Damping off is the single term used to describe
underground, soil line, or crown rots of seedlings due to
unknown causes. The term actually covers several soil borne
diseases of plants and seed borne fungi. The fungi which
cause root rot are species of Phyium, Phytophthora,
Rhizoctonia and Fusarium.
There are two types of damping off: pre-emergence and post-
emergence. In pre-emergence damping-off, seeds may rot and
seedlings may decay before they emerge. In post-emergence
damping off the seedlings emerge then may pale, curl, wilt,
and collapse from a rot at the soil line and below. The
base of the stem is generally water-soaked at first then
turns gray to brown or black then rots.
Vegetable seedlings often do not grow well under humid
conditions, particularly if the soil is cold and wet.
Damping off fungi flourish in moist, unhygienic conditions.
The disease often starts at one end of a seed tray, and
quickly spreads to the other end. A fluffy fungal growth
may also appear on the soil surface as well as on the dead
seedlings.
When preparing to plant be sure that flats, tools, plant
containers, and benches are clean. Damping off pathogens
can live in these containers. The easiest way to disinfect
them is to dip them in a bleach solution for 10 seconds.
Use 1 part bleach to 4 parts water. Or use 70 percent
rubbing alcohol.
Plant in a light, well drained fertile seedbed. Preferably
use sterile soils that have been pasteurized with heat
before planting. Maintain a soil pH at the low end of the
average scale. A soil of 6.4 pH is less susceptible to root
rot than a pH of 7.5. As plants are watered the pH
gradually increases. Test often and continue to maintain a
lower pH while the plants are still germinating. If
necessary use one tablespoon of vinegar to 1 gallon of water
to lower a rising pH level.
Plant seeds no deeper than 4 times their own thickness.
Keep the seedbed soil on the dry side after planting and
allow plenty of bright light but not direct sunlight.
Use plant containers with drainage holes, water from the
bottom only, and avoid excess watering. Do not allow pots
to stand in water as excess water cannot drain and the roots
will be starved for oxygen which will stop all growth of
seedlings. Never water late in the day.
Avoid overcrowding and overfeeding of plants. Do not
overfertilize, especially with nitrogen. |
