Neco 2018 Agricultural Science Question 3

In a field of 200 plants, 30 show symptoms of a leaf‑spot disease. Of the symptomatic plants, 80% have lesions covering less than 10% of leaf area, while 20% have lesions covering more than 30% of leaf area. The disease is caused by a fungus that requires a minimum leaf‑wetness period of 6 hours for infection. Weather records indicate an average leaf‑wetness duration of 5 hours, but irrigation adds 2 hours of wetness to 40% of the field. Determine (a) the disease incidence in the field, (b) the proportion of the field that is at risk of infection because the leaf‑wetness requirement is met, and (c) give an integrated management recommendation that includes cultural, chemical and resistant‑variety measures.