Seedling damping off and
By Daniel S. Egel, Extension Plant Pathologist
Southwest Purdue Agricultural Center,
Cold winds howl across the landscape today,
but it won’t
be long before gardeners will turn their attention to starting
transplants inside the house or in cold frames. These transplants
include all manner of flowers and vegetables destined for outside
gardens when the weather improves. Unfortunately, some of
those transplants will become diseased and die before making it
to the garden. Damping-off and root rot are two of the most
common diseases of seedlings of all types of plants.
Damping-off may cause seeds or seedlings to rot
prior to emergence through the soil (pre-emergence damping-off)
or cause a brown area on the stem of the seedling where the stem
(technically, the hypocotyl) contacts the soil (post-emergence
damping-off, Figure 1). Affected
stems may shrivel and become thin; ultimately the seedling will
fall over, that is, damp-off.
Root rots may be suspected if seedling
growth is slow and leaves and seed leaves (cotyledons) become yellow
muskmelon seedlings have been removed from the transplant tray
in Figure 2. The seedling on the right is a healthy green
and the white roots have completely filled the cell of the transplant
tray. In contrast, the seedling on the left is stunted, has
yellow leaves and discolored, rotted roots that have failed to
fill the transplant tray cell.
Both damping-off and root rot are caused
by a number of fungi which inhabit the soil (Pythium spp.
and Rhizoctonia solani are
two of the most common fungi involved). These fungi may infect
seedlings alone or in combination with other fungi. The fungi
responsible for these diseases may survive for long periods in
soils, soil mixes or even on contaminated tools, benches or transplant
Environmental conditions may also help
to worsen damping-off and root rot. Cool, wet soils favor damping-off and root rot. Another
factor that may aggravate damping-off is when seedlings become
long and thin (etiolated). Seedlings raised in low light
conditions tend to be long and thin because they are growing toward
light. Such seedlings are often very susceptible to damping-off.
Below find some ideas for managing damping-off and root rot of
Avoid bags of soil or soilless mixes that have been broken
open and store bags so that they do not come in contact with
water or contaminated soil.
Use only new or disinfected pots and trays
to grow transplants. To
disinfect used pots or trays, first clean these items so that
they are free of soil and debris. Then use a 10% bleach
solution or a quaternary ammonium solution as a disinfectant
and then rinse with clean water. Always use gloves and
Clean and disinfect all tools and bench
tops that come into contact with soil to be used with transplants.
Gardeners should avoid overwatering soils
and should make an effort to keep soils warm. Avoid soils or soilless mixes
that drain poorly. Outside gardens with raised beds increase
soil drainage and warmth.
As much as possible, gardeners should use
a light source that minimizes seedling stretch.
Click image to enlarge
Figure 1: This muskmelon seedling is discolored and withered
where the stem contacts the soil and will soon collapse or damp-off.
Figure 2: While the muskmelon seedling on the left has a healthy
green color and nice white roots, the seedling on the left suffers
from root rot.