Ghana cut its forecast for the current season’s cocoa harvest by 6 percent because of plant disease in its biggest growing region, according to two people familiar with the matter.

The regulator of the world’s second-biggest cocoa producer lowered the production estimate for the annual crop through September to 850,000 metric tons, from 900,000 tons previously, said the people, who asked not to be identified because the information isn’t public.

Cocoa plantations have been infected with the swollen shoot virus, which can cause abnormally shaped pods and lead to lower yields, said the people. While the sickness is not uncommon across cocoa growing regions in West Africa, the current outbreak in western Ghana is particularly severe, they said.

Hot, dry weather in the first quarter and aging trees are also contributing to a smaller crop, said a third person.

A spokeswoman for Ghana Cocoa Board declined to comment when visited at her office.

Cocoa production in Ghana is set to slow after the harvest got off to a quick start this season, with bean purchases exceeding the previous year’s by a fifth in the first two months through November. The difference narrowed to 5.4 percent by March 28, when the regulator’s purchases totaled 693,685 tons.

The country accounts for close to a fifth of global output and produced 899,209 tons last season.