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Coffee Leaf Rust

Coffee Leaf Rust caused by Hemelia vastatrix is the most well known coffee disease. It was first detected in 1861 in the lake Victoria Area of Kenya. In 1869 it was found in Sri Lanka (former Ceylon), where it spread over the whole coffee growing areas worldwide, except the growing areas of Hawaii.

Symptoms

Yellow to orange powdery spots appear on the underside of leaves, with corresponding chlorotic patches on the upper side. Initially these are only 2-3 mm in diameter, but steadily expand and can eventually reach a diameter of several centimeter. Young lesions may appear as small chlorotic spots before sporulation occurs. The centers of older lesions become necrotic and the sporulating zone is restricted to the outermost zone.

A major effect of the rust is to cause defoliation. Symptoms are visible 2 t0 3 weeks after infection. Sporulation occurs after 2 to 8 weeks.

Coffee Leaf Rust Infection

Uredospores need free water to germinate and to form an appressoria. Germination takes place within 2 to 10 hours depending on climate conditions. Appressoria formation takes less than 6 hours under optimum condition. At least after 22 to 24 hours the infection process is finished.

Requirements for Infection

  • Leaf Wetness
  • Darkness
  • Air Temperature in between 15°C and 28°C
  • Optimum Air Temperature is 22°C to 25°C


The Coffee Leaf Rust Infection Model shows the progress of weak, moderate and severe Infections. The graph below shows an infection for the 7th and 8th of March for Sabukia Kenya. A weak infection could be completed and a moderate infection could be nearly completed, where the leaf wetness was not lasting long enough to complete an severe Infection.

Coffee Leaf Rust Infection Severity:

  • The severity of an infection is depending on the:
  • Quantity of Spores
  • Distribution of Spores
  • Portion of Spores germinating and infecting during the given leaf wetness period.


The quantity of spores can not be accessed on base of weather data. For the spore distribution we have the factor wind and rain. In a dry atmosphere spores will be distributed by wind. During a rain storm splashing rain will distribute the newly formed spores which might be the most virulent ones.

Coffee Leaf Rust Infection Severity Model

  • The severity of an infection is calculated by the:
  • Sum of rain during during infection
  • If it was a weak, moderate or severe Infection


The FieldClimate.Com Coffee Leaf Rust Severity Model uses the following decision system:

  • if CLRsevere=100% and rainsum >= 5 then CLRseverity := 5 else
  • if CLRmoderate=100% and rainsum >= 10 then CLRseverity := 5 else
  • if CLRsevere=100%  and rainsum > 2 then CLRseverity := 4 else
  • if CLRmoderate=100% and rainsum >= 5 then CLRseverity := 4 else
  • if CLRsevere=100% then CLRseverity := 3 else
  • if CLRmoderate=100% and rainsum >= 2 then CLRseverity := 3 else
  • if CLRweek=100% and rainsum >= 10 then CLRseverity := 3 else
  • if CLRmoderate=100% then CLRseverity := 2 else
  • if CLRweek=100% and rainsum >= 2 then CLRseverity := 2 else
  • if CLRweek=100% then CLRseverity := 1 else CLRseverity:=0

Coffee Leaf Rust Infection Severity Model

The severity for the coffee leaf rust infection at the 7th and 8th of March at Sabukia, Kenya was rated to be 2. There was only a weak infection and it was raining more than 2 mm.
Looking for the daily values might give a better overview about the situation. This graph shows the sevirity value of Coffee Leaf Rust and Coffee berry disease together with the Propagation potential of Bacterial Blight. This data are again form Sabukia, Kenya. We can see some Coffee Leaf rust Infections in the second week of February and beginning with the forth week of February a higher incidence of Coffee Leaf Rust Infections with higher severity ratings.