cause different types of leaf-spot diseases in shrubs. All the disorders show up as tiny reddish-brown spots on the leaves that darken and dry out as the leaves mature. The infecting fungal spores overwinter on fallen leaves and spread through splashing raindrops to healthy tissue.

How to Treat Common Shrub Diseases

The first step is identifying the disease and determining if it is treatable. You cannot treat diseases like Phytophthora root rot and Fusarium wilt, so the shrub and surrounding soil need to be pulled out and discarded.

If the disease is treatable:

Remove all parts of the shrub that are showing signs of infection.
Prune the center of the shrub to improve air circulation.
Water the soil around the base of the shrub instead of watering from overhead to keep water off the foliage.
Hold off on fertilizing plants until they are healthy again.
Treat with appropriate fungicide or bacteriacide, depending upon the disease.

Common Pests That Attack Landscape Shrubs

Landscape shrubs are typically low-maintenance but are prone to insect problems. Many common pests that attack them are also problematic in hardwood trees.

One of the best ways to minimize insect damage is to regularly check your shrubs for infestations and then treat them quickly once found.

Aphids

These tiny, pear-shaped insects suck sap from leaves, causing distorted foliage and leaves to drop. As they feed, they secrete a sugary substance known as honeydew, increasing the chance of sooty mold growth.

Bagworms

Once in evergreen shrubs, bagworms are very hard to spot. They produce spindle-shaped cocoons that are hard to distinguish from the foliage. The dense cocoons incorporate leaves and twigs from the shrub, protecting the bagworms from pesticides.

Japanese Beetles

Japanese beetles do not harm your shrubs directly, but their feeding causes severe damage to their appearance. These beetles have a metallic green head and thorax, accented with copper-colored wing covers. They feed on the leaf tissues between the veins to skeletonize leaves.

Lace Bugs

Lace bugs get their name because their thorax and forewings have semitransparent cells that give their bodies a lace-like appearance. Adults and nymphs feed on the bottoms of leaves, sucking fluid that causes leaf stippling and bleaching.

Leafminers

Adult leafminers lay their eggs within the leaf tissues. Once the eggs hatch, the larvae feed between the lower and outer leaf surfaces, creating tunnels that puff up to look like blisters. If the population is high, they can defoliate an entire shrub and may kill the shrub if it’s smaller or weak.

Mealybugs

Mealybugs typically form colonies on the bottom of leaves or in the crook of branches, feeding on the sap in the foliage. Your shrub may appear stunted, and leaves may look deformed. These pink, soft-bodied insects are typically covered with a white, almost cottony-like material that protects them from the heat.

Scale Insects

Scale comes in two types — soft and armored — with both looking like little brown bumps on the leaves and branches. These tiny insects are typically between one-eighth and one-half inch in size and cause the leaves to wilt and prematurely drop off the shrub. If untreated, they can cause branch or stem dieback.

Spider Mites

Spider mites are another sap-sucking pest typically found on the bottom of the leaves. They are challenging, though, because they may create a heavy infestation before you notice them. A shrub with spider mites may have stippled, discolored leaves, an overall yellowing of foliage, or spider-like webbing between the branches or foliage.

Whiteflies

Whiteflies are usually pale in color and often mistaken for small white moths. They are sap-suckers and cause stunted growth, yellow leaves, and leaf drop. Compared to some pests, they can be hard to treat because they take flight when you disturb the host plant.

Wood Borers

Wood borers are different types of beetles that usually spend their life burrowing through stressed or dying shrubs, feeding on the wood in the branches and stems. Some borers will attack healthy trees too. The holes they create can weaken the limb, leaving your shrub prone to wind damage during storms.

How to Treat Pests in Your Landscape Shrubs

The first thing is to try to remove pests by hand. This is helpful with larger bugs like bagworms or Japanese beetles but might be inefficient for smaller insects.
Once you’ve removed what you can, spray your shrubs with a stream of water to knock as many off as possible.

Then apply insecticidal soap or neem oil, covering the leaves’ tops and undersides.

If these treatments are ineffective, spray your shrubs with a chemical pesticide and follow label directions.

Why Are Parts of My Shrub Dying?

It is disappointing to see parts of your shrub turning brown and dying, especially if you are unsure of the culprit. The first thing to check is for nutrient deficiency or toxicity and then look for pest or disease problems. If that isn’t the problem and you’re struggling to figure out what’s going on, here are some of the most common reasons your shrub could be dying.

Getting Too Much or Not Enough Water

Watering your shrub correctly can be a struggle, especially when the weather is hot. Too little or too much water can cause stress in your shrub, which may result in leaves turning brown and dying.

Not Suitable for the Area

When buying shrubs for your landscape, you have to ensure they are suitable for your local climate and your yard. If they aren’t hardy enough to handle the winters or not robust enough to take the heat of your summers, the extreme weather will turn leaves dry and dull, and it may cause the branches to die.

Also, is it planted in the right location regarding sun exposure? If it’s getting too much sun or too little, you will see signs your shrub is struggling.

