Turfgrass (
Studying population changes of nematode functional groups can provide insight into potential effects of nematicides on soil health (Ferris et al., 2001). We conducted nematicide treatment programs in order to better understand potential non-target effects on non-herbivore free-living nematode community structure. We predicted nematicide applications would significantly affect nematode community structure by decreasing the number of nematodes belonging to high trophic levels and increased abundance from low trophic level nematodes.
Studies were conducted at the University of Florida Plant Science Research Unit (PSU) in Citra, FL. The study field was planted with ‘Tifdwarf’ bermudagrass and maintained with typical turfgrass management practices by the staff at PSU. The only chemicals used for maintenance were fertilizer, plant growth regulator, and herbicides. The field was treated as needed with thiencarbazone-methyl, foramsulfuron and halosulfuron-methyl, sulfentrazone, and trinexapac-ethyl for weed control and turf management. Plots were fertilized with a 13-4-13 controlled-release golf course green fertilizer during the growing season. Soil was 97% sand, 1% silt, 2% clay; 4% organic matter; pH 7.1.
The experiment used a randomized block design with five treatments and five replicates. In addition to an untreated control, the experimental treatments used were: abamectin (Divanem; Syngenta Crop Protection, Raleigh, NC), furfural (MultiGuard EC; Agriguard, Cranford, NJ), fluopyram (Indemnify; Bayer CropScience, Raleigh, NC), and fluensulfone (Nimitz Pro G; ADAMA Agricultural Solutions, Tel Aviv, Israel). Rates were based on the maximum allowable rate as listed on each label (Table 1).
Nematicide formulations used in the field study and their per-application labeled application rates.
Active Ingredient (a.i.) | Trade name | Application rate | Formulation |
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Abamectin | Divanem | 0.89 liters product/ha (70 g a.i./ha) | ECa |
Fluopyram | Indemnify | 1.25 liters product/ha (500 g a.i./ha) | EC |
Furfural | MultiGuard Protect | 56 liters product/ha (60 kg a.i./ha) 2016b
|
EC |
Fluensulfone | Nimitiz Pro G | 62.25 kg product/ha (1 kg a.i./ha) | G |
aEC, emulsifiable concentrate; G, granular. bLabeled rate changed between 2016 and 2017.
Applications of liquid treatments were made using a CO2-powered backpack sprayer (Weed Systems, Hawthorne, FL) with TJ-08 nozzles delivering 1,222 liters solution/ha. Nimitz Pro G was applied using a walk-behind Gandy (Owatonna, MN) drop-spreader. Plots were 6 m2 with 1.5 m2 data collection plots located in the center of each larger treatment plot to minimize any cross-contamination between plots. All plots were separated by an untreated 0.6 m border on each side. After each application, all treated and untreated plots were immediately irrigated with 0.64 cm of water. Treatments were applied every four weeks replicating a summer treatment program from June 7 to August 30 in 2016 and April 24 to July 18 in 2017.
Samples were collected prior to the initial treatment, and 2 d, 14 d, 56 d, and 238 d after the final treatment application (DAFT) each year. Turf plugs were collected using a 3.81-cm diameter ball mark plugger (Turf-Tec International, Tallahassee, FL) to a depth of 6.35 cm. Eight plugs were collected from the data collection subplots and combined in plastic sampling bags for analysis. The soil was shaken from the thatch and roots and nematodes were extracted from 100 cm3 of this soil by centrifugal flotation (Jenkins, 1964). Of the thatch and roots from the eight plugs, four were used for extraction of nematodes using mist extraction (Seinhorst, 1950). Turf plug extraction was performed separately from soil to target nematodes inhabiting the thatch layer that are not extracted as efficiently from soil (Crow, 2017). The remaining four plugs were used for arthropod extraction as part of a separate experiment. The misting chamber was a rectangular plexiglass structure containing PVC pipe running the length of the top plexiglass panel with misting nozzles arranged to provide a downward mist spray on the turf plugs. Nozzles were spaced 40 cm lengthwise and 30 cm widthwise along the length of the chamber. Funnels were placed 68 cm below nozzles in holes cut in a sheet of plexiglass to support each funnel. A mesh screen was placed on top of the funnel to support the turfgrass plugs. Mesh holes were 2 × 1 mm. Mist was sprayed on the samples for 45 sec every hour controlled by a solenoid valve (Hunter Industries, San Marcos, California) set on a recycling timer (Hydrofarm, Petaluma, California). Samples were collected in an Erlenmeyer flask below each funnel. Turfgrass plugs were left in the misting chamber for 72 hr and the collected specimens were preserved in 2% formalin and stored in plastic centrifuge tubes. Nematodes were identified morphologically and counted from soil and mist extraction samples using an inverted microscope (Olympus Corporation, Shinjuku, Tokyo, Japan). The primary guides used for nematode identification were Smart and Nguyen (1985) and Bongers (1988).
