Meloidogyne incognita management by nematicides in tomato production

To test these objectives, three field trials (2018, 2019, and 2020) were conducted at the University of Florida North Florida Research and Education Center-Suwannee Valley located near Live Oak, FL (30°18′07.6″ N, 82°54′03.3″ W). The soil was a Chipley–Foxworth–Albany complex (91% sand-6.8% silt-2.4% clay; 1.6% organic matter).

A preliminary experiment to test the efficacy of nematicides against SRKN was conducted in 2018. The experiment was a randomized complete block design with five replicates. The nematicide treatments included 1,3-dichloropropene (1,3-D) and fluopyram combinations as described in Table 1. The 1,3-D was applied in the form of Telone II (Corteva Agrisciences, Wilmington, DE). The 1,3-D was applied to flat ground as a broadcast treatment 22 days before planting (DBP) using a shank fumigation rig. The rig was configured with five coulters to open traces immediately in front of the five shanks with press wheels behind each shank to seal traces. Shanks were spaced at 30–cm intervals for a total application band of 2.03 m, and nematicide was released at 25–cm deep in the soil profile.

Fluopyram was applied as Velum Prime (Bayer Cropscience, Research Triangle Park, NC) by chemigation at transplanting or 21 days after planting (DAP) depending on treatment as described in Table 1. Fluopyram was chemigated through a single, surface drip tape per plot. Plots with the same treatment were plumbed through a common irrigation line. Irrigation was applied for 10 min before any nematicides were applied. Fluopyram was then applied through irrigation lines for approximately 10 min using a Masterflex L/S (Cole Parmer, Vernon Hills, IL) multi-line pump with one line per treatment. After nematicide injection, irrigation was applied for approximately 10 additional minutes to incorporate nematicide into the soil. Emitter spacing on drip tape was 30 cm. Total water volume per cycle was 41,316 liters/ha, based on application to only the 60-cm-wide beds. Treatments not scheduled to receive nematicide at a particular timing received irrigation but no nematicide. Soil temperatures at 10 cm below the soil surface were 30.6, 30.0, and 31.1°C at fumigation, transplanting, and post-plant chemigation, respectively.

The main experiment was conducted in 2019 and repeated in 2020. Treatments were 1,3-D and fluopyram, alone or in combination, as well as oxamyl alone, as described in Table 1. Oxamyl and fluopyram rates were based on the maximum labelled rate, whereas 1,3-D rate was based on local standard practices. The 1,3-D fumigation was conducted as described for the 2018 trial, except that fumigation was conducted 44 and 43 days before planting in 2019 and 2020, respectively. Fluopyram and oxamyl treatments were chemigated as described for fluopyram in the 2018 trial at the timings specified in Table 1. Oxamyl was applied in the form of Vydate L (Corteva Agrisciences, Wilmington, DE). Soil temperatures (10‒cm depth) in 2019 were 31.8, 29.9, and 32.1°C at fumigation, transplanting, and post-plant chemigation, respectively. Soil temperatures in 2020 were 32.0, 30.3, and 27.3°C, at fumigation, transplanting, and post-plant chemigation, respectively.

Timing of important trial management and data collection events are summarized in Table 2. In each trial, a plot consisted of 1 plasticulture tomato bed (60–cm wide) that was 12.2–m long with 1.83–m row spacing (center to center) and 3.05–m unplanted buffer lengthwise between plots. Approximately 10 days before planting, beds were shaped mechanically by pulling soil from a 1-m-wide band and formed with reflective low density polyethylene plastic mulch. Lengthwise and crosswise unbedded areas between bedded plots ensured fumigant did not move between beds. Trials were transplanted with root-knot nematode susceptible tomato (“Grand Marshall” in 2018 and “BHN 602” in 2019 and 2020) on August 23, 2018, September 5, 2019, and September 5, 2020. Plant spacing was 45 cm. Weed, fertility, disease, and insect management was uniform across the trial and done in accordance with local practices. Irrigation was regulated to maintain soil moisture at 8–12% volumetric water content using a time-domain reflectometry (TDR) soil moisture probe. Irrigation was applied daily, if needed, for 30 min.

Tomatoes were harvested by hand in each trial. In 2018, all large-size tomatoes (greater than 6.99–cm diameter) were picked on November 9 (78 DAP) and November 20 (89 DAP). On November 29, 2018 (98 DAP) all tomatoes were picked, regardless of size, and the trial was terminated. Total yield and yield for each individual date were calculated for the 2018 trial.