Unusual or Drastic Weather Changes

A common problem seen in shrubs occurs when a streak of warm weather comes in late winter. Warmer temps prompt the shrub to start growing, but when the temps drop again, that growth stops and may be damaged by the cold. Also, if the ground is frozen, the roots can’t take in water to keep the growth green, and it dies.

Lack of Sunlight in the Center of the Shrub

If your shrub is too thick through the middle, sunlight won’t make its way to the leaves. This lack of light causes the leaves in the shrub’s center to drop, leaving interior branches looking dead and sparse.

Ineffective Root Growth

Shrubs need healthy, robust root systems to absorb water and soil nutrients. When the roots fail to develop or grow out into the surrounding soil, root growth may shrink or die, which will trigger death in the parts of the shrub above ground too.

Poor root growth may be due to overly sandy or clay-like soils, a compacted root ball that wasn’t trimmed or loosened at planting, or compacted soils around the roots.

Rabbit or Deer Damage

Another reason you may see branches die is because of rabbits and deer in your yard. They come in, looking for food, and strip patches of bark off the branches they can reach, especially in the winter when food is scarce. Once they strip the bark, these branches are susceptible to dying.

Other Common Pests Affecting Succulents and How to Treat Them

Thrips

Thrips are more attracted to a dry environment and dislike moisture, meaning they’re a natural predator for cacti and other succulents. The most difficult thing about thrips is knowing that you have them. These insects are very tiny, and it’s easy to miss them if you’re not paying close attention. It is more likely that succulent owners will notice the damage they leave behind. Thrips cause discoloration on the leaves or stem of affected plants. The damage could be brown, black, or even silver, and looks like streaks or trails where the insect has moved around. You may also see tiny black specks of waste that thrips leave behind. On top of that, your succulent may look generally stressed and unwell if the damage is extensive.

Spider Mites

Like thrips, spider mites are attracted to dry conditions and tend to avoid moist and humid environments, meaning they are often attracted to succulents. Spider mites can be identified by the webbing that they build on plants, usually between the joints and on the underside of leaves. You may also see small brown dots on the leaves, especially tender new leaves. This indicates the damage where the mites have been feeding on the juices. Spider mites can be a variety of colors including red, brown, yellow, or green. While they are difficult to spot, adult spider mites can be seen moving around on their webs.

Treating Succulents Affected by Thrips or Spider Mites

Thrips and spider mites can easily move from one plant to another, so the first thing to do if you’ve spotted these pests on your succulent is to isolate it from the rest of your collection to try to prevent them from spreading to other plants.

In the case of a severe infestation, you may need to prune off the affected areas and throw them away, or even throw out the whole plant. Sometimes it isn’t worth saving a plant that has a lot of insects on it. Otherwise, thrips and spider mites can be treated by spraying the plant with a strong stream of water to knock off the insects. This will need to be repeated periodically to be sure that all of them are removed.

It is also a good idea to treat the plant with a mild insecticidal soap or neem oil. Be sure to check that the treatment method is suitable for the type of succulent you have, and follow instructions carefully to avoid damaging or stressing the plant further. Vegetable oil or rosemary oil is also effective against these pests, as is a diluted rubbing alcohol mixture.

The most important factor in getting rid of insects and keeping them away is to be diligent and monitor your succulent collection closely. It generally takes multiple treatments to completely eradicate pests, but it isn’t difficult or expensive to treat them.

TIP: Prevent pests from attacking your succulents.

While it may not be possible to avoid all pests, you can do several things to limit the chances of bringing spider mites, mealybugs, and other insects into your home. Before buying a new plant, inspect it carefully for signs of insects and don’t buy any infested plants. Quarantine new plants away from the rest of your collection for a couple of weeks.

Neem oil can be used periodically to prevent and treat a variety of problems, including pests. It can be sprayed on a plant or used as a systemic insecticide via a soil drench.

Common Pests Affecting Succulents and How to Treat Them

Anyone who keeps succulents or other indoor plants will eventually have to deal with pests — it’s an unfortunate fact of plant ownership. Although succulents are not the most vulnerable to insect damage, they can be preyed upon by insects that suck on their juices, leaving the leaves damaged and the plant weakened.

Certain types of succulents (including many Echeverias, Crassulas, and Kalanchoe species) have a waxy coating on their leaves called farina or epicuticular wax that can help keep insects at bay. This substance looks like a very fine white powder on the leaves, so if your succulent has this, don’t wipe it off! It’s beneficial for the plant.

Mealybugs and Scale

These two common houseplant pests are closely related (mealybugs are actually a type of soft scale), with similar behaviors and treatment options.

Mealybugs may not look like insects at first glance, but once you know what they look like, they are unmistakable. These small pests can be up to ⅓ inches long, and they are white and fuzzy-looking. You will usually find mealybugs clustered together on the underside of leaves or near any joints in the plant.

Scale insects are often overlooked because there are many different shapes, sizes, and colors. The most common type of scale is a brown, dome-shaped insect. Once they are mature and have attached themselves to the plant, they don’t move. Their color and shape allow them to blend in with the natural bumps on many plants. When there are a lot of scale insects on a plant, they become more noticeable. They usually cluster around leaf joints or veins.

