Integrated management strategies for plant-parasitic nematodes on warm-season turfgrass using plant growth-promoting rhizobacteria, chemical nematicides, and remote sensing technology
Type of DegreePhD Dissertation
Entomology and Plant Pathology
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Plant-parasitic nematodes are a major pathogen of turfgrass throughout the United States, yet management strategies rely almost entirely on a limited number of chemical nematicides. The overall objective of this research was to gain a deeper understanding of how plant-parasitic nematode population dynamics are impacted by seasonal changes in Alabama, and to evaluate multiple strategies for managing these nematodes in turfgrass when population density reaches damaging levels. Management practices evaluated in these studies include evaluating a new chemical nematicide for its ability to reduce nematode population density, using PGPR to suppress nematode population density while also promoting root growth, and combining remote sensing technology with chemical nematicides to help standardize rating assessments of plant-parasitic nematode infested turfgrass. Chapter I is a detailed review of literature related to turfgrass and how plant-parasitic nematodes influence its growth and development. This review gives details on the importance of turfgrass from an economic perspective, as well as provides information on its biology. An in-depth analysis is also provided on the numerous genera of plant-parasitic nematodes that can impact turfgrass, including the differences in turfgrass host range, population density levels, and damage potential. Current and potential management strategies for plant-parasitic nematodes are also discussed. In Chapter II, a survey was conducted of six highly maintained bermudagrass sites in Alabama. Monthly or bimonthly sampling was conducted at each site over 2018 and 2019 to identify which plant-parasitic nematode genera were present, and if there are any seasonal differences in population density. Over both years, seven plant-parasitic nematode genera were identified: Belonolaimus, Helicotylenchus, Hemicycliophora, Hoplolaimus, Meloidogyne, Mesocriconema (sensu lato), and Tylenchorhynchus (sensu lato). Of these seven genera identified, only two were ever found at potentially damaging levels: Belonolaimus and Meloidogyne. Interestingly, highest population density of Belonolaimus was found in April and October, and conversely, highest population density of Meloidogyne was found during midsummer (June through September). These results indicate that nematode genera are influenced by seasonality in turfgrass. This data also reinforces the importance for Alabama turfgrass managers to sample for nematodes throughout the year, and not rely on one sample date for management decisions. In Chapter III, the chemical nematicide reklemel was evaluated for its efficacy as a potential option for plant-parasitic nematode management on turfgrass. This product was screened against B. longicaudatus and M. incognita on bermudagrass in greenhouse, microplot, and field settings. In the greenhouse, reklemel significantly reduced B. longicaudatus population density compared to the untreated control in both evaluation trials, and significantly reduced M. incognita population density in one of the two evaluation trials. In the microplot setting, reklemel was effective at lowering population density against both B. longicaudatus and M. incognita in all trials during the 2018 and 2019 growing seasons. Reklemel also led to an improvement of visual turfgrass quality and NDVI ratings compared to the untreated plots. A negative correlation was also observed between both visual turfgrass ratings and NDVI with nematode population density at multiple sample dates, showing that as reklemel reduced nematode population density, turfgrass quality improved. In the field setting, the higest rate of reklemel was most effective at lowering the population density of both B. longicaudatus and M. incognita, but no significant differences in visual quality or NDVI ratings were ever observed. Overall, reklemel shows promise as a chemical nematicide for plant-parasitic nematode management on turfgrass. The primary research objective for Chapter IV was to evaluate the ability of plant growth-promoting rhizobacteria (PGPR) for their nematicidal ability against M. incognita, while potentially also promoting bermudagrass root growth. In this study, 104 PGPR strains were evaluated for their ability to manage M. incognita in vitro. In vitro mortality of M. incognita ranged from 0.9 to 98.9%, and ten individual PGPR strains and one three-strain blend were advanced to greenhouse and microplot screening. In a greenhouse, seven of the eleven PGPR treatments significantly lowered M. incognita population density compared to the untreated control, with a couple strains also promoting root growth. In a microplot evaluation, five of the eleven PGPR treatments significantly reduced M. incognita population density. Between the greenhouse and microplot trials, three PGPR strains significantly reduced M. incognita population density compared to the untreated control. These were Stenotrophomonas rhizophila and two strains of Bacillus aryahbatti. Overall, these results indicate that multiple PGPR strains evaluated have the potential to reduce M. incognita population density on infected turfgrass. Finally, in Chapter V, remote sensing technology was evaluated for the abilty to track the plant health of plant-parasitic nematode infested turfgrass in combination with chemical nematicides. For this study, the chemical nematicides abamectin, fluensulfone, fluopyram, and furfural were evaluated over two years in microplot trials for their ability to reduce both B. longicaudatus and M. incognita on bermudagrass. During these trials, visual turfgrass quality ratings were taken as well as NDVI and NDRE values. In both years of data, visual turfgrass quality, NDVI and NDRE were found to be strongly correlated with plant-parasitic nematode population density: as plant-parasitic nematode population density declined, turfgrass vigor ratings improved. This study was also taken to a golf course infested with multiple genera of plant-parasitic nematodes in 2019. In this study, the nematicides abamectin, fluensulfone, and fluopyram were evaluated for their ability to reduce plant-parasitic nematode density, as well as their ability to impact visual turfgrass quality, NDVI, and NDRE. Similarly to the microplot evaluations, as nematode population density declined, all evaluation parameters improved. These results indicate that using NDVI and NDRE data in conjunction with visual turfgrass quality ratings provides a strong foundation for capturing the ability of currently available chemical nematicides to manage plant-parasitic nematodes on turfgrass.