Article Category: Arts & Humanities
Published Online: Jul 31, 2019
Page range: 1 - 8
Received: Dec 28, 2018
DOI: https://doi.org/10.21307/jofnem-2019-045
© 2019 Travis R. Faske et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
The southern root-knot nematode,
Nematicides continue to be an important part of an integrated system to manage root-knot nematodes in cotton and soybean. They are most often utilized when
Fluopyram is classified as a succinate dehydrogenase inhibitor fungicide that is used extensively as a seed- and soil-applied nematicide in cotton and soybean. Fluopyram has been reported to be toxic to several species of plant-parasitic and free-living nematodes (Faske and Hurd, 2015; Heiken, 2017; Beeman and Tylka, 2018). However, suppression of
The objectives of this study were to evaluate the effect of soil texture and soil water infiltration rate on the movement of soil-applied fluopyram, and to evaluate the movement of fluopyram from treated cotton and soybean seed.
Cotton cv. Stoneville ST 4747 GLB2 with commercially applied seed treatments were used in this study. All cotton seed were treated with a base fungicide treatment of metalaxyl + penflufen + prothioconazole + mycolbutanil (Allegiance® FL + EverGol® Prime + Proline® 480 SC, Bayer CropScience, Research Triangle Park, NC and SperaTM 240 FS, Nufarm Americas Inc., Alsip, IL) at 0.015+0.005+0.005+0.003 mg ai/seed, respectively. Seed-applied nematicide and insecticide treatments consisted of imidacloprid + thiodicarb (Aeris® Seed-Applied Insecticide/Nematicide, Bayer CropScience, Research Triangle Park, NC) at 0.75 mg ai/seed, abamectin (Avicta® 500 FS, Syngenta Crop Protection, Greensboro, NC) at 0.15 mg ai/seed + thiamethoxam (Cruiser® 5 FS, Syngenta Crop Protection, Greensboro, NC) at 0.34 mg ai/seed, and fluopyram (COPeO® Prime, Bayer CropScience, Research Triangle Park, NC) at 0.25 mg ai/seed + imidacloprid (Gaucho® 600 FS, Bayer CropScience, Research Triangle Park, NC) at 0.375 mg ai/seed.
Soybean cv. Hornbeck HBK RY4721 with commercially applied seed treatments were used in this study. All soybean seed were treated with a base fungicide treatment of prothioconazole + penflufen + metalaxyl (EverGol® Energy SB, Bayer CropScience, Research Triangle Park, NC) applied at 0.02 mg ai/seed. Seed-applied nematicides and insecticides consisted of clothianidin +
Four experiments were conducted to evaluate the movement of fluopyram as a water dilution in soil columns with different soil types, water infiltration rates, and soil volume. Soil columns were constructed by filling a plastic tube (6-mm-diam.×160-mm-long) with <2.0-mm-diam. sterilized sandy soil (100% sand; pH 6.7; CEC 2.0 cmol+/kg) and wetted to field capacity by applying a total of 1.8 ml sterilized distilled water. To each column, 25.0 µg of agricultural grade fluopyram (Velum® Prime, Bayer CropScience, Research Triangle Park, NC) in 100 µl of distilled water was applied on the soil surface and incubated overnight (16 hr) in a resealable plastic bag. The concentration of fluopyram used is estimated to be 10% of that used on cotton seed and the liquid formulation of fluopyram + imidacloprid used in cotton. Agricultural grade abamectin (Avicta® 500 FS, Syngenta Crop Protection, Greensboro, NC) at 25.0 µg was used as the industry standard and distilled water as a negative control. Soil columns were drenched with 0.12 µl water/mm3 soil at a base rate of water infiltration of 20.0 mm/d on day two and incubated overnight in a resealable plastic bag. Plastic tubes were cut into 5-cm-long segments on day three and the soil within each segment dislodged into a 5-ml centrifuge tube (Eppendorf Ag, Hamburg, Germany) that contained 1 ml sterilized distilled water and vortexed for 30 sec. The supernatant was used immediately in a nematode motility bioassay. These bioassays were performed in 24-well Falcon tissue cultures plates (Corning Life Science, Tewksbury, MA). Each well received 500 µl of supernatant from a single centrifuge or conical tube, which contained 30 to 40 J2 in 500 µl of distilled water and incubated at 28°C for 24 hr. Second-stage juvenile motility was determined visually with an inverted compound microscope (Axio Vert.A1, Carl Zeiss Microscopy, Thornwood, NY). Nematodes were considered dead if they did not respond to being touched by a small probe and the percent of dead nematodes were recorded. Treatments were arranged in a completely randomized design (CRD) with three replications and the experiment was conducted three times.
