What is Damping Off?
Definition: ‘Damping off’ is a condition caused by pathogens that destroy seeds before germination or very young seedlings. The term refers to the outcome – weakened or dead seedlings or seeds. The seedling stem rots and the young plant collapses or seeds fail to germinate.
Is it really that serious? Yes, unfortunately! Damping off can affect up to 80% of seedlings. So, if affected, you could lose a significant number of plants. Research has found that “even a very low population density of soil-borne pathogens can lead to severe epidemic development.” (1)
What Causes Damping Off?
So, who are the little rotters responsible for this sad end to your plant ‘toddlers’ or seed ‘babies’?
There are over a dozen culprits of soil-borne disease-producing organisms – different species of fungi and fungus-like organisms called ‘oomycetes’. They live in soil and transfer to a seed or seedling when conditions are favourable. Some pathogens are carried inside seeds or on the seed coat. However, only a few are commonly associated with damping off.
Firstly, let’s meet a few pathogens and their tongue-twisting names! They include Pythium species, oomycetes like Rhizoctonia solani, Phytophthora, Fusarium and Aphanomyces cochlioides.
More importantly, where do they hang out? Wet or overwatered soil, particularly in cool temperatures or cloudy conditions, provides favourable conditions for oomycetes called ‘water moulds.’ Why? Clearly, because they require water to multiply and spread. Phytophthora and Pythium species are both parasitic oomycetes.
However, if you have warm, dry soil conditions, Rhizoctonia and Fusarium can thrive and are usually the most likely offenders. Rhizoctonia attacks seedlings causing them to collapse. A dry brown discoloured stem is often a clue.
This fungal pathogen thrives in soils with poor fertility (nutrient-deficient) and insufficient moisture. The brassica family of vegetables including broccoli, rocket, kale and cabbage seem most susceptible to this pathogen. Making your own seed raising mix just before sowing seeds may prevent this fungus from ‘priming’ itself to infect the emerging crop.
What are the Two Types of Damping Off?
Damping off affects both seeds and seedlings. So, what evidence should you look for?
- Pre-emergence: Seeds rot in the seed raising media before germinating or emerging above the soil level. Your seeds never appear to germinate. So, you may be left wondering what went wrong.
- Post-emergence: ‘Newborn’ seedlings that have recently germinated wilt, collapse quickly or die from soft rot in the stem. They usually fall over at the soil level. Woody seedlings may start to weaken and wither while still erect, but baby roots may decay soon after. The infected stem looks soft, brown and water-soaked. A bit of a sad story really, isn’t it? It’s devastating for new ‘plant parents’!