The single term used to describe underground, soil line, or crown 
rots of seedlings due to unknown causes is damping-off . The term 
actually covers several soil borne diseases of plants and seed borne 
fungi. 

Rhizoctonia root rot (Rhizoctonia solani) is a fungal disease which 
causes damping-off of seedlings and foot rot of cuttings. Infection 
occurs in warm to hot temperatures and moderate moisture levels. 
The fungi is found in all natural soils and can survive 
indefinitely. Infected plants often have slightly sunken lesions on 
the stem at or below the soil line. Transfer of the fungi to the 
germination room or greenhouse is easily accomplished by using 
outdoor gardening tools inside or vice versa. The germination room 
should not be used for mixing potting soils or transplanting 
seedlings as a general rule. 

Pythium Root Rot (Pythium spp.) is similar to Rhizoctonia in that it 
causes damping-off of seedlings and foot rot of cuttings. However, 
infection occurs in cool, wet, poorly-drained soils, and by 
overwatering. Infection results in wet odorless rots. When severe, 
the lower portion of the stem can become slimy and black. Usually, 
the soft to slimy rotted outer portion of the root can be easily 
separated from the inner core. Species of Pythium can survive for 
several years in soil and plant refuse. 

Phytophthora root rot (Phytophthora spp.) are usually associated 
with root rots of established plants but are also involved in 
damping-off. These species enter the root tips and cause a water-
soaked brown to black rot similar to Pythium. These fungi survive 
indefinitely in soil and plant debris. 

Black root rot (Thielaviopsis basicola) is a problem of established 
plants. It does not occur in strongly acid soils with a pH of 4.5 
to 5.5. It usually infects the lateral roots where they just emerge 
from the taproot. The diseased area turns dark brown, and is quite 
dry. The fungi survive for 10 years or more in soil. 

Miscellaneous fungi causing similar symptoms include Sclerotinia 
(white mold), Sclerotium rolfsii, Macrophomina phaseoli, some 
species of Botrytis (gray mold), Aphonomyces, Fusarium, 
Cylindrocladium, and others. Hence the need for the collective term 
known as damping-off. 

Symptoms of Damping-off: 
Seeds may be infected as soon as moisture penetrates the seed coat 
or a bit later as the radicle begins to extend, all of which rot 
immediately under the soil surface (pre-emergence damping-off). This 
condition results in a poor, uneven stand of seedlings, often 
confused with low seed viability. Cotyledons may break the soil 
surface only to whither and die or healthy looking seedlings may 
suddenly fall over (post-emergence damping-off). Infection results 
in lesions at or below the soil line. The seedling will discolor or 
wilt suddenly, or simply collapse and die. Weak seedlings are 
especially susceptible to attack by one or more fungi when growing 
conditions are only slightly unfavorable. Damping-off is easily 
confused with plant injury caused by insect feeding, excessive 
fertilization, high levels of soluble salts, excessive heat or cold, 
excessive or insufficient soil moisture, or chemical toxicity in air 
or soil. 

Above ground symptoms of root rot include stunting, low vigor, or 
wilting on a warm day. Foliage of such plants may yellow and fall 
prematurely starting with the oldest leaves. The roots of a 
diseased plant will have some shade of brown or black and evidence 
of water-soaking. Healthy roots are fibrous appearing and are 
usually white or tan in color. These symptoms are easily confused 
with severe mite, aphid, scale infestations, or root-feeding by 
nematodes or insect larvae. Environmental factors such as 
accumulated salts in the soil, insufficient light or nitrogen, 
potbound roots, cold drafts, etc. can be eliminated only by 
examination of the roots. 

