Prolonged wet weather combined with below average temperatures fostered the growth of coffee rust fungus that could reduce 2005/06 (July/June) tree yields by about 50 percent, agronomists said.
They said that the hemileia vastatrix strain of the disease, which causes coffee trees to shed their leaves, is causing concern among coffee farmers in key regions such as the southern part of Minas Gerais state.
"Coffee rust is a long standing problem but it is developing resistance to fungicides," said Jose Luis Rufino, coffee manager at the government's agricultural research agency Embrapa.
Coffee trees have also become weaker and more vulnerable to the disease as farmers cut back on fertiliser and crop care products due to depressed prices over the past four years.
Farmers also can't afford to pay for anti-rust fungicides whose prices have risen sharply due to a supply shortage following strong demand from Brazil's soybean farmers seeking to curb an more aggressive Asian soy rust disease.
Similar fungicides are used to control soy rust which caused an estimated 3.4 million tonnes in production losses in 2002/03 (October/September) and is expected to cut output even further this year.
"The (coffee rust) problem has grown much worse due to excessive rains and difficulty finding and paying for fungicides," said Leonard Biscaro Japiassu, agronomist at the agriculture ministry's Procafe technical support agency in Varginha, Minas Gerais.
Rainfall in February at the research station totalled 303 millimeters (11.9 inches), compared with an average 178.8 mm (7 inches) February average between 1974/2003.
Temperatures averaged 21 Celsius (70 Fahrenheit) in February, compared with 23 C (73 F) for the same month between 1974/2003.
The rate of rust infection rose to an average 24.5 percent in February, from 20 percent in January. Infection reached 60 percent in densely planted trees heavily laden with coffee fruit.
"Cool, humid conditions favoured an increase in the disease which farmers must carefully monitor and spray fungicides if necessary," he said.