Sampling procedures and damage thresholds for root-knot nematode (Meloidogyne javanica) on pineapple

The relationship between the population density of root-knot nematode (Melo idogyne javanica) and pineapple yield was studied by establishing different nematode densities in field plots at 3 sites. Differences in nematode popu lations between treatments were apparent 9-22 months after planting, but yi elds in the plant crop were similar, regardless of nematode density. In the ratoon crop, yields in treatments with less than 10 nematodes/200 mt soil at 9-22 months were reduced by about 10%. Yield reductions of more than 25% occurred when population densities were greater than 50 nematodes/200 mt. soil. These results demonstrate that economically significant crop losses f rom root-knot nematodes can occur in pineapple when the population density at 12 months is greater than 1-5 nematodes/200 mt soil. The sampling procedures required to obtain reliable estimates of M. javanic a in pineapple fields were determined by studying nematode distribution in 2 fields in south-east Queensland. Nematodes were extracted from more than 100 individual soil cores on a 5 by 5 m grid and populations were found to have a clumped rather than random distribution. A composite sample of 41 co res in 1 field and 72 cores in the other gave a relatively precise estimate of the population of root-knot nematodes (i.e. standard error: mean ratio of 0.3). These data suggest that a 50-core sampling unit is appropriate whe n nematode population density is being estimated for decision-making purpos es.