Farmers have been upbeat this season about the healthy mix of rain and sun in primary growing regions that could boost output early in the season, which started on Oct. 1.

However, heavy rainfall during the early weeks of the October-to-March main crop has spread disease, including brown rot and black pod disease, threatening the crop later.

Six exporters interviewed by Reuters said they expected arrivals at the ports of Abidjan and San Pedro to drop to between 300,000 and 350,000 tonnes in the first quarter of next year, down from 570,000 tonnes over the same period this year.

"Right now production is more or less normal and consistent with our expectations, even if slightly lower than last season," the director of an Abidjan-based international export company said on Wednesday.

"But production is going to slow down even more, starting in January, and we were not really expecting that."

Ivory Coast, the output of which accounts for about 40 percent of global cocoa supply, produced a record harvest of more than 2 million tonnes of beans during the 2016/17 season, but farmers' earnings were hit by falling world prices.

Many could not afford to apply fertilisers and pesticides in the months leading up to the start of the main crop this year, making their pods increasingly vulnerable to disease.

"At the beginning of the season, we saw that production was very good across the board. But after the rains and because of the lack of treatment, we're seeing that production is no longer good," said Sylla Keita, a farmer in the southwestern region of Soubre.

"There are too many rotten pods and also too few cherelles."

Production in Ivory Coast could also be depressed by ethnic conflicts that in recent weeks have forced thousands of people to flee forest reserves that contain illegal plantations.