To evaluate the effect of soil texture on fluopyram movement, plastic tubes (6-mm-diam.×160-mm-long) filled with <2.0-mm-diam. sterilized sandy loam soil (62% sand, 30% silt, and 7% clay; <1% organic matter; pH 6.0; CEC 11.3 cmol+/kg) were used in the second experiment. Methods used were the same as described in the first experiment with the exception of 1.9 ml water used to wet soil to field capacity and that 5-ml tubes were centrifuged at 25,000 RPM for 3 min to remove some silt and clay particles from the supernatant to better visualize nematodes in bioassay. Treatments were arranged in a CRD with three replications and each experiment was conducted three times.
The effect of a slower rate of water infiltration on fluopyram movement was investigated in the third experiment. Soil columns were constructed with sandy soil and nematicide treatments applied as described in experiment one. A slower rate of water infiltration was achieved by applying the same water volume (0.12 µl water/mm3 soil) in 20 µl aliquots most days over a 30-day period. Methods for supernatant collection and nematode bioassay were as described previously. Treatments were arranged in a CRD with three replications and each experiment was conducted three times.
The movement of soil-applied fluopyram was evaluated in a larger volume of soil in the fourth experiment. Soil columns were constructed by filling a plastic tube (12-mm-diam.×160-mm-long) with sandy soil (100% sand) and wetted to field capacity with 5 ml distilled water. Nematicide treatments and methods used were as described in experiment one. Soil columns were drenched with 0.12 µl water/mm3 soil at a base rate of water infiltration of 20.0 mm/d on day two and incubated overnight in a plastic bag. Plastic tubes were cut into 5-cm-long segment on day three and the soil within each segment was dislodged into a 15-ml conical tube that contained 5 ml sterilized distilled water and vortexed for 30 sec. Supernatant was used immediately in a nematode motility bioassay, described previously. Treatments were arranged in a CRD with three replications and the experiment was conducted twice.
Two experiments were conducted to evaluate the movement of fluopyram from the seed coat of cotton and soybean seed. Soil columns (6-mm-diam.) were constructed with sandy soil as described previously. Fluopyram-treated cotton seeds were placed 2.0 cm below soil surface and incubated overnight in a resalable plastic bag. Other seed-applied nematicide treatments consisted of imidacloprid + thiodicarb and abamectin. Fungicide-treated cotton seed served as the negative control. Methods for water drench (base rate of water infiltration), supernatant collection, and nematode bioassay were as described previously for 6-mm-diam. soil column. Treatments were arranged in a CRD with three replications and the experiment was conducted twice.
