Germination and penetration studies on coffee rust (Hemileia vastatrix B. & Br.)

SUMMARY Spore dispersal, germination, penetration and incubation‐period studies on coffee rust ( Hemileia vastatrix B. appressoria may continue to form. In the field, appressorium formation and infection can occur between 10 p.m. and 8 a.m. If coffee trees are wet at dusk or rain falls before midnight, infection is probable and it is proposed that the number of occasions this occurs be used to forecast the severity of the annual rust maximum. The median incubation period throughout the year varied from 4 to 7 weeks, increasing with low temperatures and dry conditions. A multiple regression of mean maximum and minimum temperatures on incubation period gave fair agreement between observed and computed values for Ceylon and Mysore. Susceptibility and incubation period were strongly affected by coffee variety and rust biotype, but not by age of leaf or crop size.