Charcoal Rot

Macrophomina phaseolina

Fungalalso: Macrophomina, Macrophomina root rot, Charcoal stem rot, Ashy stem blight

A hot-weather, soilborne rot caused by a fungus with an enormous host range, named for the sooty, charcoal-like dusting of tiny black survival bodies it leaves in rotted tissue. It is a stress disease that strikes hardest when plants are hot and drought-stressed, causing sudden wilting and collapse.

🔎 How to spot it

Plants show water stress and then wilt and collapse, often suddenly in hot weather. Cutting into the crown, lower stem, or roots reveals reddish-brown to black necrotic tissue, and the rotted tissue and woody vascular ring are peppered with countless tiny black microsclerotia that look like ground charcoal or pepper. Shredded, gray-black lower stems are common in some crops.

🥀 Damage it causes

The rot kills crown and root tissue, so plants lose vigor, wilt, ripen or die prematurely, and yield poorly, and badly affected plants collapse outright. Losses are worst in hot, dry seasons and on light, sandy soils, and the disease can take down patches of a planting.

🔬 What causes it

The fungus Macrophomina phaseolina, which survives in soil and crop debris as long-lived microsclerotia for years and infects more than 500 plant species. It is a stress pathogen: disease explodes with high temperatures (around 86 F), drought and water stress, sandy soils, and heavy fruit load, and builds up when susceptible hosts are grown in the same ground repeatedly.

🛡️ Prevent it

Because it is a stress disease, the main defense is keeping plants from getting hot and dry: irrigate evenly to avoid drought stress, mulch to cool and conserve soil moisture, and avoid overcrowding and overloading plants. Rotate away from susceptible hosts to less-susceptible cereals or grasses, and remove and destroy infected debris.

🧯 If it is already here

There is no rescue treatment once plants collapse, so management is preventive. Pull and destroy affected plants, keep the rest well watered to ease stress, and plan rotation, resistant varieties, and good soil moisture for the next crop. In intensive plantings, pre-plant soil treatments such as solarization or fumigation are used to lower the soil inoculum.

💡 Good to know

The charcoal-dust look of the microsclerotia in split stems and roots is the diagnostic sign. Anything that reduces heat and drought stress, especially steady irrigation, does more than any spray to hold this disease down.

🌱 Plants it affects

213 plants in the library can be affected by this problem

Acorn Squash

Adirondack Blue Potato

Adzuki Bean

Agapanthus

Aji Amarillo Pepper 🍓Albion Strawberry 🥔All Blue Potato

Atlantic Giant Pumpkin

Banana Pepper

Beauregard Sweet Potato 🍅Beefmaster Tomato

Better Boy Tomato 🍅Big Beef Tomato

Big Boy Tomato

Bitter Melon

Black Bean

Black Beauty Eggplant

Black Beauty Zucchini

Black Cherry Tomato 🍉Black Diamond Watermelon

Black Kabouli Chickpea

Black Krim Tomato

Black-Eyed Pea

Blue Fescue

Blue Lake Green Bean 🥒Boston Pickling Cucumber 🍅Box Car Willie Tomato

Brandywine Tomato

Broad Windsor Fava Bean

Carolina Reaper Pepper

Charleston Gray Watermelon

Cherokee Purple Tomato

Cinderella Pumpkin

Costata Romanesco Zucchini

Cranberry Bean

Crenshaw Melon

Crimson Sweet Watermelon

Denim n Lace Russian Sage

Distylium 🥒Diva Cucumber

Dusty Miller

Early Girl Tomato

Edamame 🥒English Cucumber

Fordhook 242 Lima Bean

German Butterball Potato 🍅German Queen Tomato

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.