Investigating population dynamics of Hoplolaimus galeatus and select associated relationships in creeping bentgrass putting greens

Abstract

Hoplolaimus galeatus, a prevalent lance nematode, is increasingly problematic in U.S. turfgrass due to product restrictions and ineffectiveness. These studies aim to quantify the relationship between creeping bentgrass health and nematode populations, and to evaluate a qPCR diagnostic method. Plant growth regulators (PGRs) are used to optimize turfgrass growth and reduce management inputs, but anecdotal evidence suggests a link between increased PGR-induced phytotoxicity and high populations of lance nematodes One study investigated the relationship between PGR usage and lance nematode populations on creeping bentgrass putting green health during summers in the Mid-Atlantic United States. Five levels of PGR and the presence or absence of fluopyram were studied across six site-years. Data suggests that elevated lance nematode populations typically do not exacerbate damage to creeping bentgrass caused by PGR applications, though injury in plots treated with prohexadione calcium was more pronounced with high lance nematode populations in some instances. Management of lance nematodes on creeping bentgrass often relies on lab assay recommendations but counts exceeding thresholds do not always coincide with visible damage. A greenhouse study examined the relationship between lance nematode populations and creeping bentgrass root biomass using inoculated nematode populations and varying levels of nitrogen to promote root growth. Increased nematode populations reduced root biomass (r= -0.56322), though increasing nitrogen inputs led to higher nematode counts without affecting root biomass. This relationship suggests the need for a modified root biomass-based threshold, though further evaluations and improved quantification techniques are warranted. Methods using qPCR were adapted to identify and quantify lance nematodes in golf course putting greens. Manual counts of lance nematodes from field plots were compared to qPCR cycle threshold values, showing a weak negative relationship (r= -0.39956) between DNA quantity and these counts. This relationship was improved by refining sources of error using handpicked samples of 20, 50, 100, and 250 lance nematodes (r= -0.75695). Collectively, these studies enhance our understanding of lance nematode and creeping bentgrass putting green dynamics. Lance nematodes typically did not negatively impact PGR usage, except when prohexadione calcium was used on stressed creeping bentgrass with lance populations. Our data reiterates that high lance populations negatively influence root biomass, and that adding nitrogen may increase these populations.