Treating Succulents with Mealybugs or Scale

These types of insects can be treated by using a cotton swab dipped in alcohol to kill visible insects by dissolving their protective coating. This method is safe for plants and works well, but requires diligence to make sure that all insects are removed. This method is best if there are just a few scale insects or mealybugs present. A strong spray of water can remove mealybugs but is usually not effective against scale insects since they attach themselves to the plant firmly.

For more serious infestations, a diluted alcohol spray (one part alcohol to three parts water) or insecticidal soap spray covers more of the plant’s surface in a short time, but may cause damage to succulents and cacti. Be sure to test it on a small area before spraying the whole plant. Also know that scale insects can live in soil, so you may want to repot your succulent if you have recurring infestations. Be sure to sterilize your pot before using it again.

Troubleshooting Leaf Loss

When a succulent starts dropping leaves, it can be really alarming. And there are lots of reasons that succulents lose leaves, so figuring out what’s wrong isn’t always straightforward. This section will list the most common reasons for leaf loss, and how to narrow down what’s happening with your particular plant.

Overwatering

Too much water is a common culprit for all sorts of problems with succulents, including leaf loss. If you’ve overwatered, the leaves (especially toward the bottom of the plant) will feel soft and mushy, and they may turn yellow or transparent.

Underwatering

Although it’s much less likely that you’ll underwater your succulent than overwater it, a neglected succulent will lose leaves. The leaves will be wrinkled and dry-looking, and some leaves may turn brown before they drop off the plant.

Lack of Sunlight

Succulents need plenty of sun — a minimum of six hours of bright, indirect light is a good guideline for most succulent species. When a succulent is kept in a spot that doesn’t get enough light, it will start to get a stretched appearance. That means that the plant will get taller (as it reaches toward the light source) but have a lot of space between the leaves. Leaves can fall off, and new leaves will be smaller than established ones.

Extreme Temperatures

Succulents naturally come from dry, warm climates, and they do well in most homes where temperatures are kept relatively constant year-round. But if your succulent gets exposed to very hot or very cold temperatures, that can cause leaves to get damaged and fall off. If the succulent is exposed to too much heat, its leaves may turn red or orange, or look dry and wrinkled before they fall off. If it gets cold and frost-damaged, the tips of its leaves are likely to turn soft and brown or black.

Overfertilization

Succulents don’t need much (if any) fertilizer, so it can be easy to overdo it if you are fertilizing your succulent houseplants. Leaves will drop off suddenly, and the plant may look weak overall. If you’re going to fertilize your succulents, restrict it to the summer growing season only, and dilute the fertilizer to half the strength recommended on the instructions.

Natural Leaf Drop

This one is good news: As succulents grow, they naturally lose some leaves toward the base of the plant. In this case, the leaves that drop off may turn brown and dry up before dropping off, or they might look perfectly normal before they fall. If your plant is losing lower leaves occasionally, and is otherwise healthy, there is no need to worry.

Root Rot in Succulents

Succulents and cacti are prone to getting overwatered and developing root rot, even more than other popular houseplants. If you follow proper watering practices and keep your succulent in well-draining soil in a container with drainage holes, it should be possible to avoid root rot. But sometimes well-intentioned plant owners love their succulents a little too much and end up killing them.

Root rot occurs when waterlogged soil prevents roots from taking in oxygen, or when any of several varieties of fungus grow in the overly wet environment.

Identifying Root Rot

The first signs of overwatering are yellow, mushy leaves that drop off the plant easily. If the problem is not resolved at this point, the leaves and/or stem of the succulent will turn brown or black. It will be difficult to save a succulent at this point, but it may still be possible. The section below will detail how to prevent and cure root rot.

Preventing Root Rot

It’s much better to avoid root rot in the first place than to try to cure it. Succulents store a lot of moisture in their stems and leaves, which allows them to live through periods of drought. But that also means that people tend to give them more water than they need, because their soil seems dry.

Proper watering practices are key to preventing root rot. Only plant succulents in containers with drainage holes, and use a chunky, free-draining soil to keep the roots from staying too moist. Only water when the soil is completely dry. If there’s any doubt, wait a few more days. Remember, succulents are made for dry conditions, and they are very resilient.

Curing Root Rot

If your succulents have already developed root rot, it may still be possible to save them, depending on how much damage has been done. The first step is to carefully remove the plant from its pot to see what the roots look like. Remove as much soil as you can, and trim off any roots that are black or dark brown or that feel mushy or slimy.

Let the plant air dry for a day or two, leaving the roots exposed. Once the roots feel dry to the touch, you can replant it in fresh potting mix. Be careful not to subject your succulent to any unnecessary stress (direct sun, temperature extremes, etc.) while it recovers. In most cases, as long as there are healthy roots left, your succulent will bounce back in a few weeks. If the roots are totally rotted and unhealthy, you might be able to save some healthy stems or leaves and propagate a new plant from those instead.