Dieback of cocoa (Theobroma cacao L.) plant tissues caused by the brown cocoa mirid Sahlbergella singularis Haglund (Hemiptera: Miridae) and associated pathogenic fungi

Abstract

The brown cocoa mirid,Sahlbergella singularisis the most important insect pest of cocoa for field damage has been classified into three categories that include blast, stagheadedness and mirid pocket. The mirid attack predisposes the cocoa plant to secondary infection by opportunistic pathogenic fungi. This study evaluated the dieback conditions associated with mirid damage due to associated fungi from lesions on pods, twigs and pin punctures. The relationship betweenPhytophthorablack pod infection and mirid infestation in the field was also established. The results indicated that dieback progression from the mirid lesions (8.5 mm) was significantly different (P< 0.05) from that of pin punctures (7.8 mm).Lasiodiplodia theobromaehad the highest proportion of isolates from pods (33%), twigs (47%), and pin punctures (38%).Fusarium decemcellulare(Albonectria rigidiuscula) accounted for 27.8% and 31.6% from pods and twigs; however, it was not recovered from pin punctures. Other isolated pathogens wereAspergillusspecies andRhizoctoniaspecies. There was a significantly strong positive correlation coefficient of 0.74 between the mirid population and the black pod disease infection in the field. The major fruit-bearing season of cocoa witnessed an increase in mirid infestation and blackpod infection. The effect of mirid–pathogenic fungi-associated damage could be ameliorated through effective crop husbandry practices to ensure that cocoa plant tissues are not unduly exposed to biological and mechanical injuries.