Demystifying Dark Spots on Poinsettia Leaves

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I’ve seen a lot of poinsettia leaf problems over the years, both in stores and from readers. Here are some of the common questions I’ve been asked over the years. I hope you find your answer here.

Poinsettias are synonymous with the holidays their brilliant red and green bracts bringing festive cheer. But those vibrant leaves can sometimes take an unfortunate turn, developing unsightly dark spots. If your poinsettia’s pristine presentation has been tainted by these blemishes, read on to understand the common causes and best remedies.

What Causes Dark Spots on Poinsettia Leaves?

Poinsettias are susceptible to several pathogens and environmental stressors that manifest as dark lesions on leaves Common culprits behind the spots include

  • Fungal diseases – Botrytis leaf spot, and powdery mildew fungi leave round black or brown spots. High humidity encourages these pathogens.

  • Bacterial diseases – Bacterial leaf spot manifests as small dark lesions, often surrounded by yellow halos.

  • Cold damage – Chilling injury causes black, collapsed areas on leaves. Dark scorched spots can also develop from heat stress.

  • Nutrient deficiencies – Lack of nutrients like nitrogen, calcium, and magnesium leads to necrotic dead zones.

  • Overwatering – Excess moisture damages roots, resulting in leaf spots.

  • Chemical phytotoxicity – Overuse of fertilizers or pesticides can burn leaf tissue.

In most cases, the dark blemishes result from improper cultural practices that allow pathogens to attack or create physiological stress.

Effective Treatments for Dark Leaf Spots

If those unsightly spots appear, taking prompt action provides the best chance of recovery:

  • Prune affected leaves – Remove all leaves showing symptoms to limit disease spread. Sterilize pruning shears between cuts.

  • Improve air circulation – Good airflow reduces humidity levels that contribute to fungal and bacterial diseases.

  • Apply fungicidal sprays – Commercial fungicides containing chlorothalonil or propiconazole can treat active infections.

  • Treat with copper compounds – Copper fungicides help suppress bacterial leaf spot. Always follow label directions.

  • Leach excess fertilizer – Heavily flush soil if chemical burn is causing the spots.

  • Alter watering habits – Allow soil to dry out between waterings to prevent oversaturation.

  • Move plant – Relocate poinsettia away from drafty areas or heat vents causing temperature stress.

  • Add grow lights – Supplement natural light if low levels are suspected, especially in winter.

Rapidly implementing corrective care is critical to halt the spread of damaging spots.

How to Prevent Dark Spots on Poinsettia Leaves

While treating active infections is important, prevention is the best policy when it comes to poinsettia leaf spots:

  • Choose disease-resistant varieties – Look for cultivars bred to deter common pathogens.

  • Inspect plants before purchase – Avoid pre-infected plants by examining for spots at the nursery.

  • Provide proper light – Place poinsettia in bright indirect sunlight to avoid stresses from too much or too little light.

  • Monitor humidity – Use a humidifier or pebble tray to keep humidity between 40-60%.

  • Promote air circulation – Grow poinsettia in areas with continuous gentle airflow.

  • Avoid excess fertilization – Overfeeding increases susceptibility to some pathogens.

  • Use sterilized pruning tools – Disinfect shears after use on diseased plants to avoid spreading infection.

  • Allow soil to dry out between waterings – Check with a finger to gauge moisture levels and prevent oversaturation.

  • Water early in the day – So foliage dries fully before nighttime when humidity is higher.

  • Remove spent flowers – Prune off old flowering bracts which can harbor pests and diseases.

With attentive, preventive care, poinsettias can stay vibrant and spot-free from purchase through the holiday season.

Common Poinsettia Leaf Spot Diseases

While general environmental stress can cause leaf spots, specific fungal or bacterial diseases are often the culprits. Learn to identify these common poinsettia pathogens:

Botrytis Blight

  • Caused by the fungus Botrytis cinerea
  • Produces water-soaked gray lesions that expand rapidly
  • Thrives in cool, humid conditions with poor air circulation
  • Can spread quickly and destroy entire plants

Powdery Mildew

  • Identified by white powdery coating on leaf surfaces
  • Caused by several related Erysiphe species fungi
  • Favored by crowded conditions and dry air
  • Stunts growth and distorts young leaves and bracts

Leaf Spots

  • Circular to irregular brown or black spots with yellow halos
  • Diverse fungi like Alternaria, Cercospora, and Colletotrichum
  • Associated with wet foliage and high humidity
  • Can lead to defoliation with repeated infection

Bacterial Leaf Spot

  • Small dark water-soaked spots, often surrounded by yellowing
  • Caused by the bacterium Xanthomonas axonopodis
  • Spreads rapidly by splashing water
  • Leaves become curled and twisted in advanced stages

Familiarize yourself with the appearance and conditions favoring these common diseases. This allows swift treatment at first signs of infection.

