Seasonal fluctuations in plant-parasitic nematode vertical distributions and their interactions with edaphic factors in vegetable fields of South Georgia, USA

Plant-parasitic nematodes (PPNs) can be found deep in the soil profile, compounding nematode management decisions and detection. This study aimed to understand how seasonal fluctuations in edaphic factors are associated with the vertical distribution of PPNs in south Georgia’s vegetable cropping systems. Five-core composite soil samples were taken monthly (March 2020 to February 2022) at three random locations in six vegetable fields. Fields represented 4 cropping systems (vegetable plasticulture, bare-ground cucumber, and plastic-bed watermelon rotation) and two regions (north and south) sampled from five 15-cm strata (0-15 cm, 15-30 cm, 30-45 cm, 45-60 cm, and 60-75 cm). Only soil temperatures and precipitation had seasonal fluctuations, while the other edaphic factors were vertically stratified. Latitude and stratum had the strongest associations with the nematode composition, showing a clear separation between the north and south regions. Variations in soil texture, porosity, moisture, and PPN vertical distribution suggest that the illuvial zone in the north region was the main factor in differences observed between regions and strata. Seasonal fluctuations in vertical distribution were found among Meloidogyne incognita and Nanidorus spp. Higher abundances of deep-dwelling PPNs were limited to the south region in the winter for M. incognita and summer and winter for Nanidorus spp., probably due to the illuvial zone barrier in the north region. Since most root-knot nematodes dwell at ≤ 30 cm during the summer, fumigants/nematicide applications are recommended during this season to minimize the risk of deep-dwelling escapees.