A PRELIMINARY STUDY ON IMMATURE NUTFALL OF COCONUT WITH REFERENCE TO PEST DAMAGE
Authors: Rajapakse C. N. K. , WIJESEKAEA H. T. R. , NORMAN A. H. 
Published: March 2013

Buttons and immature nut shedding before and after fertilization is a commonproblem in coconut. In general, about one third of the buttons produced in aninflorescence develop into mature nuts. The number of buttons produced in a bunchoften exceeds the number of nuts reaching maturity. Immature nutfall in coconut hasbeen attributed to various factors such as natural capacity for production, physiologicaland environmental factors, and pest damages.It was reported that a coconut inflorescence commencing with an average of 16female flowers or potential nuts loses 2 4% during the first two months, 40% during thesecond two months and 2% during the third two months of their development(Abeywardene and Mathes, 1971). Fungal infection has been identified as one of themain causes of immature nutfall in coconut (Quillec et al, 1984). Several species ofinsects have also been recorded as pests of immature nuts, which cause developing nutsto shed (Fernando and Kanagaratnam, 1989). However, no attempts have been made toquantify the effect of insect pests and pathogens on immature nutfall in coconut. Thepresent study was undertaken to categorize and quantify the pest damages which areresponsible for immature nutfall in coconut.Total of twenty healthy palms were selected and a nylon net basket was hung justbelow the selected inflorescence in each palm soon after the opening of theinflorescence. Fallen nuts were collected daily during the first two months and at weeklyintervals thereafter over a six month period, and were then categorized according to thecause of nutfall.Three major factors, namely microbial infections, insect pest damages andphysiological reasons were identified as predominant causes for nut shedding. Microbes,especially fungal infections were identified by the light brown to dark brown patcheswith water soaked appearance and the presence of mycelium in the perianth region andin the inner tissues. Isolations were performed on discoloured tissues. Insect attackswere identified by their presence, feeding signs, larval tunnels, webbing and scrappingmarks on the immature nuts. Immature nuts fallen due to physiological disorders wereidentified by their healthy appearance and characteristic uniform browning of the nuts.ation is a commonproblem in coconut. In general, about one third of the buttons produced in aninflorescence develop into mature nuts. The number of buttons produced in a bunchoften exceeds the number of nuts reaching maturity. Immature nutfall in coconut hasbeen attributed to various factors such as natural capacity for production, physiologicaland environmental factors, and pest damages.It was reported that a coconut inflorescence commencing with an average of 16female flowers or potential nuts loses 2 4% during the first two months, 40% during thesecond two months and 2% during the third two months of their development(Abeywardene and Mathes, 1971). Fungal infection has been identified as one of themain causes of immature nutfall in coconut (Quillec et al, 1984). Several species ofinsects have also been recorded as pests of immature nuts, which cause developing nutsto shed (Fernando and Kanagaratnam, 1989). However, no attempts have been made toquantify the effect of insect pests and pathogens on immature nutfall in coconut. Thepresent study was undertaken to categorize and quantify the pest damages which areresponsible for immature nutfall in coconut.Total of twenty healthy palms were selected and a nylon net basket was hung justbelow the selected inflorescence in each palm soon after the opening of theinflorescence. Fallen nuts were collected daily during the first two months and at weeklyintervals thereafter over a six month period, and were then categorized according to thecause of nutfall.Three major factors, namely microbial infections, insect pest damages andphysiological reasons were identified as predominant causes for nut shedding. Microbes,especially fungal infections were identified by the light brown to dark brown patcheswith water soaked appearance and the presence of mycelium in the perianth region andin the inner tissues. Isolations were performed on discoloured tissues. Insect attackswere identified by their presence, feeding signs, larval tunnels, webbing and scrappingmarks on the immature nuts. Immature nuts fallen due to physiological disorders wereidentified by their healthy appearance and characteristic uniform browning of the nuts.Results revealed that 5 % of nuts dropped due to insect pest attacks. Insect damagewas high (3%) in the first two months after fruit setting. Insects responsible wereidentified as mealy bugs (Dysmicocus sp), Scale insects (Aspidiotus destructor). Mites(Dolichotetranychus sp), larvae of the moth, Cyclodes omma and a weevil (Meridolussp). Insect pest damages were negligible during the second two months after fruitsetting. However, immature nutfall increased, in the last two months (fifth and sixthmonths after fruit setting) due to the increase rat and bat damages to tender nuts.Fungal infections were comparatively high during the first four months resulting in a17% immature nutfall. In first and second two month periods 7% and 9% of nuts wereobserved fallen due to fungal infections. Thereafter nut shedding due to fungalinfections was negligible. Fusarium sp was identified mainly in fallen nuts. As thefungal infections are responsible for considerable loss of immature nuts, thoroughinvestigations are needed to evaluate the role of fungi. Results also indicated that a totalof 38 % of immature nuts fall is due to physiological reasons. This was observed mainlyduring the first two months of fruit setting. The main reason could be the natural limitedcapacity of the palm.The losses due to pest damages could be minimized by using appropriate controlmeasures. This study suggests that a minimum of 20 % yield increase can be assuredby controlling the pest and microbial attacks on immature nuts.