Data plots were photographed every two weeks using a digital camera mounted on a custom-built photo box throughout the growing period and continued until grass dormancy in the winter. Digital images were taken in center of data plots to be analyzed for the number of green pixels (hue 45–105, saturation 15–100) present in each image as a measure of turfgrass health using the macro developed by Karcher and Richardson (2005). Nematodes collected by mist and soil extraction were counted in gridded counting dishes using inverted microscopes. In total, 100 nematodes were identified from each sample, or the entire sample if the total number was fewer, to the family level.
Population counts were analyzed using analysis of covariance (ANCOVA) using R software version 3.3.2 (R Core Team, 2016). Data were log transformed to improve normality and homogeneity of variance. Population means of the different sampling dates were compared to the initial sample means using the untreated control as a covariate. ANCOVA was chosen to help account for natural seasonable variation. Nematode families were grouped into the feeding groups proposed by Yeates et al. (1993). Groups included were bacterivores, fungivores, herbivores, omnivores, and predators. The relative abundance of each feeding group was evaluated throughout the course of the two-year study. Data generated from both extraction methods were compared using a
In total, 24 nematode families were identified during the study. Of the families encountered, 6 families were categorized as plant-parasitic and 18 were categorized free-living. Nine of the families were bacterial-feeding, three were fungal-feeding, one was omnivorous, and five were predatory (Table 2). The bacterial-feeding family Cephalobidae was the dominant family representing 30% of all nematodes across both extraction processes. The dominant fungal-feeding family was Tylenchidae making up 18% of nematodes. Hoplolaimidae was the most abundant plant-parasitic group at 15% of total nematodes which was dominated by
Nematode families identified from turfgrass plugs and soil samples.
Family | Cp value | Proportion of total mist extracted nematodes | Proportion of total soil extracted nematodes | Proportion of total nematodes |
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Bathyodontidae | 4 | <0.01 | <0.01 | <0.01 |
Cephalobidae | 2 | 0.27 | 0.33 | 0.30 |
Diplogasteridae | 1 | <0.01 | <0.01 | <0.01 |
Diploscapteridae | 1 | <0.01 | <0.01 | <0.01 |
Diphtherophoridae | 3 | <0.01 | <0.01 | <0.01 |
Monhysteridae | 2 | <0.01 | <0.01 | <0.01 |
Plectidae | 2 | 0.01 | <0.01 | 0.01 |
Rhabditidae | 1 | <0.01 | 0.01 | 0.01 |
Teratocephalidae | 3 | <0.01 | 0.01 | 0.01 |
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Anguinidae | 2 | <0.01 | <0.01 | <0.01 |
Aphelenchidae | 2 | 0.05 | 0.02 | 0.03 |
Tylenchidae | 2 | 0.28 | 0.10 | 0.18 |
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Aporcelaimidae | 5 | 0.08 | 0.17 | 0.13 |
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Discolaimidae | 5 | <0.01 | <0.01 | <0.01 |
Ironidae | 4 | <0.01 | <0.01 | <0.01 |
Monochidae | 4 | 0.00 | <0.01 | <0.01 |
Qudsianematidae | 4 | 0.08 | 0.02 | 0.04 |
Thornenematidae | 5 | <0.01 | 0.01 | 0.01 |
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Belonolaimidae | 3 | <0.01 | 0.02 | 0.03 |
Criconematidae | 3 | <0.01 | 0.01 | 0.01 |
Heteroderidae | 3 | 0.10 | 0.05 | 0.08 |
Hoplolaimidae | 3 | 0.08 | 0.20 | 0.15 |
Longidoridae | 5 | 0.02 | <0.01 | 0.01 |
Trichodoridae | 4 | <0.01 | <0.01 | <0.01 |
Bacterivores in abamectin-treated plots increased at 238 d after final treatment (DAFT) relative to the untreated control (
Population densities of bacterivore nematodes from mist and soil extraction as affected by different nematicide applications at all sampling dates. *,**,***Different from the untreated according to analysis of covariance,
Abamectin-treated plots had reductions in fungivores (
Population densities of fungivore nematodes from mist and soil extraction as affected by different nematicide applications at all sampling dates. *,**,***Different from the untreated according to analysis of covariance,
Fluopyram reduced omnivore population densities relative to the untreated control (
Population densities of omnivore nematodes from mist and soil extraction as affected by different nematicide applications at all sampling dates. The scale of the y-axis for soil extraction is different for 2017 than for 2016. *,**,***Different from the untreated according to analysis of covariance,
Abamectin reduced predator abundance relative to the untreated control (
Population densities of predatory nematodes from mist and soil extraction as affected by different nematicide applications at all sampling dates. *,**,***Different from the untreated according to analysis of covariance,
Abamectin lowered MI relative to the untreated control (
Maturity index (MI) from mist and soil extraction as affected by different nematicide applications at all sampling dates. *,**,***Different from the untreated according to analysis of covariance,
Abamectin-treated plots had significant reduction in EI compared to the untreated control (
Data points from all plots prior to the first treatment were clustered in quadrats C and B from ME and all in quadrat C from SE. Data points migrated from quadrat C to being divided between quadrats D and C over the course of the study. Environmental conditions shifted from a highly structured, moderately enriched environment to a low structure, low enrichment environment. Enrichment and structure indices calculated from abamectin, furfural, and fluensulfone plots were not different from untreated control at the same date from either extraction method (
Photograph data were analyzed from 38 time points across the two-year study (data not shown). All four nematicides significantly affected percent green coverage (
Abamectin had intermediate effects on nematodes, altering the community structure of free-living nematodes and causing disturbance to the soil ecosystem as indicated by a shift to a slightly less mature soil food web. Effects on nematodes were generally detected later in the season and could be explained by the characteristic slow movement of this formulation through the thatch layer of turfgrass (Gannon et al., 2017). High cp nematodes were mildly affected by abamectin. The reduction in higher trophic nematodes at the later sampling dates was accompanied by bacterivore increases at a few dates; possibly influencing the trophic cascade by reducing pressure of predatory nematodes on bacterivores (Wardle and Yeates, 1993). The enrichment index did not indicate an enriched environment; however, this index considers both bacterivore and fungivore abundance and could be offset by the reduction in fungivores belonging to the cp-2 class. Maturity index and structure index values suggested abamectin plots had a basal environment with reduced abundance of high trophic nematodes at the end of the study. Abamectin had a positive effect on turfgrass health as measured by percent green coverage, which is an important consideration.