For the 2019 and 2020 trials, tomatoes were harvested only once, due to slightly later planting, frost timing, and labor availability. Tomatoes were harvested on December 4, 2019 (90 DAP) and December 2, 2020 (88 DAP). In 2019 and 2020, tomatoes were mechanically sorted by size grade before weighing using a Kerian Speed Sizer (Kerian, Grafton, ND). Size classes were cull, small (6 × 7), medium (6 × 6), and large (5 × 6), representing diameters (cm) of < 5.7, 5.7 to 6.3, 6.4 to 7.0, and > 7.0, respectively. Size classes were based on the Florida Marketing Order (USDA-AMS, 2005). In addition to yield by size grade, marketable yield (small, medium, or large) and total yield (cull plus marketable) was calculated. For the 2019 and 2020 trials, basic economic data was calculated. Total crop value for each plot was determined based on reported price by size grade for the Central and South Florida shipping point at the time of harvest each year (USDA-AMS, 2019; USDA-AMS, 2020). In 2019, prices (in USD) were 11.95, 13.95, and $17.95 per 11.4 kg carton for small, medium, and large size grades, respectively. In 2020, prices were 17.95, 19.95, and $21.95 per 11.4 kg carton for small, medium, and large size grades, respectively. In addition, net income was calculated as crop value minus nematicide product cost. This did not consider labor, fuel, equipment, or other additional costs of nematicide application. Nematicide product costs were determined based on an informal survey of local agrochemical suppliers at the time of publication and are provided as an estimate only. Nematicide product cost (USD) estimates per hectare were $780 for 1,3-D alone; $851 for 1,3-D plus fluopyram; $72 for fluopyram alone; and $61 for oxamyl alone.

Before each trial, a composition soil sample was collected from the trial site just before fumigation to verify M. incognita infestation. Using an Oakfield tube, 15 cores to 25–cm depth were collected randomly across the trial site and homogenized. Nematodes were extracted using the sucrose-centrifugation method (Jenkins, 1964), and quantified morphologically using a Primovert microscope (Carl Zeiss AG, Oberkochen, Germany) at 100 times magnification. There were 30, 45, and 14 M. incognita J2/100–cm³ soil before planting in 2018, 2019, and 2020, respectively.

For the 2019 and 2020 trials, at harvest, before tomato vines were terminated, soil samples were collected to determine M. incognita and free-living nematode abundances. From each plot, 12 soil cores to 25–cm depth were collected at the base of plants. Soil was mixed by hand, and nematodes were extracted as previously described. Both M. incognita J2 and total free-living nematodes abundances were quantified morphologically by microscope as previously described. Nematode soil abundances at harvest were not determine for the 2018 trial. For all three trials, root surface galling was quantified just after harvest. After harvesting, root surface galling was rated from 0 to 100% for 10 plants per plot (Barker et al., 1986).

Each trial was analyzed separately. Data were subject to one-way ANOVA. Before completing ANOVA, response variables were transformed, if needed, to meet assumptions of homogeneity of variance using Levene’s test (Levene, 1960) and normality of residuals based on graphing (Cook and Weisburg, 1999). Specifically, total yield in 2018 and galling in 2020 were square-root transformed. Other variables were not transformed. For variables with significant (α = 0.05) treatment effects in ANOVA, means were separated by Fisher’s LSD (α = 0.05). Analyses were conducted in R statistical software (version 3.4.4, The R Foundation for Statistical Computing, Vienna, Austria).

In the preliminary trial conducted in 2018, root galling at harvest was significantly lower with any nematicide treatment compared with untreated control (ranging from 33 to 61% reductions), but there were no significant differences among nematicide chemistries or combinations (Figure 1A). Similarly, total yield was greater for any nematicide treatment than untreated control (19–32% increases) with no significant differences among treatments with nematicide (Figure 1E). This was driven by yield at the 2nd picking, which had significant differences (Figure 1C), as there were no significant differences at the first (Figure 1B) or third picking (Figure 1D).

Figure 1:

In the 2019 and 2020 trials, nematicides varied in their management of M. incognita. In 2019, treatments with 1,3-D alone or in combination with fluopyram reduced root galling compared with untreated control, fluopyram alone, or oxamyl (Figure 2). Galling was reduced 59 and 72% by 1,3-D and 1,3-D with fluopyram, respectively, relative to untreated in 2019. Soil population densities of M. incognita followed a similar numeric trend to galling in 2019, but there were no significant treatment effects (Figure 2). In 2020, oxamyl or 1,3-D with or without fluopyram reduced galling compared with fluopyram alone or untreated control (Figure 2). In 2020, galling reductions relative to untreated control were 88, 94, and 97% for oxamyl; 1,3-D; and 1,3-D plus fluopyram, respectively. Trends in 2020 M. incognita soil abundances were similar, with oxamyl or treatments with 1,3-D reducing soil abundances 95–98% relative to untreated, except that fluopyram alone was intermediate to untreated control and oxamyl (Figure 2). In both 2019 and 2020, nematicides had negative impacts on non-target, free-living nematodes, although impacts of specific chemistries varied somewhat by year. In 2019, any nematicide treatment reduced free-living nematode soil abundances 51–63% relative to untreated control, except that oxamyl alone was intermediate between untreated and the other nematicides (Figure 3). In 2020, oxamyl, 1,3-D, or 1,3-D with fluopyram reduced free-living nematode abundances 48–60% relative to untreated or fluopyram alone.

Figure 2:

Figure 3:

Nematicides affected crop performance in 2019, but not 2020. In 2019, marketable yield (Figure 4), small size category yield, total yield (Table 3), and crop value (Figure 4) were greater for 1,3-D alone than untreated or fluopyram alone. For 1,3-D alone, marketable yield, crop value, and small size yield increases were 78, 78, and 65%, respectively. However, net income in 2019 was not affected by nematicide treatments (Figure 4). In 2020, marketable (Figure 4), total, small, medium, and large yields (Table 3) were not significantly affected by nematicide treatments. Similarly, neither crop value nor net income was affected by nematicide treatments in 2020 (Figure 4).

Figure 4: