Damp-off of Seedlings
by Fred Davis, MG, Hill Gardens of Maine (To view other previous articles, click Archives)
Welcome through Our Garden Gate! Soon, many of you will probably have vegetable and flower seedlings popping up all over the place. The average Maine home during early spring, however, is actually not the place where young plants really want to be. It's either too dry, too hot, too humid, too drafty, too bright, too dark - too something!
All these too's can, in some cases, make life miserable for seedlings and houseplants. In other cases they can make life end! For example, high humidity, higher than recommended temperature and decreased or absent air circulation provide a perfect set of circumstances for the encouragement of an annoyance called Damp-off. (Though most frequently experienced in seedling trays, damp-off can also infect and cause serious damage to softwood "tip" cuttings.)
Damp-off is actually a tiny fungus with the imposing name of Rhizoctonia and accomplishes its sordid task without warning and with alarming suddenness.
Stems of young seedlings become narrow and quickly turn black at the soil line and simply topple over. Once that damage is done, salvage of the infected plants is impossible.
Infection usually begins in a small, isolated spot, involving a few tiny plants but, if allowed, will spread rapidly to involve all seedlings in the container.
Being a fungus, spores (a little like seeds) can remain viable from one season to another in residues on unwashed pots, flats and seedling trays. Spores can also be transferred from one spot to another in the air and on contaminated tools, gloves or hands.
Immediate attention at the very first sign of infection is critical. Scoop out all affected plants and a generous amount of soil, and burn it. Never put the infected material in a compost pile or toss it into the garden.
There are several products you can use to treat damp-off in its early stages, including chemical fungicides (which I don't recommend). Saferís Insecticidal Soap markets a more natural treatment which works well. If you're watching your pennies, however, very finely powdered charcoal dusted on the soil surface is usually quite effective. Some gardeners have success using a light dusting of powdered sulfur.
A surprise came recently when researchers found that Trichoderma, a fungus found in compost and some finely shredded bark, is so active and aggressive that it out-competes Rhizoctonia. Seeding mixes with 40-50% compost or bark have fewer problems with damp-off.
Some tips that will help you avoid the disappointment of damp-off are:
Use only sterilized soil or mix for starting seeds or rooting softwood cuttings.
Provide adequate drainage so soil remains only slightly moist, not drippy, soggy wet. Water only when the soil surface shows signs of drying, but well before seedlings begin to wilt.
Insure good ventilation of both seedlings and cuttings.
Don't make the mistake of assuming that all seeds need to be kept very warm in order to germinate. Seed companies know what the optimum temperature is and print that information on packets. Generally, most seeds do just fine at between 65 and about 72 degrees (F).
Remember that excessive warmth, too much water, poor circulation and low light levels create the ideal environment for problems with damp-off.
Sow seeds thinly. Dumping in far too many seeds causes over-crowding, leaving tender young seedlings without adequate ventilation, and competing for light, water and nutrition, - thatís really asking for trouble.
Clean your hands, tools, fingernails, containers and work area! Sanitation is clearly one of the best ways to prevent this very serious problem.
Keep records of what you did, when you did it and resulting effects. You'll be much better armed to deal with this or similar maladies the next time they occur.
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