Damping off on Plants

Symptoms

A plant with damping-off can fail before you ever see it break the soil. The entire seed can decay before it even germinates. If the seedling does sprout, it often rots just below the soil line. That collapse happens at the soil line, and damp conditions make it worse. Older, more established plants are less likely to die from the same infection. Instead, they tend to develop rots in the stem and in the roots. Pull a struggling plant and look closely at its roots. Infected roots turn soft and mushy instead of firm. They also darken and look decayed rather than healthy and white. Spinach, tomato and alfalfa seedlings are among the plants that show this damage. Seeds and seedlings of these crops are vulnerable to the same soil pathogens. Wet soil keeps conditions right for this kind of damage to spread. Crowded flats and seedbeds give the problem more room to move between plants. Checking for these signs early can tell you whether the plant is affected.

Causes

Several soil fungi and fungus-like organisms cause damping-off. Pythium species are a common cause of this disease. Rhizoctonia species can also cause damping-off in seedlings. Fusarium species are another cause of the same disease. These pathogens thrive when the soil stays excessively wet. Overhead misting adds to that excess moisture around young seedlings. Low soil temperatures before germination give the pathogens an opening. High soil temperatures after seedlings emerge can trigger an attack too. Overcrowded flats and seedbeds let the disease move from plant to plant. Wet soil conditions favor these pathogens at every stage of growth. Tomato, spinach and alfalfa seedlings all face these same soil-borne threats. Spinach seedlings in particular show this damping-off when Pythium is present in the soil. Alfalfa seedlings face damping-off from Pythium both before and after they break through the soil. These are the organisms and conditions behind the disease.

Diagnosis

Seeds that never break the soil surface may already have decayed inside the ground. A seedling that collapses right at the soil line points to the same disease. Pull up a struggling plant and look at the roots for a diagnosis. Soft, mushy and darkened roots confirm the same soil-borne rot. An older plant with stem and root rot, instead of sudden death, fits this pattern too. Damp soil around the collapsed seedling supports this diagnosis as well. Low soil temperatures before germination or high temperatures right after emergence point to the same cause. Crowded flats or seedbeds raise the odds that this is what you are seeing. Wet soil conditions that favor these pathogens are another clue to check for. A healthy plant should show white, firm roots instead of this damage. Tomato, spinach and alfalfa seedlings are the plants most often checked for this problem. Checking soil temperature can help, since both low temperatures before germination and high temperatures after emergence are linked to the disease. Crowded seedbeds are worth checking too, since overcrowding is itself one of the causes.

Treatments

Wait until outdoor soil and air temperatures warm up before you plant. Set seeds at the proper depth, about twice the width of the seed itself. Disinfect any reused seedling flats and containers with a bleach solution before reuse. Start seedlings in a seed-starting mix that has been steam sterilized or pasteurized. Solarize outdoor soil during a fallow period to cut down on soilborne pests. Prepare your planting site well ahead of the day you actually plant. Solarizing the soil before planting also reduces Pythium and Rhizoctonia fungi directly. Start seeds and cuttings in pasteurized soil or a soilless mix and use only sterile flats or pots. Supply bottom heat so container soil stays between 70-75°F (22-24°C). Keep soil moisture even during germination and through early seedling growth, rather than letting it swing from wet to dry. You can also buy fungicide-treated seed or treat seed with a fungicide before you sow it. Most of these steps are cultural, changing conditions rather than using a chemical. Treating seed with a fungicide is the one chemical option in this list. These steps protect tomato, spinach and alfalfa seedlings from the same soilborne attack. A bleach solution is enough to disinfect flats and containers you plan to reuse. Solarizing your soil during a fallow period is one option for outdoor beds. Preparing your planting site ahead of time is one of the simplest cultural steps.

Prevention

Most cases of damping-off start with conditions you can avoid from the beginning. Keep soil moisture steady during germination instead of letting it swing from wet to dry. Wait for the soil and air to warm up before you plant outdoors. Start seeds in a pasteurized or sterilized seed-starting mix and use sterile pots. Avoid overcrowding your flats or seedbeds, since this is one of the causes of the disease. Low soil temperatures before germination and high temperatures right after emergence both raise the risk. Solarizing your garden soil during a fallow period also cuts down on these pathogens. Buying fungicide-treated seed gives you one more way to head off the problem. Excessive soil moisture and overhead misting are both listed as causes of this disease.

Plants most often affected

Tomato, spinach and alfalfa seedlings are among the plants that can develop damping-off disease. Spinach seedlings face this risk from Pythium when the soil stays damp. Alfalfa seedlings can develop damping-off both before and after they break through the soil.

• Coriander
• Fava Bean
• Field Pumpkin
• French Hydrangea
• Garden Cucumber
• Joshua Tree
• Kidney Bean
• Spinach