9 Poinsettia Diseases to Watch for This Season

This canker comes from infections by the Curtobacterium flaccumfaciens pv. poinsettiae bacterium. It’s common in cultivation, where many poinsettia plants grow together in a small space. Your plant may pick it up from the store you bought it from. Look for water-soaked lesions on leaves and stems. They’ll start yellow and brown, then grow black and fuzzy as the plant slowly succumbs to the disease.

Prevent bacterial canker by avoiding overhead irrigation. Water plants at the base of their pots instead, and be sure to space them properly. Grant two to three feet of distance between two poinsettias, allowing air to pass through them. Inspect recently purchased plants closely to ensure they don’t have lesions, dying stems, or amber-colored liquid seeping from their wounds.

Bacterial canker is incredibly difficult to treat once it infects your poinsettia. It may be best to discard the plant and try again. This is especially true if you have more than one poinsettia, as you’ll want to avoid spreading the bacteria to healthy specimens. Organic copper fungicides prevent infections from spreading—apply them at the proper dosage according to their instructions.

Look for soft, mushy stems on young cuttings. The mushiness spreads upward, killing infected plants. Older specimens may lodge—this is a process where the stems fall over after they grow mushy and weak at the base. These old plants may seal off the wound and heal, while cuttings and seedlings most likely die before they get better.

Always practice clean propagating when handling your plants. Sterilize pruners, knives, and containers before you use them. Find sterile growing media to start cuttings, and keep them under bright lights while they sprout roots. Avoid flooding plants with excess water; you want to keep their soil moist, not soggy.

Like bacterial canker, stem rot is difficult to eradicate once it spreads into a plant. Get rid of cuttings or old plants with the disease away from the growing site to avoid more infections. Apply an organic bactericide to mature plants while you take cuttings from them. It’ll prevent infections on both the cutting materials and your host plant.

Look for knobby, woody growths that look like tumors on your poinsettia. They’re reproductive sites for the bacterium Agrobacterium tumefaciens. Galls form at the base of the trunk, where the plant meets the soil. They also sprout on roots, or higher above the plant in rare occasions. Young galls have spongey tissue that compresses when you poke them.

You can avoid bringing crown gall bacteria into your home by inspecting new poinsettias carefully. Look for knobby growths on the stems and surface roots. Protect new transplants from infections by treating their roots with an antibiotic like Galltrol if you can find a store that sells it in your state. Otherwise, remove the plants and dispose of them.

Galls may disappear as established outdoor poinsettias age, becoming less of an issue for the plants. The bacteria stay in the soil where they can infect new susceptible plants. If your houseplant has a gall, it’s best to dispose of it and find a new one. Avoid using the container the poinsettia came in and burn or trash the infected plant.

Gray mold manifests as sunken lesions on mature stems. You’ll see brown spots on flowers, branches, and leaves on the upper stems. The lesions and cankers develop into fuzzy debris that spreads spores to new susceptible poinsettias.

This fungus is easily preventable and manageable. Practice hygienic cultivation techniques by carefully pruning stems to prevent wounds. Place poinsettias in bright indirect sunlight indoors and water them once the soil surface dries. Remove any infected parts as you see them to prevent spores from wafting in the air.

Gray mold commonly infects over 200 different plants! There are ample treatment options to minimize its spread. Organic copper or sulfur fungicides work w to reduce existing lesions and spores, but the disease can develop resistance to certain fungicides over time. Use these only as a last resort. Ensure each poinsettia has regular airflow, low humidity, and cool temperatures to prevent gray mold spores from spreading.

Watch for yellow spots on the tops and undersides of the leaves. They’ll develop fuzzy mildew growth that spreads spores to other plants when water splashes on them. The patchy fuzz sticks to the leaves, creating unsightly spots on your poinsettia.

Prevent powdery mildew by bringing disease-free poinsettias indoors. If your plant was outdoors during the summer, inspect it carefully before you bring it inside. Powdery mildew likes humid, dark conditions that are common in the shade of late summer. Give plants ample space during the growing season, avoid crowding, and remove any mildew growth as it pops up.

Start by pruning the damaged leaves away and then treat powdery mildew with an organic fungicide or a similar spray. Alternative options include potassium bicarbonate, the bacterium Bacillus subtilis, or even milk spray! Potassium bicarbonate works like a charm and is easily mixable. Use whichever option is easiest for you, and apply the sprays outdoors so you don’t inhale the fumes.

Root rot is hard to identify early on because it primarily spreads underground. Fungi, parasites, and other organisms can cause it. Watch for stunted growth, weak stems, and mushy roots. Mature plants with root rot will lose their leaves and flower prematurely before dying completely.

Prevent root rot by watering after the soil surface dries. Poinsettias appreciate consistent moisture but they don’t like soggy conditions. Letting the soil dry before you water helps their roots breathe, making them more resistant to pesky pathogens. Use fresh potting soil, clean containers, and sterile tools when handling your poinsettias for safe cultivation.

Protect your poinsettias from root rot by applying an organic fungicide to new potted plants or cuttings. If symptoms appear, isolate the infected plant from other poinsettias. Dispose of the dead or dying plants, and correct watering frequencies on your other houseplants to avoid soggy soil.

Look for brown circular marks on the leaves with yellow margins. The dots spread rapidly until the entire leaf turns yellow or brown and falls off. Severe infections may manifest in sunken, brown stem lesions that spread scabs with fuzzy spores. Stem lesions can lead to girdling, where the entire stem browns and falls off.

Scab spreads rapidly with high humidity and overhead irrigation. Water your plants at their base to avoid excessive splashing. Spray an organic fungicide on new poinsettias from the store to give them an immunity boost before you bring them indoors.

Once the scab spreads throughout your houseplant it is impossible to remove. It’s best to discard it and sanitize the area before trying again. Practice proper cultural conditions like low humidity and soil watering to prevent scab infections in the future. Inspect poinsettias at the store before buying them to ensure they’re scab-free.

Bacterial leaf spots start as small yellow or tan circles that mature into large, brown, and irregular marks on the leaves. The foliage crinkles and shrivels as the bacterial growth spreads further. Watch for markings on the top of the leaves where water may splash from overhead irrigation.

Prevent leaf spots from spreading by removing infected debris from the site. The bacterium prefers wet, humid conditions, so practice soil surface watering instead of overhead irrigation. If your house is humid, add a fan nearby or open a window for a few minutes to encourage air circulation.

Unfortunately, once bacterial leaf spot grows throughout your poinsettia there is little that can save it! You’ll have to get rid of your current plant and find a new one that’s pathogen-free. If you’d like to see if you can nurse it back, try removing any leaves with spots on them, and correct the cultural conditions to discourage the pathogen.

Inspect your poinsettia leaves’ undersides and tops to find orange or brown rusty growth. You’ll notice groups of circular rust spots that converge into larger patches. The mature rust patches form spores that float away when air or water disrupts the leaves.

Keep rust at bay by irrigating your houseplants on the soil surface instead of overhead. When watering, add enough moisture to make the dirt moist but not soggy. Ensure the leaves stay as dry as possible by not misting or humidifying the room. Space your plants wide enough apart to prevent potential spread of the fungus.

Help your infected houseplants by removing any rusty leaves or stems. Continue practicing prevention methods from above, and quarantine the plant from your other poinsettias while it heals. If rust persists, try a copper or sulfur organic fungicide spray to control the pathogen.