Mycena citricolor (American leaf spot of coffee)

On coffee, subcircular spots initially brown becoming pale-brown to straw-coloured are produced mainly on leaves. The spots have a distinct margin and are 6-13 mm diameter but with no halo. The mycelium tends to be luminous giving the spots a bright appearance in the shade. Mature spots become lighter and develop minute, yellow, hair-like gemmifers 1-4 mm long consisting of a thin pedicel surmounted by a spherical gemma about 0.4 mm diameter. Gemmifers are mostly produced on the upper surface of spots. The centres of older leaf spots may disintegrate giving a 'shot hole' appearance. Similar spots may be produced on stalks and berries. The main effect is to cause leaf fall with a consequent reduction in growth and yield of the coffee tree. Symptoms on other hosts are broadly similar (Wellman, 1972).

Cultural control measures aimed at reducing inoculum sources such as badly diseased trees and infected shade trees have had some success (Wellman, 1950). As the disease spreads slowly sanitation methods should have a significant impact but may be difficult to execute effectively in smallholder coffee. Application of fungicides continues to be used in areas where the disease is problematic. Bordeaux mixture and other copper fungicides are effective (Echandi and Segall, 1958). Triazole systemic fungicides are now most effective (Vargas et al., 1990) and application of calcium hydroxide has been shown to suppress symptoms due to the neutralization of oxalic acid produced by the pathogen (Rao and Tewari, 1988). There have been several investigations of the use of biological control agents; Vargas (1984) reduced the disease by applying coffee grindings inoculated with Trichoderma harzianum, antagonistic bacteria isolated from diseased coffee were used by Calvo and Vargas (1989) and Mora et al. (1989), and a Bacillus species was used by Quesada and Jimenez (1996).
 

M. citricolor can cause significant defoliation in some localities. The result of this is reduced growth of coffee trees producing less bearing wood to carry the following season crop. Severe defoliation may also cause berry shedding and reduced quality of the current season's crop. In humid shaded coffee in some Central American countries losses of up to 20 or 30% have been estimated (Wellman, 1972) but Bonillo (1982) estimated losses of up to 73% in El Salvador.