THE EFFECT OF TEMPERATURE ON THE DEVELOPMENT OF EPIDEMICS OF COFFEE LEAF RUST IN PAPUA-NEW-GUINEA

Epidemics of coffee leaf rust (CLR) were monitored to establish the se asonal pattern of epidemic development in various coffee growing regio ns of Papua New Guinea (PNG) and to determine the effect of temperatur e on those epidemics. There is a seasonal pattern to the epidemics of CLR in PNG. Rust incidence (% infected leaves) is lowest during the Oc tober-November to January-February period. Thereafter rust incidence i ncreases and reaches a peak in May-June-July, after which the disease incidence declines. The average maximum disease incidence (MDI) was le ss than 20% leaves infected. MDI was positively correlated with the me an minimum monthly temperature five months before the MDT. This associ ation indicated that if the average minimum temperature is less than 1 5 degrees C in January, epidemic development 5 months later will not r each levels which require chemical control. The minimum temperatures r ecorded in PNG suggest that conditions are sub-optimal for the develop ment of epidemics of coffee leaf rust in the main coffee growing areas of the country. The possibility that CLR became established in the ma in coffee growing regions of Papua New Guinea before 1986 and remained undetected for a number of years is discussed.