Enhanced biodegradation of nematicides after repetitive applications and its effect on root and yield parameters in commercial banana plantations

The effects of five consecutive applications, every 4 months, of Counter, Furadan, Mocap, Nemacur, Rugby, and Vydate on functional root percentage, production parameters, and on enhanced biodegradation were compared in a commercial banana plantation in Costa Rica. To quantify nematode numbers and estimate functional root percentage, root samples were taken monthly from the field experiment. The enhanced biodegradation test was carried out in the laboratory. Samples taken from the field after five consecutive applications of each nematicide were treated in the following way: (1) not sterilized and no nematicide applied; (2) not sterilized but nematicide applied; and (3) nematicide applied after sterilization. The number of Radopholus similis which had penetrated the maize plantlets was used as a parameter to determine the degradation of the applied nematicide. Degradation was measured 0, 2, 4, 6 and 8 weeks after inoculation of pregerminated maize plantlets with 500 nematodes in soil under laboratory conditions. At harvest, 20 months after starting the field experiment, the lowest percentage of functional roots (P=0.024) and bunch weight (P=0.0001) were found in the non-treated control, followed by the Furadan treatment. On average, nematicides increased the bunch weight by 38%. In general, higher bunch weights coincided with higher percentages of functional roots. Furadan showed a high level of enhanced biodegradation while for Counter and Rugby this phenomenon was not detected. In the case of Mocap and Nemacur, a relatively high level of enhanced biodegradation in the soil biotest coincided with a high number of nematodes per 100 g roots in the field experiment. A high correlation between mean nematode numbers per 100 g roots and mean percentage of functional roots was observed (R2=0.81, P=0.006) for all treatments together. Data show that a rotation of different nematicidal molecules is the best option for long-term nematode management in commercial banana plantations.