Root Rot

Plant disease

Description

Root rot is a general name for the decay of plant roots, not a single disease with one scientific name. It can result from prolonged waterlogging and lack of oxygen, or from pathogens such as Phytophthora, Pythium, Rhizoctonia, and Fusarium. Poor drainage often creates conditions in which roots weaken and pathogens spread. Damaged roots cannot take up enough water and nutrients, so the plant may wilt even while its soil is wet. Leaves can yellow or drop, growth may slow, and seedlings may collapse. In advanced cases, decay can extend into the stem base and kill the plant. Root rot affects vegetables, ornamentals, houseplants, shrubs, and trees, but the causes and severity vary. It may develop quickly in warm, saturated potting mix or progress over a longer period outdoors. Because aboveground symptoms resemble several other problems, examining the roots is important before choosing a treatment.

Symptoms

• Yellowing leaves
• Wilting
• Stunted growth
• Leaves dropping
• Brown, mushy roots
• Soft or rotting stems
• Seedlings collapse at soil level

How to Identify

Check the soil and gently expose a few roots. Healthy roots are usually firm and pale; rotting roots are often brown or black, soft, and easily broken. Their outer layer may slip off when pulled. Look for persistent wetness, poor drainage, or decay at the stem base. Wilting from drought can look similar, but drought-stressed plants generally have dry soil and intact roots. Nutrient deficiencies may yellow leaves without making roots mushy. Waterlogging alone can also injure roots, so appearance cannot reliably identify a pathogen. If the cause matters for a valuable plant or a recurring outbreak, send a sample to a plant diagnostic laboratory.

Prevention

Grow plants in soil or potting mix that drains well, and use containers with drainage holes. Water according to the plant’s needs and the moisture below the surface rather than on a fixed schedule; empty saucers after watering. Avoid planting in low spots where water stands, and improve compacted soil or use raised beds where appropriate. Do not bury stems deeper than recommended or crowd plants so tightly that the soil stays damp. Start with healthy plants and clean potting mix, and clean tools and reused pots before moving between plants. Remove badly diseased plants and avoid moving contaminated soil to other beds. Choose resistant varieties when available, especially where a particular root-rot pathogen has been identified.

Treatment

First, correct the conditions that are keeping roots wet: reduce watering, clear blocked drainage, and let the soil dry to a level the plant tolerates. For a container plant caught early, remove it from the pot, discard the old mix, and trim away clearly soft, dead roots with clean tools. Repot in fresh, well-draining mix in a clean container. Keep the recovering plant out of harsh sun and water carefully; damaged roots need time to regrow. Do not cut away so many firm roots that the plant cannot survive. Remove and discard plants with extensive root or stem-base decay; they seldom recover. Avoid replanting a susceptible plant immediately into the same affected soil. Fungicides are a last resort and will not restore dead roots. Use one only if the pathogen has been identified, the product is labeled for that plant and disease, and its directions can be followed. Treatments for Phytophthora or Pythium may differ from those for true fungi.

Plants Affected

Abelia, Adzuki Bean, Alder, Aloe Vera, Amaryllis, American Chestnut, Anthurium, Arborvitae, Arrowroot, Aucuba, Australian Sandalwood, Azalea, Banyan, Baobab, Bay Leaf, Beech, Bird of Paradise, Blue Gum, Bluebeard, Bluebell, Blueberry, Bluebonnet, Boxwood, Bristlecone Pine, Broom, Butterfly Bush, Buxus, California Poppy, Callicarpa, Camellia, Cannellini Bean, Caryopteris, Cassava, Ceanothus, Cedar, Chestnut, Chickpea, Chinese Chestnut, Choisya, Christmas Cactus, Cistus, Cleyera, Coconut Palm, Coneflower, Coreopsis, Cork Arborvitae, Cork Bristlecone Pine, Cork Cedar, Cork Cypress, Cork Fir, Cork Hemlock, Cork Juniper, Cork Kauri, Cork Larch, Cork Monkey Puzzle, Cork Oak, Cork Pine, Cork Redwood, Cork Sequoia, Cork Spruce, Cork Yew, Corpse Flower, Crocus, Crown of Thorns, Curry Leaf, Cypress, Daffodil, Daphne, Desert Rose, Douglas Fir, Drumstick, Echeveria, Edamame, Elaeagnus, Enkianthus, Escallonia, Eucalyptus, European Chestnut, Fir, Fothergilla, Frangipani, Galangal, Gardenia, Garlic, Gaultheria, Ghost Orchid, Ginger, Ginkgo, Ginkgo Biloba, Griselinia, Guar Bean, Heath, Heather, Hebe, Heliconia, Hemlock, Holly, Holm Oak, Horse Gram, Hyacinth, Ilex, Impatiens, Indian Rubber Tree, Indian Sandalwood, Iris, Jacaranda, Jade Vine, Juniper, Kadupul Flower, Kaffir Lime Leaf, Kalmia, Kauri, Kidney Bean, Laurel Oak, Lavender, Lavender Cotton, Lemongrass, Lentil, Leucothoe, Ligustrum, Lima Bean, Live Oak, Lotus, Lotus Root, Lupine, Magnolia, Malanga, Marjoram, Middlemist Red, Monkey Puzzle, Moth Bean, Mountain Laurel, Myrica, Myrtle, Nandina, Oil Palm, Orange, Orchid, Orchid Cactus, Oregano, Osmanthus, Palm, Parrot Flower, Passionflower, Pea, Pieris, Pine, Pineapple, Pinto Bean, Pittosporum, Plumeria, Potentilla, Purslane, Redwood, Rhododendron, Rockrose, Rosemary, Rubus, Ruscus, Sacred Fig, Sage, Sago Palm, Sandalwood, Santolina, Sarcococca, Savory, Sequoia, Shasta Daisy, Skimmia, Snap Pea, Snowdrop, Southern Magnolia, Soybean, Spruce, St. John's Wort, Statice, Tamarind, Tamarix, Taro, Tarragon, Tasmanian Blue Gum, Taxus, Tepary Bean, Teucrium, Thuja, Thyme, Tulip, Turmeric, Ulex, Vaccinium, Vitex, Weeping Fig, Windmill Palm, Wisteria, Xanthoceras, Yam, Yew, Yucca, Zenobia

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