ABSTRACT
Black pod disease (BPD) is reputed for its regular occurrence in Africa and around the world with high propensity for massive destruction of cocoa pods in the field and total yield loss per season if proper management strategies are not applied. This research was designed to provide useful and timely information on BPD outbreak, its intensity and specific areas expected to be massively affected by the disease in Nigeria. Twelve (12) research locations were mapped out from four important cocoa producing states in Southwest, Nigeria for BPD assessment and forecast. The BPD forecast system “ETAPOD” accurately predicted BPD outbreak in Ondo (Ọwenà and Wáàsimi) and Osun (Adaàgbà, Iyánfá»wá»rá»gi, and Owódé-Igàngán), but it failed to give accurate predictions for Ogun (Ǫbáfémi-Owódé) and Oyo (Mòyè village, Dáagi-Lógbà and Olórò village) states. The performance of ETAPOD was greatly affected by the credibility of the data fed into the system, this can be improved on. ETAPOD predicted BPD outbreak closely within the range of natural BPD occurrences.
Key words: Disease forecast, black pod disease (BPD) outbreak, total yield loss, ETAPOD, data credibility.
Black pod disease (BPD) associated with symptoms like leaf blight, pod rot, stem canker and death of the entire Theobroma cacao plant was reported by Opoku et al. (2000) as one of the most influential diseases of cocoa. Akrofi (2015) reported that the disease occurred annually with high propensity for massive cocoa pod destruction and total yield loss if proper management strategies were not applied. Oluyole and Lawal (2008) reported an estimated average occurrence of the disease in several parts of West Africa as 40% and up to 90% in certain places in Nigeria. The extent of damage caused by BPD infections had been reported by Kudjordjie (2015) to be more in West Africa than in any other cocoa growing regions of the world.
This research was designed to provide useful and timely information on BPD outbreak, its intensity and specific areas expected to be greatly affected by the disease in Nigeria. This will eradicate doubts and uncertainty in the minds of investors on their choice of investment(s) made in cocoa production nationwide, eradicate fungicide misuse, increase cocoa production, reduce the risk of chemical poisoning by discouraging indiscriminate use of fungicide which will further ensure the availability of disease-free and non-toxic raw materials for cocoa processing industries; increasing farmers’ profit, foreign exchange values and internally generated revenue (IGR) from the sales of cocoa beans. The forecast system “ETAPOD” is user friendly, easy to interpret, highly proficient, reliable, and cost efficient, designed for monthly and annual BPD predictions. The installation and implementation of ETAPOD will help promote a disease free, clean and healthy environment.
Research locations
Twelve (12) research locations were mapped out from four important cocoa producing states in Southwest, Nigeria. The research locations are shown in Table 1 and their geographical positions shown in Figure 1.
Epidemiological data
The disease status (BPD incidence and severity) from the earmarked research locations were obtained from Etaware and Adedeji (2018).
Weather data
Weather data used for BPD prediction was collected from the National Bureau of Statistics (NBS) Ibadan and Nigerian Meteorological Station (Nimet).
BPD Prediction
The forecast system used for BPD prediction (ETAPOD) was developed by Etaware et al. (2018).
Data analysis
The geospatial data collected using Garmin eTrex® 10 GPS tracker were analysed and positioned on the map using the quantum geographic information system (QGIS 2.18.3) incorporated with GRASS 7.2.0 functions for optimization. The analysis of variance was carried out using COSTAT 6.451 software and homogeneity of means determined using Duncan Multiple Range Test (DMRT).
