Why Are My Plant Stems Turning Black?

The stems of your plant start to darken is not something you’d like to see. Are you able to tell the plant’s on the verge of to end its life?

Blight, stem rot, the stem, and bacterial canker and other stem diseases are the most common causes of stems that are blackened. Other causes could be insect infestations, leaf and stem spots. These are typically the result of poor practices in the cultivation like overwatering, absence of sunlight, and temperatures stress.

Be calm and composed for the time since when the root problem is identified most issues can be resolved easily.

What Causes Plant Stem Turning Black?

[1] Early Blight

“Blight” is a term used to describe blight “blight” refers to a group of fungal diseases which cause the plant’s stems to become black. The term “blight” is derived from the nature of blight that is seen at the beginning of the season of growth. It usually occurs in springtime, from early to mid-spring.

This fungus Alternaria solani is the most frequent reason for early-onset blight. The fungus usually grows in soil, however it may also be found within dead plant material. In moist conditions of the early spring, spores can sprout.

The infection starts as small brown spots that are irregularly shaped or cuts on areas of the body that are near to the soil or ground.

The irregular spots will grow to form circles around the dead bull’s-eye. They appear on lower leaves, stems, and on the fruits on the plants.

The wounds will enlarge to become black and eventually, the stems will be covered. The affected leaves begin to become yellow, and then turn brown and then fall off. Fruits can also suffer the same fate, forming black cracks and falling.

Plants who are weak, stressed or malnourished are often affected. Warmer temperatures and damp conditions of between 80 and 85 degrees Fahrenheit (27-29 degC) can accelerate the process of stem blackening.

Black fireplace with house plants in front

Control and Management

  • Get rid of all plant debris to stop spreading the fungus.
  • Pruning or staking your plants frequently to increase the aeration of your plant and prevent fungal infections. It is essential to clean your cutting tools or shears following every trim.
  • Do not wet the leaves on your plants. The early morning irrigation of your plant in the morning can aid in drying the leaves enough.
  • Apply an fungicide based on copper (Check the most current cost at Amazon right here). Repeat the application each seven to 10 daysor for as long as is necessary

[2] Stem Rot

The fungus is often connected with root rot. Both are caused by fungi which affect the roots and stems when the soil is too moist. It can be the result of soil that is soggy or waterlogged due to overwatering or poor drainage or excessive humidity.

The leaves and stems are soaked while you water your plants is another cause. This is especially true when you are using overhead irrigation. Fusarium from those of the Phytophthora as well as the Fusarium families are among the top prevalent causes of stem rot.

Common symptoms are swelling of the stem as it softens, then turning into black, and then brown. The roots can also sink in the water, then die, and then begin to decay. They’ll be black or brown in color, and will feel soft between your fingers.

The affected stems usually will collapse and wilt and die, causing the plant to die. The leaves usually change color, and get brown spots, then wilt and fall.

Control and Management

  • The onset of rot on the stem is typically an indicator of a later-stage fungal rot illness. The chances of getting your plant back are zero.
  • The best option is to cleanse your plant of any infected areas. Cut off any diseased root leaves, stems, and even flowers (if they are affected).
  • Apply fungicide and plant your houseplant in a new pot.

[3] Late Blight

The late blight, as its name suggests is a fungal disease that is more prevalent during the growing season. In the majority in the United States, it appears in the months of September and October.

The late blight, similar to early blight, starts in the soil. Fruits, stems and leaves near the soil first begin to change color from black to dark brown. The first signs appear on the older leaves and branches that develop grayish-green, water-soaked lesions.

As the infection progresses the lesions begin to enlarge and then turn into black. A few white cottony growths could appear near lesions. Fruits that are infected could form black lesions too.

The affected foliage typically becomes yellow, and then it forms large black patches prior to disappearing from the tree. The affected leaves can appear to be bleached or scorched.

As the condition gets worse, your entire plant will become affected and will turn completely black. If you don’t treat it the plant will likely die within a couple of weeks.

The Phytophthora infestans fungus is responsible for late blight. It thrives in warm, moist conditions, with temperatures during the day between 70 and 80 degrees (21-27degC). It also likes cooler nights.

