Plant-parasitic Nematodes in the Waimanalo, Hawaii Irrigation System from Watershed to Farm

Abstract

Nematode occurrence at specific locations throughout a water catchment-irrigation system was determined. Soil samples were collected from five water source locations on the slopes of Olomana Mountain and Maunawili Valley and from about 40 plant species on 18 farms (56 ha of 480 ha irrigated by the reservoir). Water was sampled from the catchment reservoir at 0.3 m, 9 m, and 18 m (bottom). A farm irrigated with potable water was sampled and compared to areas of the same farm irrigated from the reservoir. Nematodes present in soil from the mountain and farms were root-knot (Meloidogyne spp.), lesion (Pratylenchus spp.), reniform (Rotylenchulus reniformis), stunt (Tylenchorhynchus sp.), ring (Criconema spp.), dagger (Xiphinema sp.), spiral (Helicotylenchus sp.), Tylenchus sp., Aphelenchus sp., and pin (Paratylenchus sp.) nematodes. The economically important genera Rotylenchulus, Meloidogyne, and Pratylenchus occurred in very low numbers (10, 41, and 10/250 cm³ soil, respectively) and in low frequency (10%, 25%, and 8% of the samples, respectively) in the mountain samples compared with high numbers (170-895/250 cm³ soil) from farms. Frequency of occurrence over all farms was near 40% for Meloidogyne and 80% for Rotylenchulus. No nematodes were detected in water from the reservoir. One sample from the outlets contained two specimens of plant-parasitic nematodes. The population densities of nematodes were not different between the soil samples collected from crops irrigated by potable or reservoir water.