Economic evaluation of the incidence of yellow leaf spot disease on the yield of ginger in the rainforest agro ecology of Nigeria
This study evaluated the economic effects of the incidence of yellow leaf spot disease on cost of production and yield of ginger. A field experiment was conducted at the research farm of National Root Crops Research Institute Umudike in Abia State in 2014 and 2016 planting seasons. The study involved six treatments replicated two times. Three (3) rates of Ridomyl and Z-force (both fungicides) each were applied in a completely randomized block design, during the two year cropping season. Data were collected on weekly, bi-weekly and monthly bases depending on treatment, the incidence of leaf spot disease was assessed by counting the number of infected plants per plot which also depends on the number of sprouted plants and this was done between 13WAP and 24WAP when infestation was most prevalent. The economic evaluation of the incidence of yellow leaf spot on the yield of ginger was done using a modified gross income analysis by holding other variable costs constant for all the treatments except the cost of controlling yellow leaf spot, which is assumed to be the only source of variability among the treatment combinations. The result showed that all the plots, including the control had varying levels of incidence of leaf spot disease, implying that none of the treatment combinations were able to completely eradicate yellow leaf spot in the study area. However, it was observed that incidence becomes critical if it is above 20%. This implies that although yellow leaf spot is likely to infect ginger crops in the rainforest zone, its yield may not be critically affected below 20% infestation. TR3 (R. 7g/monthly) had the highest gross income of ₦2,488,500 with TR1 recording the highest cost implication of ₦125,000. Also, TR12 (Z. 7.5g/monthly) had the least cost implication of ₦16,000. Results showed no significant difference in yield and value of output among the treatment means in 2014 and 2016. Further analysis indicated that a significant difference existed in the incidence of yellow leaf spot in 2014 and 2016, with 2014 recording higher incidence. It was therefore concluded that yellow leaf spot is most likely to occur in ginger farms located in the tropical rainforests of Nigeria. But only disease incidences above 20% are likely to affect the economic yield of ginger in the study area. It is therefore recommended that Redomyl 7g applied monthly to check incidence while optimizing the best economic return.
Keywords: Ginger, yellow leaf spot, incidence, yield, control, and fungicides