Cabbage Integrated Pest Management : An Ecological Guide.

Major Diseases of Cabbage¤Points to remember about soft rot:1. Soft rot bacteria survive in soil on decaying and dead plant debris2. Wounds in plant tissue are entry points for soft rot bacteria.3. Avoiding crop injury and good sanitation practices (removing infected material) are ways toreduce spread of soft rot disease.8.4 Bottom rot – Rhizoctonia solaniSee plate 2 Fig. 8Other names: wirestem (seedlings) and head rot.Causal agent: fungus – Rhizoctonia solaniThis fungus is also a common cause of damping-off in seedbeds (see section 8.1 above). This sectiondescribes the disease as it occurs in the main field.Subspecies of Rhizoctonia solani can cause diseases in many crops: stem cancer and black scurf ofpotato, root rot of cotton and many others.Signs and symptomsBottom rot develops on plants after they have been transplanted to the field. Dark slightly sunken spotsdevelop on basal leaves near the soil. Affected plants are weak, produce small heads and sometimes wiltand die. In moist conditions and in storage, rot spreads to adjacent leaves and causes a head rot. Thewhole cabbage head may develop a dry rot, first restricted to the outer wrapping leaves. Tiny sclerotia(fungus reproductive structures) which are irregular and brown in color may form on the rot.Diseased plants appear in patches in the field, with the location and size depending on weather and soilconditions. If a field has symptoms of root rot, the plants that survive are probably also damaged and mayhave lower yield or show disease symptoms when stressed later in the season.Source and spreadThe fungus Rhizoctonia solan is a common inhabitant of field soils. It can survive on decaying and deadorganic matter in the soil.Bottom rot (and damping-off) occur in areas with poor drainage or areas with a previous history of thedisease.Role of environmental factorsDisease is promoted by moist conditions and high soil temperature. Root damage from salts and soilcompaction can also lead to increased loss due to root rots.Natural enemies/antagonistsUse of the beneficial fungus Trichoderma sp. has been reported to prevent or cure soil-borne diseasesincluding root rots. There are several species of Trichoderma. The species Trichoderma harzianum hasbeen used successfully in tropical climates but Trichoderma parceramosum also gave good results infield trials in Philippines (FAO-ICP progress report ’96 – ’99). In Thailand and Indonesia, for example,Trichoderma is available for use by farmers. There are more details on Trichoderma in section 7.10.1.There are several other antagonistic organisms, including bacteria (e.g. Bacillus subtilis, Pseudomonas159 Cabbage Ecological Guide - 2000