Control and Management

  • Make drastic steps to stop the spread of the blight. Eliminate and destroy all affected components. It is helpful to not reuse the cutting tool , without sterilizing it.
  • Do not reuse the medium you are growing.
  • Make sure to water your plant in the morning and try to avoid the overhead irrigation
  • Make sure to treat your plant with an fungicide based on copper or a broad-spectrum bio-fungicide (Check the most current prices at Amazon right here).

[4] Alternaria Stem Canker

Alternaria stem canker (also known as stem canker) is severe fungal infection that is caused by Alternaria fungus. The ugly, strangely-shaped cankers are usually found on the stems that are near to the soil. However, they can cause harm to leaves, fruits as well as flowers.

Alternaria stem canker symptoms are dark black or brown stem cankers. Circular encircles these irregular lesions. As they grow they may expand and darken.

There may be areas of brown or black within the veins of leaves. The fungus releases toxins that trigger these symptoms. The affected leaves usually wilt, becoming limp, and eventually disappear.

At temperatures of 77 degrees Fahrenheit (25degC) The infection rapidly spread.

Control and Management

  • The spread of stem canker is aided through overhead irrigation as well as high levels of humidity. It is recommended to increase ventilation in order to lower the humidity.
  • Remove and clean up all plant material
  • Make sure to treat your plants with any fungicide that is specifically designed for black fungus mold. I suggest a broad-spectrum product that contains fludioxonil and cyprodinil.
  • Avoid overhead watering as well as handling plants that are wet.

[5] Bacterial Canker

Bacterial canker is a cause of black sunken and sticky lesions on the stems of your plants. They usually appear in the spring season. The lesions usually release an unpleasant sap, which causes the area surrounding to get moist and change brown or black.

The leaves above those stems affected will exhibit signs of stress, too. Curling, yellowing and dead spots will be visible on leaves. If the infection is serious enough, the leaves will begin to fall off.

The growth rate often slows down, which results to stem dying. The plant is eventually going to die.

The pathogen that causes stem-canker infection is Pseudomonas Syringae. The opportunistic bacterium can be found in wounds that result from cuts, injuries, etc. Bacterial canker can be quite agresive in cool and wet conditions.

Control and Management

  • Get rid of dead, wilted or damaged leaves and stems.
  • It is a good idea to prune during the flowering season. Do not prune in the fall or spring.
  • Cuts to pruning should be treated immediately with the Grafting wax (Check the most current prices at Amazon right here).
  • Check soil pH. Make adjustments with lime if the soil is too acidic
  • Based on my experience, I’ve found copper sprays work against bacteria that cause cankers. If the spray contains the acid phosphorus, it’s you’re in better shape.

[6] Botrytis

Botrytis is a gray-colored mold that is visible on stems in large tan and grayish spots. Botrytis spores are dusty or fuzzy gray, and they grow on moist stems and foliage. They germinate and flourish in humid conditions that is cool and warm.

Spores get into the tissue through cracks in the leaves and stems. The patches of gray will eventually join and create black blotches on stems. The most common occurrence is on lower and older stems.

Botrytis also causes destruction on foliage and flowers. It can cause greyish mold to saturate the leaves, blocking photosynthesis.

It is rapidly spreading and causes the affected regions to shrink. The stems and leaves affected by the disease will curl or droop and then wither.

Control and Management

  • Eliminate infected plants from other plants immediately.
  • Cut off any moldy areas and dispose of them in a proper manner. Make sure to wash your hands, tools, and equipment to stop the spread of fungus spores.
  • Move the plant in a more aerated and warm location with less humidity
  • Dry your plant completely prior to applying an aeration spray
  • Be careful not to injure the plant (Source: Pennsylvania State University)

[7] Black Stem Rust

The rust on the back stem is among of the most frequent fungal diseases that can wilt the stems of plants. The most often exposed areas of stems. Rust is also visible on fruits, leaves and flowers.

Stem rust can cause spore pustules which are at first white, but later turn greenish-yellow. They eventually become dark brown or black, and then suffocate the entire stem. High humidity, warm temperatures and low light levels promote their growth.

