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Soil Health and Nematode Response to Integrating Sudan Grass Rotation and Reduced-Risk Nematicides on Carrot in Southern Desert Valleys of California

Agronomy & Pest Management

Philip Waisen
UCCE Riverside
Palm Desert


In southern desert valleys of California, carrot (Daucus carota) and Sudan grass (Sorghum × drummondii) are economically important crops. Planting and harvesting dates of these crops naturally permit to grow in rotation. As a rotation crop, Sudan grass can reduce common nematode parasites of carrots through non-host, allelopathy, and soil health improvement. Cultivation of Sudan grass and incorporation of its residues, after cutting hay, enriches the soil with nutrients and adds organic matter to stimulate bacterial and fungal activity in the soil. Because soil health is a function of microbial activity, changes in soil health conditions can be reflected on the demographic shift in microbivorous nematodes such as bacterial, fungal, omnivorous, and predatory nematodes. Integrating reduced-risk nematicides with selective mode of action could suppress nematode pests that survive preceeding crop rotation. A field trial was conducted at the end of Sudan grass crop in Fall of 2022 to examine the soil health and nematode response to integrating Sudan grass rotation and reduced-risk nematicide treatments. Sudan grass residue was incorporated after cutting hay. Two weeks after seeding carrot, Salibro™ (fluazaindolizine) and Velum® One (fluopyram) nematicides were applied at 31.0- and 13.6 fl oz/ac, respectively, on 60-inch seed beds using an SRS Sprayer. An untreated control treatment was included and each treatment was replicated 4 times in a randomized complete block design. For nematode assays, soil samples were collected before nematicide treatment and at monthly intervals thereafter. Abundance of plant-parasitic nematodes was low to start with at the end of Sudan grass and remained low thereafter, an indication of the benefit of Sudan grass rotation. Improvement of soil health conditions by Sudan grass or as a non-host crop could have antagonized parasitic nematodes. Velum nematicide treatment negatively impacted soil health as reflected on the abundance of beneficial nematodes. Salibro treatment, however, had no impact on these beneficial nematodes. The effect of Velum was non-discriminatory on both beneficial and parasitic nematodes. This suggests that soil health benefits of Sudan grass can be compromised by Velum. In contrast, integrating Sudan grass with Salibro is a promising option.

Authors: Philip Waisen
  1. Philip Waisen Vegetable Crops Advisor, University of California Cooperative Extension, California, 92201