I wrote a few weeks ago about it being time to start your cool weather seeds. Soon it will be time to start tomatoes, peppers and a variety of different flowers. If you are going to be starting plants from seed one thing to be on the look-out for is damping off.
Damping off is a fungal disease that can be cause by several different soil-borne fungi. It is most commonly caused by Fusarium spp., Pythium spp., and Rhizoctonia spp. It affects a wide variety of plants. It is a disease of seedlings, once plants produce mature leaves and have a well-developed root system they are in the clear. Plants infected with one of these pathogens may never emerge from the soil (just because a plant never comes up doesn’t mean it’s infected, not all seeds will germinate) or they may develop dark, sunken tissues at the base of the stem (where it meets the soil). These plants will then fall over and eventually die. An infection can spread through the soil and eventually infect an entire tray of seedlings.
The best way to deal with damping off is to avoid it altogether, this is done by proper sanitation and providing the proper growing environment for seedlings. The pathogens that cause damping off survive on plant debris, soil or contaminated planting equipment (pots, trays, tools, etc). This is why it is important if you are reusing pots and trays from previous years to disinfect them (soak in a 10% bleach solution for at least 20 min) and why you shouldn’t use garden soil (it will often contain the pathogens). It is also a good idea to disinfect tools and work benches with a 70% alcohol solution.
Make sure to plant your seeds at the proper depth (as indicated on the seed packet), seeds that are planted to deep are more susceptible to infection. The fungi that cause damping off enjoy cool, moist environments. Make sure your seed starting media is moist, not soggy. When starting plants that need warm soil to germinate (such as tomatoes and peppers) use a heating mat if starting them in a cool area like a basement. Plants grown at warmer temperatures will grow out of their susceptible phase much quicker than plants grown in cooler conditions. When watering plants don’t use cold water, use lukewarm or room temperature water. Cold water will slow the growth of the plant as well as cool the soil down which will favor development of the disease. Also make sure that plants are getting adequate light. Plants that are tall, thin and weak (like plants growing under low light or over fertilized with nitrogen) are more susceptible to damping off.
If you have seedlings that become infected they should be removed immediately and discarded. If have had problems with damping off in the past you may want to plant seeds treated with thiram or captan.