Common symptoms are:

  • The black spores are visible on the stems and leaves in the fall and late summer
  • The cocky black blotches appear on the infected stems
  • The affected leaves turn yellow and fall off early
  • A prolonged infestation may cause the stunting of growth

Control and Management

  • A clean and healthy environment is essential to stop the spread of the spores
  • Remove and cleanly dispose of the plant debris that has fallen
  • Make sure you keep the overhead watering off and avoid soaking the foliage
  • Applying fungicides that have sulfur, pyrethrin or copper can help in reducing the rust on the stem.

[8] Spring Black Stem and Leaf Spot

Spring leaf spot and stem that is black is a fungal infection that thrives in damp spring weather. Fungal Phoma mediciaginis is the cause of spot disease.

The black spots are most often seen on the stems and leaves as signs. The lesions show up quickly on the stems, and then turn into black. The entire stem may turn black as they expand and become amorphous.

Lesions on leaves tend to be irregular in their shape and grow into massive streaks. The leaves that are affected by the disease wilt and drop off the plant, becoming yellow. If the black lesions on leaves and stems become too large, the plant will be affected by the disease.

Control and Management

  • Remove infected leaves and stems immediately if you notice the appearance of lesions or black marks.
  • I strongly suggest planting cultivars that are resistant to spring black stems as well as leaf spot.
  • There are a variety of fungicides available on the market that claim to reduce spring black stems as well as leaf spot. I would still recommend applying a systemic or broad-spectrum fungicide.

[9] Summer Black Stem and Leaf Spot

The leaves and stems are black. It’s a fungal illness that thrives in humid, warm conditions. It is due to the fungal fungus Cercospora mediciaginis. It can be found in the foliage and stems.

The symptoms include:

  • Brown spots with curly edges appear on leaves at first. They may turn grayish or silvery and then be cut by yellow
  • The stems are covered with brown lesions. They eventually turn black.
  • Lower leaves are lost

Control and Management

  • Temperatures that are too hot and high humidity can cause summer black stems as well as leaf spot. Therefore, it’s recommended to move the plant into a cool location that has less humidity.
  • Remove infected areas and dispose of them in a safe manner
  • The use of copper hydroxide fungicides may help in preventing the black stem of summer and the leaf spot disease.

[10] Insect Infestation on Stem

Certain pests that are common be found on the stems, and cause the stems to turn black. This is usually seen when the problem is caused by sap-sucking insects. This includes mealybugs, scales, aphids and whiteflies and real bugs.

The pests typically excrete an odourless, sugary substance. The honeydew is referred to as the honeydew. gooey substance is a popular source of food for mold growth. In the end, stems, leaves and even the flowers can be sticky and grow black, sooty mold.

Another sign that is commonplace can be the appearance insects. They also enjoy eating honeydew, and could even shield the pest responsible.

Control and Management

  • The measures to control the pest will be based on the kind of pest.
  • Remove and prune the plants that are infested.
  • It is possible to manually handpick or label bugs as mealybugs by using cotton swabs containing alcohol.
  • A powerful water jet can assist in removing bugs , including whiteflies, mealybugs, fungus gnats and Aphids.
  • To treat the problem, you can apply an insecticidal shampoo, oil of neem, or insecticides containing pyrethrin.
  • I also like using natural predators such as the parasitic wasps and lacewing larvae.

How to Prevent Plant Stems Turning Black

  • Make sure you have adequate ventilation Space your plants, trim them and stake them to increase the aeration
  • Use good hygiene – avoid working with plants that are wet and remove all the debris, and clean cutting tools after each use.
  • Proper watering practices – Beware of overhead watering, do not sprinkle water on foliage, and make sure to water it early in the early morning.
  • Do not reuse the growing mediums.
  • Maintain your plants’ health – Fertilize according to the needs and use an abundant potting mix, provide adequate light and stay clear of low light.
  • Remove infected or infested plants as soon as you notice signs of infection.


Went from a bad gardener to a half-decent one over 10+ years. Super happy to share my tips and tricks with you :)