The effect of temperature on the development of epidemics of coffee leaf rust in Papua New Guinea

Abstract

Epidemics of coffee leaf rast (CLR) were monitored to establish the seasonal pattern of epidemic development in various coffee growing regions of Papua New Guinea (PNG) and to determine the effect of temperature on those epidemics. There is a seasonal pattern to the epidemics of CLR in PNG. Rust incidence (% infected leaves) is lowest during the October-November to January-February period. Thereafter rust incidence increases and reaches a peak in May-June-July, after which the disease incidence declines. The average maximum disease incidence (MDI) was less than 20% leaves infected. MDI was positively correlated with the mean minimum monthly temperature five months before the MDI. This association indicated that if the average minimum temperature is less than 15 °C in January, epidemic development 5 months later will not reach levels which require chemical control. The minimum temperatures recorded in PNG suggest that conditions are sub-optimal for the development of epidemics of coffee leaf rust in the main coffee growing areas of the country. The possibility that CLR became established in the main coffee growing regions of Papua New Guinea before 1986 and remained undetected for a number of years is discussed.