Integrated management of sting nematode in newly planted citrus trees

Integrated management of sting nematode in newly planted citrus trees

Report Date: 04/05/2022
Project: 21-013   Year: 2021
Category: Horticultural & Management
Author: Larry Duncan
Sponsor: Citrus Research and Development Foundation

 During October 2021-Janury 2022 we surveyed sting nematode populations in several Polk and Highlands County orchards before focusing on 12 quadrats (all moderately-highly infested) across 30 acres of a declining grove near Babson Park destined for replanting in spring 2022.  The nine-year-old trees in the grove were clipped to preserve the current irrigation system; however, the grower uprooted 20 trees throughout the grove, revealing uniformly severe root damage on all trees immediately below 30 cm depth.  There were relatively fewer symptoms on the surface layer of fibrous roots supporting the need for deep soil sampling to accurately assess sting nematode abundance in citrus.  The extensive and comprehensive damage to root systems by sting nematode suggested that the grove would be suitable for the trial.Three hundred trees (Valquarius on 812) were planted on 3/22/2022 and half the trees were covered immediately with individual protective covers (IPC).  The design of the experiment is a completely randomized block with 15 blocks, each with 4 factorial treatments (all combinations of IPCs and nematicide application), each applied to 4-tree plots. Plots are separated by single buffer trees. Thus, we will evaluate the effect of sting nematodes on trees exposed to or protected from Asian citrus psyllids that are treated or not treated for nematode control.  We dissassembled the fittings and poly-tubing used to deliver nematicides to 32, 4-tree plots in a previous experiment and reconfigured and installed the equipment in these 15 blocks. The first nematicide treatment will occur in April 2022 and will occur in each autumn and spring thereafter. In November 2020 we collected sting nematode-infested soil from a citrus orchard and extracted and handpicked 30-50 mixed-stage individuals per 8 pots each of St. Augustine grass and sorghum sudangrass to establish cultures to serve as inoculum for trials to evaluate tolerance of rootstocks to sting nematode.  Within two months, sampled pots contained as many as 40 nematodes per cm3 of soil.  In December 2022 we autoclaved Candler sandy soil and filled 4, 150 gallon tanks in a greenhouse. St. Augustine grass stolons and soil from the nematode cultures were transplanted into two of the tanks in January.  the other two tanks were planted with non-infested St. Augustine.  Construction on the greenhouse that began in early January was still ongoing in April, precluding further research until completed.    


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