Guatemalan coffee growers look like running the gauntlet of rust outbreaks for some years thanks to uncertainties over tree varieties resistant to the fungus, which has prompted officials to urge against replantings for now.
The Central American coffee rust outbreak caused even bigger losses to Guatemalan production than originally thought, US Department of Agriculture staff in Guatemala City said, cutting their forecast for the 2013-14 by 480,000 bags to 3.42m bags.
At that level, production would represent a 20-year low, down 19.8% on the previous season, which itself saw some damage from the initial phase of the outbreak of rust, which causes defoliation and heavy yield losses, and can lead to tree death.
The disease had become "an epidemic, dispersing geographically and with higher intensity, and greater impact on trees", the USDA staff said in a report.
However, while many countries have responded to coffee rust outbreaks by encouraging mass programmes of replanting with trees resistant to the fungus, Guatemalan growers are being urged to hold-off.
Anacafe, the Guatemalan coffee association, "is urging farmers to resist the temptation of quickly replanting" with existing rust-resistant trees "until it becomes clearer that those existing varieties produce good-tasting coffee, and are not susceptible to other coffee diseases", the briefing said.
"Rust resistant/tolerant varieties experience other diseases."
Farmers in some other countries have complained over the yields and cupping quality of beans from rust resistant trees, such as the Castillo type which has been sown in Colombia.
Some Colombian growers have preferred to stick with traditional varieties, and fork out for fungicides, while others have mixed plantings of Castillo and historic types, often planting rust resistant trees as a buffer around stands of other varieties.
In fact, Guatemalan growers have had some success in limiting rust damage, especially in plantations at higher altitudes, with the greater humidity and higher temperatures at areas below about 2,500 feet encouraging the spread of the disease.
"With proper, adequate tissues management, coffee is not nearly as devastating as what has been reported," the briefing said.
"Cultural management of the planting tissue, together with adequate nutrition, and preventive spraying during the vegetative and flowering phases, leads to a good coffee harvest."
The USDA bureau forecast Guatemala's coffee harvest recovering "slightly" in 2014-15 to 3.62m bags.
USDA staff have also forecast small recoveries in coffee output in El Salvador and Mexico, also struck by rust, but the fungus is expected to depress further Costa Rican production in 2014-15.