A wheat field shows symptoms of leaf rust. The disease triangle requires (i) a susceptible host, (ii) a virulent pathogen, and (iii) a favourable environment. The average nightly temperature is 18 °C, relative humidity is 85 % for 8 h, and leaf‑wetness lasts 6 h per day. The pathogen needs a minimum temperature of 15 °C, relative humidity  80 % for at least 5 h, and leaf‑wetness  4 h to infect. (a) Are the present conditions conducive for infection? (b) If the probability that each individual condition occurs on a given day is 30 % for temperature, 25 % for humidity, and 20 % for leaf‑wetness, assuming independence, calculate the overall daily infection risk as a percentage. (c) Recommend one cultural control measure that targets the most influential condition.

Question

A wheat field shows symptoms of leaf rust. The disease triangle requires (i) a susceptible host, (ii) a virulent pathogen, and (iii) a favourable environment. The average nightly temperature is 18 °C, relative humidity is 85 % for 8 h, and leaf‑wetness lasts 6 h per day. The pathogen needs a minimum temperature of 15 °C, relative humidity > 80 % for at least 5 h, and leaf‑wetness > 4 h to infect. (a) Are the present conditions conducive for infection? (b) If the probability that each individual condition occurs on a given day is 30 % for temperature, 25 % for humidity, and 20 % for leaf‑wetness, assuming independence, calculate the overall daily infection risk as a percentage. (c) Recommend one cultural control measure that targets the most influential condition.

Accepted Answer

a) Yes, conditions are conducive. b) 1.5 % daily infection risk. c) Adjust sowing date to avoid the favourable temperature period (targets the temperature condition).

Gce Model Questions Vol1 2017 Agricultural Science Question 4

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