Damping-Off

Pythium, Rhizoctonia, and Fusarium species

Fungalalso: Seedling blight

The bane of seed starting, damping-off is the sudden collapse and death of seedlings at or just below the soil line. Seeds may rot before they sprout, or healthy-looking seedlings can topple over within a day. It is caused by several soil-dwelling molds and fungi and is driven by cold, wet, overcrowded growing conditions.

🔎 How to spot it

Look for seeds that fail to come up, or seedlings that develop a thin, water-soaked, pinched, brown or black spot at the stem base and then flop over and die. The stem looks like wire or thread where it has collapsed. It often shows up in patches that spread outward across a tray, sometimes with a fine white mold on the soil surface or on fallen seedlings.

🥀 Damage it causes

Damping-off kills seeds and young seedlings outright, often wiping out patches or whole trays in a day or two before plants ever reach the garden. Seedlings that survive a mild brush with it can be stunted, with weakened roots that never fully recover.

🔬 What causes it

Damping-off is caused by soil molds and fungi, most often the water mold Pythium along with Rhizoctonia and Fusarium, that survive in old soil, dirty pots, and debris and spread through wet media and shared water. They strike hardest when seeds sit in cold, soggy, poorly drained mix that slows germination, and they ride in on reused tools, unwashed containers, and hose ends dragged through dirt.

🛡️ Prevent it

Start seeds in clean containers and fresh, sterile seed-starting mix, never garden soil, and wash and sanitize reused pots and tools. Sow at the right depth and wait for warm media, about 65 to 70 F, often with a heat mat, so seeds sprout fast. Avoid overwatering, let the surface dry slightly between waterings, give good light and airflow, and do not crowd seedlings.

🧯 If it is already here

There is no cure once a seedling collapses, so remove affected seedlings and the soil around them immediately. Improve the conditions for the rest: more warmth, more air movement, brighter light, and less water. Letting the surface dry and running a small fan over the tray often halts the spread. Badly affected trays are best discarded and restarted with fresh, clean mix.

💡 Good to know

Prevention is everything with damping-off, because it moves too fast to treat. Bottom watering, a fan for air movement, and a thin layer of dry vermiculite on the surface all help keep the crucial stem zone from staying wet. Warm, fast germination is the best protection, since the pathogens hit slow, struggling seedlings hardest.

🌱 Plants it affects

714 plants in the library can be affected by this problem

Acorn Squash

Adirondack Blue Potato

Aji Amarillo Pepper 🍓Albion Strawberry

Alice du Pont Mandevilla 🥔All Blue Potato

American Beauty Dragon Fruit

American Beech

American Persimmon

Amethyst Falls Wisteria

Annabelle Smooth Hydrangea

Arizona Sun Blanket Flower

Atlantic Giant Pumpkin 🥕Atomic Red Carrot

Aucuba

August Beauty Gardenia

Aunt Molly's Ground Cherry

Barbara Karst Bougainvillea

Beauregard Sweet Potato

Becky Shasta Daisy

Bee Balm 🍅Beefmaster Tomato

Benarys Giant Zinnia

Bengal Tiger Canna

Better Boy Tomato 🥬Bibb Lettuce 🍅Big Beef Tomato

Black Beauty Eggplant

Black Beauty Zucchini

Black Beluga Lentil

Black Cherry Tomato

Black Crowberry

Black Currant 🍉Black Diamond Watermelon

Black Kabouli Chickpea

Black Krim Tomato

Black Raspberry

Black Sapote 🥬Black Seeded Simpson Lettuce 🥕Black Spanish Radish

Black Tartarian Cherry

Black Walnut

Black-Eyed Pea

Black-eyed Susan Vine

Blood Orange

Bloomsdale Spinach

Blue Bird Delphinium

Blue Bird Rose of Sharon

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.