MSc

The present investigation ‘Studies on the control of soft rot of ginger’ was conducted at the Instructional Farm, attached to College of Horticulture, Vellanikkara, Trichur during the year 1978-79. Two varieties of ginger viz. ‘Rio-de-janeiro’ and ‘Maran’ were used for the investigations.
The objectives of the investigations were 1) to find out the causal organism of soft rot of ginger in the acid lateritic soils of Vellanikkara 2) to find out suitable control measures against the disease 3) to know whether the fungus could develop resistance against continuous application of fungicides and 4) to find out any adverse effect on the development of ginger rhizomes when the fungicides were applied for controlling the disease.
The pathogen responsible for the disease was found to be Pythium aphanidermatum (Edson) Fitzpatrick. More than 90 per cent inhibition of the fungus was observed by agallol, thiride and difolatan at 500 ppm concentration in vitro. Hundred per cent inhibition of the fungus was possible only with 2000 ppm of Cheshunt compound or thiride and with 500 ppm of agallol in vitro. Among the different combinations of Cheshunt compound, agallol and thiride, 100 ppm of agallol plus 100 ppm of thiride was the most effective combination in inhibiting the mycelial growth of the fungus.
Seed treatment with 0.25 per cent agallol solution alone was not effective in reducing the disease incidence in the field. The fungicides which were proved very effective in in vitro studies, were again tested under field conditions. They were Cheshunt compound, agallol and thiride. Soil drenching before planting with the above mentioned fungicides reduced the pre emergence rotting considerably. Single application of fungicides either in one, three or four months after planting was not adequate in controlling the disease.
A minimum of two post emergence applications i.e. One month and three months after planting either with cheshunt compound or agallol, in addition to pre planting soil drenching were necessary for controlling the disease as well as for getting good yield. P. aphanidermatum did not develop any resistance against the fungicides when they were applied continuously in the field. Adverse effect on the development of ginger rhizomes was not noticed when the fungicides were applied for controlling the soft rot of ginger.
The present investigation showed that extent of control varied with the sequence and number of fungicidal applications. Treatments agallol – cheshunt compound, cheshunt compound – cheshunt compound and cheshunt compound – agallol in two times application; cheshunt compound – cheshunt compound – cheshunt compound ; cheshunt compound – agallol – thiride and cheshunt compound – thiride – agallol in three times application and cheshunt compound – cheshunt compound – cheshunt compound – cheshunt compound; agallol – agallol – agallol – agallol and cheshunt compound – thiride – agallol – cheshunt compound in four times application showed a better disease reduction compared to other treatments.
The post emergence rotting started appearing from July and peak infection was noticed during August. The variety ‘Maran’ was more resistant to the disease. There was a direct correlation between the disease incidence and continuous rainfall.