Spatial and temporal variability of plant-parasitic nematodes population in sugarcane

Nematodes are important pests of sugarcane crop in Brazil. However, no studies have been reported on the spatial and temporal variability of nematodes population in sugarcane fields and such studies are indispensable for the development of sampling plans, aimed at their application in integrated management programs. This work was carried out in two commercial fields of approximately 1 ha, both of them infested by Meloidogyne javanica and Pratylenchus zeae. In each area, samples represented by about 50 g of roots, were collected every two months, within a grid measuring 10.5 × 10 m (experiment 1) and 9.8 × 10 m (experiment 2). The highest nematodes populations were obtained during the rainy season, when high temperatures and moistures were favorable to root development. For this reason the rainy season was considered the best time to collect samples to identify areas with nematodes problem. Among the 52 calculated semivariograms (28 for M. javanica or P. zeae populations in area 1 and 24 for M. javanica or P. zeae populations in area 2), 22 could not be fitted to any model and presented a pure nugget effect. The spherical model showed the best fit to the semivariograms of data observed in the other 30 conditions. In those cases, values of range in semivariogram varied from 22 to 77 m, with 47 m on average and suggesting that, to obtain a reliable estimate for the population of these plant parasites in a given area, samples should be collected 47 m apart, which is equivalent to 1.5 sampling points per hectare. Nematóides são importantes parasitos da cana-de-açúcar no Brasil. Apesar disso, não há estudos sobre a variabilidade espacial e temporal de suas populações em canaviais e tais estudos são indispensáveis para o desenvolvimento de planos de amostragem, visando à aplicação em programas de manejo integrado. Por essa razão, realizou-se este trabalho, em duas áreas comerciais, de cerca de 1 ha cada uma, ambas infestadas por Meloidogyne javanica e Pratylenchus zeae. Em cada área, amostras representadas por cerca de 50 g de raízes foram coletadas aproximadamente a cada dois meses, em grid de 10,5 × 10 m (Ensaio 1) e 9,8 × 10 m (Ensaio 2). As populações de nematóides mais elevadas foram obtidas na estação chuvosa, quando as altas temperaturas e umidade favorecem o desenvolvimento das raízes das plantas. Assim, esta estação foi considerada a melhor para coleta de amostras visando identificar áreas com problemas nematológicos. Entre os 52 semivariogramas calculad