Damping-off diseases can be prevented: 
Purchase disease free plants and seeds. Know your supplier. Do not 
be afraid of fungicidal coatings on seeds which will be direct sown 
out doors in cold soils, such as corn and peas. Seed borne disease 
can also be avoided by soaking the seeds for 15 minutes in a bleach 
soak (one teaspoon per quart of water) prior to sowing. 
Use sterile well drained soil mediums. See article on soil mixes. 
Try to maintain a soil mix pH at the low end of the average scale, 
i.e. 6.4 pH is less susceptible to root rot than a pH of 7.5. 
Commercially prepared germination mixes usually have a pH around 
5.5. As you water the seed pots and your seedlings with tap water 
(which in many municipalities is quite alkaline), the pH in your 
pots gradually increases as does the susceptibility to damping-off 
diseases. Know the pH of your tap water, and condition it if 
necessary to maintain a lower pH while the plants are still in the 
germination room. I prefer the use of vinegar at the rate of one 
tablespoon per gallon of water. 
Plants must not have their crowns below the soil line. Seeds must 
not be covered more than 4 times the thickness of the seed. 
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 bringing all growth to a halt. 
Avoid overcrowding and overfeeding of plants. It is important to 
maintain constant levels of growth through proper lighting and 
complete control of the growing environment. 
Avoid working with plants (taking cuttings or transplanting) when 
the soil is wet. Do not use water from ditches or drainage ponds or 
rain barrels in the germination room. 
Avoid spreading soil from infested areas or tools which have been 
used out of doors. Disinfect tools and containers with one part 
bleach in four parts water or with 70 percent rubbing alcohol 
(isopropyl). 
In the germination room, sow all your seeds on the surface of the 
media, then cover the seeds to necessary depth with a material which 
is less likely to harbor fungi than the media itself. Use one or 
more of the following seed toppings instead of soil mix: 
milled sphagnum moss 
chick grit 
course sand or fine aquarium gravel 
composted hardwood bark (steamed) 
In the germination room, mist seedlings in communal pots or flats 
once or twice per day with water containing a known anti-fungal 
agent such as: 
Captan (or other approved fungicide) especially if walls or floors 
are damp, or 
Cheshunt compound, a copper/aluminum formulation, or 
chamomile tea, or 
clove tea, or 
a one-time light dusting of powdered cinnamon on the soil surface, 
or 
a one-time light dusting of powdered charcoal on the soil surface, 
or 
if stinging nettle is endemic in your area, make a fermented 
infusion to use like clove tea. These last five actions 
are suggested by sufficient anecdotal evidence to prove the 
existence of a low level of fungicidal activity. I would not 
hesitate to use them in germination environments which have no 
history of damping-off diseases. 
Rotate plantings on a 2 to 3 year schedule using plants from 
different families in order to starve out existing pathogens. 
Provide constant air movement not tied in with the light timer. Air 
should move freely 24 hours per day, but not directly aimed at the 
plants. This helps the seedlings to aspirate, and excess soil 
moisture to wick. If you do everything else right but do not 
provide plenty of air movement, you will still get damping-off. 
So, what do I do? Answer: all of the above, all of the time. 
Damping-off diseases can be controlled: 
Fungicides may be applied as a soil drench after planting. They may 
be incorporated into the soil before planting as a dust. They can 
be sprayed in mist form on all seedlings as a precaution until they 
have been transplanted into individual pots. Once transplanted, 
only those seedlings known to be especially sensitive to damping-off 
need be misted with fungicide daily until the first or second seed 
leaves have emerged. The following chemicals are not recommended 
for use by the average recreational gardener, but may still be 
available for use (if not yet banned), providing the manufacturer's 
instructions are followed to the letter. 

Captan (sold as Captan) controls most pathogens, but not 
Rhizoctonia. 

Metalaxyl (sold as Subdue or Apron) controls Pythium, Phytophthora, 
and Aphanomyces. 

Iprodione (sold as Chipco) controls most pathogens, but not Pythium, 
Phytophthora, or Aphanomyces. 

Etridiazole and Thiophanate-methyl (sold as Banrot) controls most 
all pathogens. 

PCNB-etridiazole (sold as SA-Terraclor or Super-X) good general 
purpose fungicide. 

PCNB-quintozene (sold as Terraclor, Fungi-clor, or PCNB) controls 
Rhizoctonia and Sclerotinia species. 

Fosetyl-A1 (sold as Aliette) controls Pythium, Phytophthora, & 
Aphanomyces. 

Well, you get the idea. There are too many to list, and they go on 
and off the market very quickly (mostly because they are very 
dangerous when used improperly, and some are too dangerous to have 
been put on the market at all.) 

So, what do I use? Answer: Just enough Captan as needed. 
The Future of Damping Off Control: 
Biocontrol with microbial fungicides is being investigated in 
several academic labs. Typical targets are those plants being mass-
produced in nearby commercial greenhouses. Early results indicate 
damping-off prevention comparable to that achieved with the use of 
standard fungicidal drenches like those mentioned above. However, 
there remain some notable drawbacks in biocontrol of damping-off. 

First, microbial fungicides act against only one species of root or 
stem rot, and must be applied in advance. So, in order to prevent 
damping-off, you must know in advance which species of Pythium or 
Rhizoctonia or other fungi is likely to attack your crop. That 
limits their use to large production facilities. 

Second, some formulations of microbial fungicides have been shown to 
produce substances that are phytotoxic to certain crops. 

Finally, small changes in environmental conditions during test 
periods seem to cause significant differences in test results


