Sugarcane yield loss in the ratoon crop carried over from the plant crop damaged by plant-parasitic nematode in a heavy clay field in Okinawa, Japan

Many field experiments have revealed sugarcane yield loss due to plant-parasitic nematodes, especially in sandy soil, but limited in clay soil. We previously reported a 15% sugarcane yield reduction in the plant crop in a heavy clay soil due to lesion nematodes suppressing the number of sugarcane tillers in the early growth stage (Kawanobe et al., 2016). Yet, it is unknown whether such early growth inhibition in plant canes will affect the ratoon crop yield in clay soil. The objective of this study was to examine the carry-over effect of yield decline from the plant crop to the ratoon crop in a field with high clay content (> 80%), in which early growth inhibition, possibly due to lesion nematodes, was observed in a plant crop of sugarcane. Though the Pratylenchus population density remained unchanged among treatments (fosthiazate-treated, 3 kg and 7.5 kg/ha at spring planting, and non-treated control), after 5 months (July) from the spring planting until the harvest of the ratoon crop, our study showed a 20–25% higher yield of the ratoon crop in the fosthiazate-treated crop than in the non-treated control. The result in the plant crop carried over to the ratoon crop, and implied that the healthier root growth of the plant canes achieved by a one-time nematicide application would carry-over to the ratoon crop. The result also suggested that the number of tillers and cane length observed at 5 months (July) in the ratoon crop might adequately reflect nematode damage and offer a good explanation for the level of the ratoon crop yield.