While the nematicidal properties of avermectin family members have been known for some time, few studies have considered the effects of abamectin or ivermectin on free-living nematodes (Brinke et al., 2010; Bai and Ogbourne, 2016). Ivermectin contained in feces from cattle treated for animal-parasitic nematodes has been shown to affect
Fluopyram had the most striking results of the nematicides tested. It reduced numbers of both beneficial nematode and plant-parasitic nematodes at intermediate and long-term sampling intervals in both years. Bacterivores, fungivores, and omnivores were susceptible to fluopyram at most sampling dates and predators were reduced at intermediate and late sampling dates. These observations suggest fluopyram has the potential to affect all nematode feeding groups quickly after application and throughout the season. Fungal feeders were not significantly affected. EI values revealed an enriched environment after fluopyram application on a couple dates. In addition to the reduction of nematode functional group densities, a shift occurred toward an environment dominated by
Furfural had a low impact on free-living nematodes. The fungivore and predatory nematode functional groups were the only feeding groups negatively affected by furfural. The general lack of reduction in functional group densities suggests furfural may have low risk to free-living nematodes. No adverse effects on free-living nematodes were observed, which support results obtained by Abdelnabby et al. (2016, 2018), although negative impacts on bacterivore and fungivore nematodes from furfural have been documented in tomato field trials (Ntalli et al., 2018). Plant-parasitic nematodes increased at two-week sampling dates in one year (data not shown). These results may be attributed with temporary
Fluensulfone had low impacts on free-living nematodes comparable to furfural. Fungivores were the only functional group negatively affected at one sampling date in 2017. Predators increased in abundance at eight weeks in both years. As a result, structure and food web complexity were greater in fluensulfone-treated plots than untreated control according to the maturity indices and SI. Laboratory-based assays have found the plant-parasite
In summary, nematicides can negatively impact free-living nematodes in bermudagrass. Fluopyram had the greatest impacts on nematode functional groups followed by abamectin in this study. Despite the negative effects on free-living nematodes, turfgrass percent green cover was generally higher in both fluopyram and abamectin plots. Furfural and fluensulfone had low impacts on free-living nematodes, but low impacts on turfgrass green cover were also observed. Nematicides are used to reduce the impact of plant-parasitic nematodes and it is, therefore, expected that nematicides with greater efficacy tend to have greater impact on nematode community structure.
Our hypothesis that “nematicide applications would significantly affect nematode community structure by decreasing the number of nematodes belonging to high trophic levels and increased abundance from low trophic level nematodes” was only partially supported. Our results show that the nematicides with the greatest impact, fluopyram, reduced numbers of both high and low cp nematodes. Therefore, the effects of nematicides on faunal profile were minimal because all trophic groups were impacted similarly.
While there were significant impacts from the treatments, it should not be assumed that they were all due to direct effects of the chemicals. For example, some treatments resulted in healthier grass than other treatments, and plant health can drive an ecosystem. Similarly, the treatments might affect arthropods, fungi, bacteria, etc., that are predators, pathogens, or food for different types of nematodes and influence the nematode community structure that way. Finally, while the treatments were all applied according to their labels, their application rates and timing may not reflect how they would be recommended for use in the field. For research purposes, they were all applied on the same schedule using the maximum rate allowable. However, a golf course might make fewer applications, space out treatments at different times of the year, apply lower rates than the maximum, or rotate chemistries. The objective of this research was not to indicate that certain nematicides were better than others. Rather, the intent was to introduce the concept of soil ecosystem health into the discussion of golf course nematode management and to promote further research into nematode integrated pest management.