Taking a look at a new option for nematode management in turfgrass

Photo 1. Belonolaimus longicaudatus (sting nematode) is a large nematode, reaching sizes of about 1/8-inch long when mature. (Photo: Bruce Martin)

Plant-parasitic nematodes are a significant pest of turfgrass in the U.S., yet there are few options for successful management. Most current management strategies rely on using a limited number of chemical nematicides, so finding a new management option for nematode suppression would be extremely valuable for turfgrass managers.

One potentially helpful chemical nematicide for turfgrass is fluazaindolizine (Reklemel, Corteva Agriscience), a novel sulfonamide recently discovered to have nematicidal properties (5,6,7).

Effectiveness in specialty crops

Assessments of Reklemel in vitro show its ability to significantly reduce the motility and activity of Meloidogyne incognita (root-knot nematode) juveniles compared to untreated juveniles. Greenhouse assays of Reklemel on tomatoes have lowered root-knot reproduction (8). In similar research, Reklemel reduced root gall index, eggs per gram of root and nematode reproductive factor in tomatoes compared to an untreated control (3).

Reklemel was also effective as a nematicide treatment over a multi-year field study on root-knot nematode in carrots (1). Reklemel effectively reduced the root gall index and root-knot nematode population density and provided a consistent yield increase compared to an untreated control in cucumber trials (4).

With such a limited number of chemical nematicide options available for plant-parasitic nematode management on turfgrass, Reklemel would be a beneficial addition for nematode management.

Photo 2. Sting nematode has a long stylet that allows it to feed deep within root tissues. (Photo: Bruce Martin)

Materials and methods

We evaluated three rates of Reklemel to reduce both root-knot (Meloidogyne incognita) and sting nematode (Belonolaimus longicaudatus) nematode population density throughout the study. We included fluopyram (Indemnify; Bayer CropScience) as a chemical control and an additional tap water treatment as a negative control.

Treatments for the experiments were:

1. Four applications of Reklemel (fluazaindolizine) at a rate of 1 lb. per acre at 0, 4, 8, and 12 weeks after trial initiation
2. Two applications of Reklemel at a rate of 2 lbs. per acre on weeks 0 and 8
3. One application of Reklemel at a rate of 4 lbs. per acre on week 0
4. Two applications of fluopyram at 0.22 lbs. per acre on weeks 0 and 8
5. An application with an untreated tap water control

We conducted separate research trials on bermudagrass infested with root-knot and sting nematode in field settings in 2018 and 2019. In 2018, our field trial for sting nematode was on infested common bermudagrass grown under fairway conditions at the Auburn University Gulf Coast Research and Extension Center (GCREC) in Fairhope, Ala.

We conducted separate research trials on bermudagrass infested with root-knot and sting nematode in field settings in 2018 and 2019. In 2018, our field trial for sting nematode was on infested common bermudagrass grown under fairway conditions at the Auburn University Gulf Coast Research and Extension Center (GCREC) in Fairhope, Ala.

In 2019, we conducted two field trials evaluating Reklemel as a turfgrass nematicide. We conducted trials at GCREC in the same location as in 2018 for sting nematode evaluations and an adjacent location with a confirmed population density of root-knot nematodes (Meloidogyne spp). The treatment list remained the same as in previous studies for both nematode trials.

(Fig. 1) Sting nematode (Belonolaimus longicaudatus) population density in 2018 (A) and 2019 (B) and root-knot nematode (Meloidogyne incognita) population density in 2019 (C) as affected by treatments in nematicide trials at Fairhope, Ala. Nematicide rates were applied as: Reklemel (fluazaindolizine) 1 pound per acre at weeks 0, 4, 8, 12; 2 pounds per acre at weeks 0, 8; 4 pounds per acre at week 0; fluopyram 0.22 pounds per acre at weeks 0, 8.
*Different from the untreated according to the pairwise comparison of each treatment to the untreated control (Tukey–Kramer; P ≤ 0.05).

Field data collection

We took visual turfgrass ratings and NDVI values with a handheld sensor at the start of the experiment, followed by approximately two-week intervals throughout the trial as previously described. Along with these measurements, we mapped field trials with a DJI Phantom 4 Pro, equipped with a MicaSense RedEdge-M sensor.

We used Pix4D mapper for image processing and ArcMap for image analysis, providing NDVI and NDRE ratings for each plot. Nematode samples were taken three times in 2018 (Aug. 7, Sept. 4 and Oct. 2) and four times in 2019 (July 25, Aug. 22, Sept. 24 and Oct. 23), approximately at four-week intervals.

For nematode sampling, we used seven 0.875-inch-by-4-inch deep cores from each plot, thoroughly mixed. We extracted nematodes from a 40 cubic inch subsample and enumerated them as previously described.

Statistical analysis

To analyze data collected from field evaluations, we used the PROC GLIMMIX procedure (SAS version 9.4, SAS Institute). Dependent variables included each nematode per 100 cm3 soil, visual turf quality and NDVI. The fixed effect was nematicide treatment, and random effects included replication, test repeat and location.

Results and discussion

For both 2018 and 2019 field evaluations, nematicide treatments significantly impacted plant-parasitic nematode population density (Figure 1). However, we did not observe visual symptoms in the trial. Thus, we reported no significant differences for visual ratings, handheld NDVI, or drone NDVI and NDRE values for either year (data not shown).

In 2018, the 4 pounds per acre rate of Reklemel and the two 0.22 pounds per acre of fluopyram significantly reduced sting nematode population density at the September and October sample dates. The 2 pounds per acre rate of Reklemel significantly reduced population density at the October sample date (P ≤ 0.05).

In both the sting and root-knot nematode 2019 field trials, three of the four nematicide treatments significantly reduced nematode population density compared to the untreated control at the August evaluation date (Figure 8, B and C). All nematicides significantly reduced nematode population density at the September and October evaluation dates (P ≤ 0.05).

Results

The results from both years’ field evaluations of Reklemel indicate a strong potential for its use in plant-parasitic nematode management in turfgrass. The plant-parasitic nematode population density was significantly lower compared to an untreated control. These significant population declines reduced sting and root-knot nematode numbers below the standard 10 and 80 per 100 cm3 of soil.

Field trials showed substantial reductions in both sting and root-knot population density by Reklemel. While all nematicide rates and applications led to nematode population density reduction, the medium and high rates of Reklemel and Indemnify most consistently lowered population density across all trials.

Despite confirming strong population density for both sting and root-knot nematodes at the field sites for these trials, we did not observe visual symptoms. Thus, while the higher rates of Reklemel again had substantial impacts on nematode density, we cannot substantiate the effect of Reklemel on plant vigor in the field setting.

Our research confirms previous studies that have shown a similar efficacy of Reklemel to root-knot nematode for reducing population density on crops including cucumber, carrot and tomato (1,3,4).

While Meloidogyne incognita is pathogenic to bermudagrass, it is not traditionally the main Meloidogyne species identified on turfgrass in the Southeast (2,9,10). We used M. incognita for this research because all research plots were inoculated to obtain infested turfgrass, and M. incognita was available at a high enough population density for successful inoculation.

In the future, evaluations need to include field locations with species more commonly found on turfgrass (M. graminis and M. marylandi) to confirm the findings of this study. To our knowledge, this is the first published study on Reklemel’s (fluazaindolizine) efficacy as a turfgrass nematicide.

While these results show promise for this product, more research is needed. Overall, fluazaindolizine appears to have strong potential for inclusion in a turfgrass nematode integrated management program.