Seedlngs Damping Off

Clean pots and plenty of fresh air helps stop seedlings damping off

The first seeds have been sown. 

I’ve been staring at the seed packets for weeks next to the back door and decided they would have a better chance of growing if I actually put them in trays filled with compost. This isn’t always the case though as there are a LOT of things that would like to consume your valuable seeds.

For example, I planted peas and beans straight into the garden as they don’t really like being moved. The mice (or rats) digging them up didn’t care about moving them though. I’m not sure if rats and mice store food but if they do their pantry will be bursting full with my seeds. I have an emergency supply in case of a theft so all is good on that front. 

My broccoli, leaf salads, corgettes as well as a few sweet peas and sunflower seeds have gone under protection to save them from being munched by the night time visitors.

It’s not only things we can see that want a piece of the seeds. I’m cautious every year to keep the tunnel well ventilated come sowing and germinating time because a lack of air could cause the damping off disease we hear so much about in spring. 

At one time knowledgeable gardeners would recommend dousing the seeds/soil and sometimes yourself in something called Chestnut Compound to eradicate the problem. The main ingredient of the compound is copper sulphate and was used as a fungicide to control of powdery mildew, rust and blackspot on roses and rust and powdery mildews on other ornamentals and fruit and vegetables but like creosote- tar oils, green and yellow sulphur, paraquat, simazine, TBA and DDT , Chestnut Compound been banned from the garden centre shelves, so we need to look for simpler alternatives. Some folk are saying cinnamon powder works but to me that’s a bit like spraying  air freshener in a dirty room to mask the smell. The problem doesn’t go away.

Thankfully the best alternative doesn’t necessitate us diving into the kitchen cupboards or chemical shelf in the garage. 

It’s mainly a case of good hygiene practices.

What is Damping Off?

Damping off is a visible fungal growth on an emerging seedling. Infected seedlings rarely survive to produce a vigorous plant. Quite often a large section or an entire tray of seedlings is killed by damping off. Once plants have mature leaves and a well developed root system, they are better able to naturally resist the damping off pathogens. There is a critical period of growth between planting and maturity, where special care needs to be taken to protect sensitive seedlings.

A wide variety of vegetables and flowers can be affected by damping off. The fungi, Rhizoctonia, and Fusarium, along with the water mould Pythium, are the most common pathogens responsible for damping off.

How to spot

There are some key observations apart from the plants just keeling over and dying.

• The seedlings could fail to emerge from the soil.
• Cotyledons (the first leaves produced by a seedling) and seedling stems are water soaked, soft, mush and may be discoloured grey to brown.
• Seedling stems become water soaked and thin, almost thread like, where infected.
• Young leaves wilt and turn green grey to brown.
• Roots are absent, stunted or have greyish brown sunken spots.
• Fluffy white cobweb like growth on infected plant parts under high humidity.
• Mushy tan spots indicate infection by the damping off fungi on this overwatered seed tray.

Biology

All of the pathogens responsible for damping off survive well in soil and plant debris. They can be introduced into the seedling tray in several ways.

The pathogens can live on pots, tools, and potting media that have been used in previous seasons and are not properly cleaned. Spores of Fusarium can be blown into the production area, carried by insects like fungus gnats, or move in splashing irrigation water. Pythium. is often introduced on dirty hands, contaminated tools or by hose ends that have been in contact with soil and debris. Once introduced to a seedling tray, the damping off pathogens easily move from plant to plant by growing through the potting media or in shared irrigation water.

Garden soil often contains low populations of the damping off pathogens. If garden soil is used to fill seedling trays, the damping off pathogens are likely to be present and initiate disease in the warm wet conditions favourable for seed growth. Seeds that are directly seeded into the garden can also suffer from damping off. Disease is particularly severe in garden seedlings when seeds are planted in soils that are too cool for optimal germination or when weather turns cool and wet after planting resulting in slow germination and growth. Which I why I tend to put off seed sowing outside until the last minute

Prevention

• Sterilize all used pots and trays in a solution of 10% household bleach by soaking for 30 minutes.
• Use new potting media to fill trays. Do no reuse potting mix or use garden soil or compost.
• Clean all tools that will be used in planting and maintenance of the seedlings. Store them in a clean location when not in use.
• Use a heating pad under trays to warm soil to 70-75°F for indoor plant production.
• Wait until garden soil has reached optimal temperature for germination before planting outdoors. This temperature varies depending on the plant (Table 1).
• Use a potting media with good drainage. Water to keep potting media moist but not soggy. Use pots with drainage holes to insure good drainage of excess water.
• Keep hoses and water heads off the floor.
• Use clean tepid water to water young seedlings. Cold water slows plant growth and increases the opportunity for infection.
• Resist the urge to apply fertilizer to seedlings until several true leaves have developed. Then apply 1/4 strength standard soluble fertilizer. Many potting mixes contain slow release fertilizer and do not require any fertilizer application.