Damping off, Symptoms and management
The single term to describe underground, soil-borne, or crown rots of seedlings due to syndrome complex of soil-borne fungi is known as damping off. The term covers several soil-borne diseases of plants and seed-borne fungi.
- It is the major problem of the nursery, seedbed, or of the home vegetable garden.
- Fungi in soil attack seed and seedlings as they begin to germinate and grow.
Rhizoctoinia root rot: Rhizoctonia solani
Cause damping-off of seedling and root rot of cuttings. Infection occurs in warm to hot temperatures and moderate moisture levels.
Pythium root rot: Pythium sps
Same but occur in cool, wet, poorly drained soils and by overwintering. Infection results in wet odorless rots. When severe, the lower portion of the stem can become slimy and black.
Phytophthora root rot: Phytophthora sps
These sps are usually associated with root rots of established plants but also involved in damping off. Species enter the root tips and cause water-soaked brown to black rot similar to Pythium. Fungi survive indefinitely in soil or plant debris.
Black root rot: Thielaviopsis bacicola
It is a problem of established plants. It does not affect in strong acid soil pH 4.5 to5.5. Usually, affects lateral roots where they just emerge from taproot. Fungi survive for 10 years or more in soil.
White mold (sclerotinia rot): Sclerotinia rolfsii, Macrophomina phaseoli
Botrytis(grey mold): Botrytis, Fusarium
Systematic position: Class: Oomycetes Order: Peronosporales Family: Pythiaceae
Pre-emergence damping off:
When the seed or seedling dies before it reaches the surface. Seedling is killed before hypocotyl has broken the seed coat or if radical and plumule come out of the seed they undergo complete rotting thus results in poor stand.
Post-emergence damping off:
When the seedling emerges and grows to a height of an inch, then wilts and dies.
- Infection results in lesions at or below the soil
- Seedling will discolor or wilt suddenly or simply collapse and
- Weak seedlings are especially susceptible to attack by one or more fungi when growing conditions are only slightly unfavorable.
- Damping off is confused with plant injury caused by insect feeding, excessive fertilization, high level of soluble salts, excessive heat or cold, excessive or insufficient soil moisture or chemical toxicity in the
- Above ground symptoms of root rot include stunting or wilting on a warm
- Foliage of such plants may be yellow and fall prematurely starting with the older
- The roots of disease plants will have some shade or brown or black lesions and evidence of water soaking
Disease cycle and epidemiology:
Pythium is a weak saprophyte and poor parasite. Survival structures on soil or plant debris are sporangia and oospores. Oospores formed by fertilization of oogonium and antheridium germinate by the formation of germ tube and penetrate the cell wall of hypocotyl and incite primary infection. Sporangium upon germination, zoospores are formed which are biflagellate and germinate by producing a germ tube and start a secondary infection
- Disease more problems in ill drained soil, clay, heavy, compact soil
- The disease is more serious at 24-300c and high soil moisture accelerates diseases
- The disease spread with the help of water, rain splashes
- Collect seed from disease-free plants
- Use sterilized soil, a pH of soil 6.4 is less susceptible to root rot than 7.5.
- Do not cover the seed more than four times the thickness of the seed
- Avoid over-crowding and over-feeding of plants.
- Avoid working in plants when soil is wet.
- Plant when the temperature is favorable for rapid seedling growth.
- Reduce waterlogging, use raised beds.
- Thinning of plants to improve air circulation.
- Do not over-fertilize with nitrogen
- Crop rotation.
- Soil treatment with 2.5% formalin solution fortnight before sowing.
- Hot water treatment of seed.
- Application of Biocare-B, Biocare-F@ 2gm/lit spray or 5 kg/ha mixed with organic soil first allowing it to grow and application in the field.
- Use of seed protectants 2gm/kg captan, thiram, carbendazim to avoid pre-emergence damping off.