Estimation of Meloidogyne javanica damage thresholds in sweetpotato

Damage threshold of root-knot nematodes (RKN) is the nematode density at which the yield begins to decrease significantly [1]. It is the foremost important factor to consider prior to crop establishment to avoid unexpected crop losses or unnecessary chemical/ control measure applications. Various models have been used to estimate the damage functions of plant-parasitic nematodes in different crops. In annual crops such as vegetables, the severity of damage caused by RKN is related to the number of nematodes present at planting [2]. It may be as low as 1 nematode/200 g soil for particularly susceptible crops such as carrots, or where conditions are conducive with hot climates and sandy soils [2]. However there is no evidence for specific RKN damage threshold identified for sweetpotato, although it is an important crop to Australia worth of $80 million annually [3]. Yield losses from RKN infestation in untreated local sweetpotato fields could be as high as 57% based on recent surveys in different Queensland regions [4]. The objective of this experiment was to estimate the damage threshold of RKN in sweetpotato in red ferrosol and grey sandy soils.