ETAPOD simulated BPD outbreak (ESBO) versus real life BPD outbreak (RLBO)
ETAPOD simulated BPD outbreak was 9.05% in Ondo (RLBO: 9.5%), 9.43% in Osun (RLBO: 9.0%), 11.5% in Ogun (RLBO: 0.0%), and 9.43% in Oyo (RLBO: 0.0%) in June 2015. In July, ESBO was 11.5% in Ondo (RLBO: 18.0%), 11.8% in Osun (RLBO: 13.5%), 12.2% in Ogun (RLBO: 0.0%), and 11.8% in Oyo (RLBO: 6.0%). In August, ESBO was 10.3% in Ondo (RLBO: 26.5%), 10.3% in Osun (RLBO: 8.0%), 11.2% in Ogun (RLBO: 3.0%), and 10.4% in Oyo (RLBO: 16.0%). In September, ESBO was 10.1% in Ondo (RLO: 11.0%), 10.3% in Osun (RLBO: 11.5%), 9.86% in Ogun (RLBO: 15.0%), and
9.98% in Oyo (RLBO: 14.0%). In October, ESBO was 8.17% in Ondo (RLBO: 5.0%), 7.8% in Osun (RLBO: 10.0%), 9.23% in Ogun (RLBO: 22.0%), and 7.80% in Oyo (RLBO: 0.0%), respectively (Figures 2, 3, 4 and 5 and Table 2). The comparison was based on the optimum cocoa production period (July-August) to October where most of the pods are harvested from the field.
The difference between ESBO and RLBO values in Ogun, Ondo, Osun and Oyo
It was also shown that the difference between real life BPD occurrences and predicted values was-8.58%≤ Ondo≤16.2%, -7.14%≤Osun≤2.20%, -11.5%≤ Ogun ≤12.8% and -9.43%≤Oyo≤5.60%, respectively (Table 3).
The level of accuracy of ETAPOD
ETAPOD accurately predicted BPD outbreak for Ondo and Osun for the period of June 2015 to March 2016 (Table 4). Although, the simulated BPD outbreak values from the forecast system was not 100% accurate for Ogun and Oyo, BPD predictions for August 2015 to March 2016 (Table 4) was within the range of real life occurrences for 2015/2016 cocoa production season in Nigeria.
The error of prediction for the developed BPD forecast model
The error in the predicted result from ETAPOD was estimated as follows: 0.20 (Ondo), 0.18 (Osun), 132.3 (Ogun), and 88 .92 (Oyo) in June 2015. 42.25 (Ondo), 2.89 (Osun), 148.8 (Ogun), and 33.64 (Oyo) in July; 262.4 (Ondo), 5.29 (Osun), 67.24 (Ogun), and 31.36 (Oyo) in August; 0.81 (Ondo), 1.44 (Osun), 26.42 (Ogun), and 16.16 (Oyo) in September; and 10.05 (Ondo), 4.84 (Osun), 163.8 (Ogun), and 60.84 (Oyo) in October 2015, respectively (Table 5).
ETAPOD was able to forecast BPD outbreak for the2015/2016 cocoa production season in Ogun, Ondo, Osun and Oyo states. ETAPOD accurately quantified BPD outbreaks in Ondo and Osun during the optimum season of cocoa production in Nigeria, but it failed to accurately predict the disease level for Ogun and Oyo.
This was in agreement with the research of Luo (2008) who stated that no forecast system can be 100% accurate at all times and that the accuracy level of any forecast system depends on several factors such as the credibility of the weather data fed into the system, the user proficiency of the forecast system, program errors, etc., which can be improved with time. The study was solely concerned with the maximum (March – October) and optimum (July – August) season of cocoa production and as such BPD information generated from ETAPOD was solely validated for those periods. It is known in Ghana that primary infection of cocoa pods in the field usually occur around June, but the peak of BPD infection generally occurred between August and October (Opoku et al., 2000, 2007). Information on the period for possible BPD infection in the field is useful in determining the pattern of disease development. Such information could be an important tool for disease management. The environmental conditions immediately preceding the infection period must be favourable for BPD development to occur and this period can be targeted for disease management.
ETAPOD is a warning system developed to ameliorate the devastating effects of black pod disease pestilence in Nigeria, within Africa and around the world, by providing useful information on the occurrence and spread of the disease with a clear coverage on the areas under severe attack. ETAPOD is unique as it is not geographically bound and thus, can be manipulated to provide optimum results wherever it is needed. A qualitative and quantitative description of the disease pressure was the key factor to determining the prevalence and spread of black pod disease in this study.
The authors have not declared any conflict of interests.
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