In the second seed-applied nematicide experiment, fluopyram movement from soybean seed was investigated. Twelve-mm-diameter soil columns were constructed with sandy soil as described previously. The larger column was used to accommodate the larger soybean seed. Fluopyram-treated soybean seeds were placed 2.0 cm below soil surface and incubated overnight in a resalable plastic bag. Other seed-applied nematicide treatments consisted of clothianidin +
Percent nematode mortality data were arcsine transformed (arcsine (sqrt(
There was no (
Figure 1:
Percent dead
In the second experiment with sandy loam soil and base rate of water infiltration, a greater (
In the third experiment with sandy soil and a slower rate of water infiltration, a similar effect on nematode activity was observed at 0 to 5 cm soil depth with 97 and 94% J2 mortality for fluopyram and abamectin, respectively (Fig. 2A). However, a greater (
Figure 2:
Percent dead
In the fourth experiment with sandy soil, base rate of water infiltration, and a larger (12-mm-diam.) soil column, a similar effect on nematode activity were observed at 0 to 5 and 6 to 10 cm soil depth with an average J2 mortality of 87% for abamectin and 91% for fluopyram (Fig. 2B), while there was no effect on nematode activity beyond the 10 cm soil depth. Similar results were observed with that of the 6-mm-diam. soil column and base rate of water infiltration in the first experiment.
In the seed-applied nematicide experiments, there was no (
Figure 3:
Percent dead
Nematicide movement from soybean seed was similar for abamectin and fluopyram at 0 to 5 cm soil depth as indicated by 49 and 34% J2 mortality, respectively (Fig. 3B). Both nematicides had a greater (
These data indicate that the downward movement of the nonfumigant nematicide, fluopyram, is affected by soil type and application method. This may account for difference in the field efficacy of fluopyram that have been reported. Most of the fluopyram and abamectin in sandy loam soil remained in the upper 5 cm soil depth, while in sandy soil moved slightly deeper, but remained in the upper 10 cm soil depth. Similar results were reported with avermectin B1a, one of the main (80%) components of abamectin, where 90% of the abamectin remained in the upper 6 cm of a soil column filled with sandy loam soil (Gruber et al., 1990). The movement of other nonfumigant nematicides and insecticides were reported to be limited in soils with small pore spaces and fine particle sizes (Harris, 1972; Bromilow, 1973; Whitehead, 1973). Thus, fluopyram may be less effective in finer textured soils.
A slower rate of water infiltration had less impact on the movement of fluopyram than on abamectin. Strongly adsorptive compounds such as abamectin are less mobile, while weakly adsorbed compounds are more easily distributed in soil by water infiltration (Smelt and Leistra, 1992). Abamectin has very low mobility, very low water solubility (0.0078 mg/L) and a high soil adsorption coefficient (4,000-5,000 ml/g), while fluopyram has moderate mobility, low water solubility (16.0 mg/L) with a lower soil adsorption coefficient (233-440 ml/g) (Wislocki et al., 1989; Wauchope et al., 1992; ESFA, 2013). It is generally accepted that some water infiltration is necessary to distribute nonfumigant nematicides beyond the point of application (Bromilow, 1973). In preliminary experiments (data not shown), water was necessary to distribute seed- and soil-applied fluopyram beyond 5 cm soil depth in sandy soil. Based on nematode motility neither fluopyram nor abamectin was detected at nematode-toxic levels beyond 10 cm depth in sandy soil. Although the mobility of abamectin is low it is more toxic to
The concentration of fluopyram and abamectin detected from treated cotton and soybean seed was greater in the upper 5 cm soil depth with less detected at other soil depths. In general, seed-applied abamectin and fluopyram had a lower effect on
In comparison between seed types, in general, the concentration of fluopyram and abamectin detected at 0 to 5 and 6 to 10 cm soil depth from cotton seed contributed to a greater percentage of J2 mortality than that from soybean seed. Although more fluopyram was applied on cotton seed (250 µg/seed) than soybean (150 µg/seed), both seeds were treated with the same concentration of abamectin (150 µg/seed). Further, based on the known concentration response [
Of the other seed-applied nematicides tested, none had an effect on nematode motility. Carbamate nematicides like thiodicarb have been reported to vary in their effect on
The movement of fluopyram was greater in sandy soil as a soil-applied treatment with reductions in movement in a sandy loam soil or as a seed-applied treatment. This study supports the importance of the soil texture and physical properties of nematicides when investigating nematicide efficacy and provides a better understanding as to the downward movement of seed- and soil-applied fluopyram in sandy soil.