Effects of low risk nematicides on nematode community, microbiome and nutrient cycling in cantaloupe rhizosphere in low desert of California
Agronomy & Pest Management
Philip Waisen
Dr.
UCCE Riverside
Palm Desert
Abstract
Root-knot nematode (RKN; Meloidogyne spp.) is a major concern on fruiting vegetables in desert valleys of southern California and exacerbated by state’s stringent regulations on pesticide use. A field trial was conducted in the spring of 2025 in Coachella Valley to examine the effects of low risk nematicides on nematode, bacterial and fungal communities, and nutrient cycling on cantaloupe. The treatments included Vydate (oxamyl; 9.4 L/ha), Velum (fluopyram; 0.5 L/ha), Salibro (fluazaindolzine; 2.3 L/ha), Majestene (Burkholderia sp; 9.4 L/ha), and an untreated control. The treatments were arranged in a randomized complete block design with four replicates. Cantaloupe ‘Impac’ was seeded on 0.9 m raised beds at 0.6 m plant spacing. Nematicides were directly applied on planting beds and drip irrigated two weeks after seeding. At the end of cantaloupe crop, six soil cores were collected from 20 cm depth per plot and aliquots of 50-100 cm3 soil collected for soil microbial and nutrient analyses. Nematodes were extracted by Baermann Funnel Method and individual nematodes morphologically identified to genus level at x40-100 magnifications using an inverted microscope. Genomic DNA from bacteria and fungi was extracted and amplified targeting 16S rDNA or ITS regions and subjected to bioinformatics pipeline for metabarcoding. Soil samples were subjected to nutrient analysis to determine nitrogen (N), phosphorus (P), potassium (K), and soil organic matter (SOM) levels. Velum a xylem-translocated systemic nematicide significantly suppressed both RKN and beneficial nematodes bacterivores, fungivores and omnivores; thus, P and SOM levels were reduced highlighting its potential to compromise microbial activity and nutrient cycling. Velum being a fungicide also reduced fungal abundance. Majestene a bionematicide reduced bacterial and fungal abundance attributing to increased activity observed in bacterivores and fungivores, thus N and P levels were improved in the soil. Velum could be a good nematicide to control RKN. However, it may not be compatible with soil health as evidenced in negatively impacting soil microbiome and nutrient cycling. Majestene being an organic nematicide demonstrated its compatibility with soil health and improved soil microbiome and nutrient cycling. Different low risk nematicides react differently with rhizosphere microbiome.
Authors: Philip Waisen
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Philip Waisen Dr., University of California Cooperative Extension, California, 92211