Providing Optimal Care Conditions

The best offense is a good defense when it comes to preventing poinsettia problems. Grow robust, resilient plants by providing proper care:

  • Light – Place in bright filtered light. Supplement with grow lights if natural light is insufficient.

  • Temperature – Maintain between 60-70°F. Avoid cold drafts and excessive heat.

  • Water – Check soil moisture regularly. Water thoroughly only when the top inch becomes dry.

  • Humidity – Ideal levels are 40-60%. Use a humidifier or pebble trays to elevate humidity.

  • Soil – Use a well-draining potting mix. Amend denser soils with perlite or vermiculite.

  • Fertilizer – Apply diluted balanced fertilizer every 2-3 weeks during active growth periods.

  • Pruning – Remove spent flowers/leaves and shape plants by cutting back leggy stems.

Monitoring conditions and responding promptly to any changes minimizes environmental stresses. This keeps poinsettias growing vigorously and better withstands threats from disease.

Enjoying Poinsettias Year After Year

While prized as decorations, poinsettias don’t need to be tossed after the holiday season ends. With proper care, they can be kept as attractive houseplants all year long:

  • Cut back on water and fertilizer during winter rest periods after bracts drop.

  • Prune back hard in spring to encourage fresh growth. Repot at this time if rootbound.

  • Move outdoors to a shaded spot during summer. Fertilize monthly.

  • Bring back indoors in early fall. Place in complete darkness from 5pm to 8am daily to initiate reblooming.

  • Discard plants if they fail to rebloom after a second cycle or become overgrown and leggy.

Don’t resign your poinsettias to the compost pile come December 26th! With attentive care and favorable conditions, you can enjoy months of additional beauty from these holiday superstars.

So don’t dismay if your poinsettia develops some of those undesirable dark spots. Follow the remedies outlined here to get your plant back to its former vibrant self. And focus on prevention by providing the light, moisture, and humidity poinsettias crave. Do your part to keep the holidays bright, and your poinsettias will thank you with an extended colorful display.

What has caused the black edges on my bracts, will it spread on this plant or onto others? What can I do for it?

Doug says the black or brown, crispy edges on the leaves are because of the change in humidity and watering from the greenhouse to the house. Your house is much drier than the greenhouse and this is what has happened. Nothing you can do to reverse this process on existing leaves.

Do not overwater the plant – this is another partial cause of tip and leaf browning.

We purchased a poinsettia two days ago and the ends of the red blooming leaves are drying up and turning black.

We did not expose the plant to cold weather. And we have carefully managed the watering to not over-water or not enough watering (ie. We used the finger wetness test daily). Also, we have the plant located in a bright location. What do you think might be the problem?.

Doug says that when plants move from a place with a lot of humidity, like a greenhouse, to a place with very little humidity, like a house in the middle of winter, the leaf tips and bracts usually turn black. There are other causes but that’s the biggie.

The Secret to Keeping Your Poinsettia Alive ALL YEAR

What causes dark spots on poinsettia leaves?

Leaf spot is another common disease that affects poinsettias. It is caused by various fungal pathogens and appears as dark spots or lesions on the leaves. These spots may vary in color from brown to black and can lead to leaf drop if left untreated. To treat leaf spot, remove any infected leaves from the plant and dispose of them in a sealed bag.

How do you know if a poinsettia has leaf spot disease?

The most common signs of alternatia leaf spot disease are brown or blackish spots on the leaves. These spots can start off small, but if left untreated, can grow to the size of the entire leaf. In its advanced stages, this disease can cause the leaves of your poinsettia plant to fall off.

Do poinsettia leaves turn black?

The black leaf spots and sunburned leaves will likely not recover, so trim them. However, mildly sunburned foliage should remain, especially if the damage to the rest of the leaves is extensive. Your poinsettia leaves can turn black because of stem rot and root rot.

How do I know if my poinsettias need care?

When caring for your poinsettias, it’s important to keep an eye out for signs of distress in the leaves, which can indicate overall plant health. Watch your plant’s leaves for these signs: Yellow leaves on your poinsettia may be a sign of overwatering or poor drainage.

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