Dealing with Damping Off
So you've got "damping off" and want a quick fix... NOW:
Put trays in a light*, well aired (but not draughty) area. Water thoroughly with a fungicide (eg. "Previcur N" (propamocarb) "Terrazole" (etridiazole/xyl ene) against pythium and phytophthera, and/or "Rizolex" (tolclofos- methyl) against rhizactonia (check the chemical names, in brackets on the fungicide packets, if the trade names, in parentheses, are not in your store) or try chamomile tea... it may work.
Damping off is a problem that many amateurs, and too many professionals, tend not to handle very well, probably because they don't understand what they are dealing with.
Damping Off is a generic term for all those diseases which kill the new seedling upon, or shortly after emergence, and is usually caused by either or all of the following pathogens:- phytophthera, pythium or rhizoctonia.
These three vandals often work in concert and are all "water moulds". That is they live in and are transported by water. They are thus easily transported from one place to another by water splashes, in soil, on equipment etc. and will readily carry over from seed trays used last time, or last season, unless these are treated in some way that kills them. We find the easiest way to do this is to wash (plastic) or soak (wooden) flats with "Jeye's" fluid (directions on the bottle) or some other similar product. This kills the pathogens, is cheap, easy to do and safe to both plants and humans. Do the same to benches that you place your flats on.
It is also a good idea to cover your bench, which should be high enough to prevent water splashes from the ground, with new, thin (30 - 50 micron) black plastic. The mulch plastic you may be able to obtain from garden centres is ideal. This provides a protective barrier against any disease still left below (water moulds can "swim" up into your flats).
Once you have a clean bench and tray (flat) don't contaminate it with unclean soil, mix or equipment (hands included). After we have our trays and mix and seed ready we wash our hands, just in case, before handling the seed.
Water with clean water. Avoid using water collected from the roof and taken from a barrel at the bottom of your downpipe. Using this water (without first boiling it) may re-introduce disease. Chlorinated house water is fine.
So the first step is "Hygiene". The second step is "Hygiene", as is the third. This is very important and well worth the time it takes. Any compromise will have results which will have to be dealt with later.
Having prepared your propagation room, which is of course in a place which allows maximum light and is well vented (to prevent disease and high temperatures) and sanitised as above, you may as well sow the seed.
Whatever mix you use to sow your seed in it should retain moisture while being well aerated and pathogen free. Some seed sowing mixes available "off the shelf" are none of these. You will have your own pet mixes but a 60/40 peat/pumice ratio suits very well, John Innes mixes or UC (University of California) soil- less mixes are great. Above all, avoid mixes that waterlog easily.
Sow the seed thinly. Sowing too thickly encourages damping off diseases in the young seedlings by preventing good aeration and allowing moisture to spread disease. Don't cover seed too deeply and thickly. It is common to see the whole surface of the mix in the flat raise up as seeds germinate. This is called bridging... if this happens water heavily to break the "bridge" and allow to dry off again.
Moisture is critical. If seeds dry out after absorbing water they may die. Too much moisture may suffocate seedlings and encourage root rots. Watering must be uniform but not excessive and above all.... avoid watering in the evenings when excess moisture does not dry off.
Air and media temperature should generally be in the range..15-25 degrees centigrade (60-75deg F). Unthermostatted heat beds may cause excessive heating, as will unshaded, glass covered flats. This will kill seed or induce secondary dormancy. Cooler temperatures may inhibit germination. Soil temperatures in flats may frequently be 4-7 degrees F below air temperatures due to evaporation.
Ants, mice, slugs, cicadas, fungus gnats etc can cause major damage. Take whatever measures you are comfortable with to rid yourself of these pests.
Is the seed fresh or from a trusted source? Some seeds go off quickly, eg. delphinium. If you chill your seed a week before sowing it could well result in a more even and reliable germination. Check for special requirements, temp, stratification etc.. Some seeds are not compatible with certain fungicides.Take care to read the directions on the fungicide ... and seed.. packets