Restoring Ibo Coco Via Fungicide

A research conducted at the University of Dschang during the 2012 cropping season has demonstrated that the disease, which hit the Colocasia esculenta (Ibo coco) in the South West Region and other parts of the country, some four years ago, can be mitigated through the monthly application of fungicide.

The research dubbed “Technical and economic evaluation of fungicide application on taro (Colocasia esculenta) blight” was jointly conducted by Dr. Takumbo, Dr. Fontem, Dr. Tarla Divine et al.

The researchers used a split-plot design whereby one plot had treated Ibo coco with fungicide and the other plot remained untreated. Sub-plots were assigned to two species of Ibo coco; the dark green stem commonly referred to as Ibo coco and the light green stem small leaves seeds also known as “Ehkoueh’lah”.

The soil was ploughed to a depth of 30 cm and Ibo coco seeds were planted on March 20, 2012. Poultry manure was applied a day before planting, while the second poultry manure application was done three months after. The manure was spread round the plant. Mineral fertilizer (NPK 12:11:18 +2.7MgO+8S) was also applied three months after planting. The field was weeded both manually and chemically. Corms were harvested on November 4 and December 4, 2012 (7.5 and 8.5 months after planting) for the Ibo coco and the Ehkoueh’lah cultivars respectively, when most of the leaves had dried off.

The research demonstrated that the Ibo coco disease, which leaves dark spots on the leaves and makes Ibo coco tubers rotten, was more severe in the unsprayed plots. Amongst the seeds, Ibo coco was more vulnerable to taro blight disease.  The plots which were sprayed had their final disease below 25%. This implies that fungicide reduced the growth rate of the Ibo coco disease up to the extent that the severity of the disease could not go above 25% before harvest. Thus, it can be concluded that Plantomil 72 WP (metalaxyl and copper II oxide) greatly reduced the severity of taro blight, even when applied at monthly intervals. On the other hand, leaf losses of up to 93% were recorded in unsprayed plots of the Ibo coco.

The research demonstrated that the quantity of Ibo coco harvested was higher in the sprayed plot than in the unsprayed plot. Ibo coco yields were just 16.11t/ha in control plots where fungicide was not used and between 60.44 – 62.1t/ha in sprayed plots. The high difference in yields between sprayed and unsprayed plots was due to a high taro blight severity in unsprayed plots, which greatly reduced the number and surface area of functional leaves, hence, a reduction in photosynthesis. The disease equally resulted in smaller tubers in unsprayed plots whereas the sprayed plot had bigger tubers.

An economic analysis revealed that there were high returns in plots sprayed at weekly intervals. Net benefit was rather higher 8.27 million frs cfa in “Ibo coco” plots sprayed once every month and 4.81 million frs cfa in “Ehkoueh’lah” plots sprayed once every two weeks.

Based only on net benefit, a monthly spray interval and a two-week sprayed interval could be adopted for the control of the disease on the “Ibo coco” because these spray intervals yielded high revenue. The research demonstrated that every franc spent in protecting the crop was recovered 13.78 times for “Ibo coco”.  

From the research, it was concluded that the Ibo coco disease is a yield-limiting constraint in the production of the crop in Cameroon. This is supported by high yield increases of up to 74.06%, observed in sprayed plots of Ibo coco. It was also concluded that fungicide applied at the rate of 3.33kg/ha significantly reduced taro blight severity in Ibo coco.

Ehkoueh’lah, seeds are more tolerant to taro blight compared to the “Ibo coco. Economically, the monthly fungicide spray schedule gave high returns for “Ibo coco” and “Ehkoueh’lah” respectively. This implies that applying fungicide against taro blight is the profitability of this fungicide.

About the disease

Taro leaf blight caused by Phytophthora colocasiae Raciborski is the most destructive fungal disease responsible for heavy yield losses of Ibo coco in many countries. In addition, this pathogen causes a serious post-harvest decay of Ibo coco tubers. In Africa, taro leaf blight was first reported in Ethiopia and Equatorial Guinea in 2005. It arrived in Nigeria in 2009 and in Cameroon in 2010. In Cameroon, the disease caused many farmers to abandon their fields.

The research paper explains that relying on the removal of all leaves with lesions as a method of control would quickly lead to a complete defoliation of the crop with consequent effects on yield. With the above weaknesses, the cultural method and the use of resistance varieties cannot control the disease satisfactorily to provide enough tubers needed by the fast growing population.

The research, therefore, suggests the use of an integrated disease management strategy which seeks to protect the environment may be of importance. Among these methods, the rational use of fungicides to control diseases is the fastest management method.

For farmers interested to adopt this method to improve on fight the Taro blight disease, contact the corresponding authors at tarladn@yahoo.fr and dfontem@yahoo.com