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Damping-Off

Damping-Off

Pythium aphanidermatum

fungi

In a Nutshell

    In pre-emergence damping-off, the fungus colonizes the seeds and hinders germinationThe seedlings that manage to take root grow poorly and are likely to topple down (post-emergence rot)Infections at later stages of plant growth result in the appearance of dark brown, slimy patches at the base of the stem

Hosts: %1$s

· Papaya

Symptoms

The fungus can affect papaya during all growth stages but it prefers to attack seeds and young plants. In pre-emergence of damping-off, the fungus colonizes the seeds and hinders germination. The seedlings that manage to take root only grow poorly (post-emergence rot). The rotting of root and stem tissues can cause them to topple down and die. Infections at later stages of plant growth result in the appearance of brown, water-soaked patches at the base of the stem. In severe cases, these patches enlarge and surround the stem, causing the tissues to become slimy, and turn dark brown or black (stem rotting). Leaves can become chlorotic, wilt and fall off. Defoliation leads to stunted plant growth and shriveled and malformed fruits.

Trigger

The disease is caused by the soil-borne fungus Pythium aphanidermatum. It can survive for several years in soil and plant residues. It preferably attacks seeds or young seedlings. It is disseminated via contaminated irrigation water, splashing rain or heavy rainfall. Stressful conditions, such as water flooding, excessive nitrogen application or overcrowding, weaken the plants and favor the development of the disease. Cool, moist, poorly-drained soils and warm temperatures are also favorable for pathogen growth. During rainy seasons, the infection can be severe. Especially moist soils are favorable for the fungus. When all the favorable conditions are met, it can be a severe disease of papaya.

Biological Control

Bio-fungicides based on the fungi Trichoderma viride, Beauveria bassiana or the bacteria Pseudomonas fluorescens and Bacillus subtilis can be applied around the root zone at the time of planting. These can be used as seed treatments as well. Plant extracts of Eupatorium cannabinum completely inhibit the growth of the fungus. Irrigation with "smoke-water" that can be generated by burning plant material and dissolving the smoke in water, apparently has an effect on the life cycle of the fungus, too.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. The soil or the base of the plant can be drenched with copper oxychloride or captan every fortnight from the time of planting. Alternatively, propamocarb, furalaxyl or metalaxyl-M can be applied on trees during fruit formation. Copper oxychloride or Bordeaux paste can also be applied to plants parts that have been pruned. Household bleach can be used to clean contaminated tools, pots and trays.

Preventive Measures

    Use seeds from healthy plants or from a certified sourceUse resistant varieties if availableKeep a minimum space between seedlingsAvoid deep planting of seedsThoroughly disinfect tools and equipmentUse sterile soils for raising the seedlingsAvoid contact with sources of contaminationPlant in well-drained soil and avoid excessive irrigationAvoid excessive nitrogen fertilizationRotate with non-host plantsAdopt the ring method of irrigation so that the water does not come in direct contact with the stemExpose the soil or seedbeds to solar radiation with a plastic mulch