New conventional nematicides help manage root-knot nematodes in carrot production

Root-knot nematodes are a pervasive problem in vegetable production in the Southeast. They are especially problematic in root crops like carrots, because these nematodes disfigure the roots, reducing the quality of the marketed crop part (Figure 1). When root-knot nematodes are present, protecting the crop from damage is important and nematicide application is one of the main tools for this. In recent years, new conventional and biological nematicides have become available in vegetable production. The purpose of this article is to summarize recent University of Florida small plot trials testing the efficacy of nematicides in carrot production.

<strong>Figure 1.</strong> Carrot roots in a plot not treated with nematicide in a Live Oak field trial. Roots exhibit damage from root-knot nematode, including forking or splitting of tap roots and small galls or knobs on lateral roots and root hairs. — **Figure 1.** Carrot roots in a plot not treated with nematicide in a Live Oak field trial. Roots exhibit damage from root-knot nematode, including forking or splitting of tap roots and small galls or knobs on lateral roots and root hairs.

Methods

Replicated small plot field trials were conducted at UF research stations near Live Oak and Citra, FL from September 2025 to February 2026. There was severe infestation of root-knot nematodes in both fields. Various conventional and biological nematicides (some labelled and some not yet labelled for carrots) were compared to untreated or Telone II fumigation (Table 1). Various crop growth and nematode population/damage assessments were made during the season and yield was assessed at the end of the season. For labelled products, return on investment was calculated based on estimated crop value and product costs.

Findings:

1. Severe root-knot nematode infestation can reduce carrot stand and early growth

Early in the season, plant stand and vigor was clearly reduced in certain treatments, especially at the Live Oak site (Figures 2 and 3). Reduced stand was due to root-knot nematode damage as the untreated had poor stand, which rules out phytotoxic effects from nematicides. Additionally, growth was reduced in treatments with poor nematode control as shown later. These results were an early indicator of nematicide performance and reinforced the threat from root-knot nematode.

Figure 2. At the Live Oak site, carrot stand and vigor varied by plot at 45 days after planting. The left plot (2 stakes) is the untreated control and the right plot is Salibro nematicide. — **Figure 2.** At the Live Oak site, carrot stand and vigor varied by plot at 45 days after planting. The left plot (2 stakes) is the untreated control and the right plot is Salibro nematicide.

Figure 3. Plant canopy vigor at 8 weeks after planting as affected by nematicide treatments in Live Oak and Citra small plot field trials. Vigor is a visual rating on 0-100 scale with 100 best. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide. — **Figure 3.** Plant canopy vigor at 8 weeks after planting as affected by nematicide treatments in Live Oak and Citra small plot field trials. Vigor is a visual rating on 0-100 scale with 100 best. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide.

2. Fumigation was still the most effective nematicide

Fumigation using Telone II consistently performed in the top group for managing root-knot nematode populations and improving yield, with selected data shown in Figures 4, 5, and 6. Midseason root-knot nematode counts from carrot roots (Figure 4) are a good indicator of nematode infection and help show if growth and yield effects are due to nematodes or other factors. Fumigation reduced root-knot nematode infection to very low levels at both sites (Figure 4). Correspondingly, fumigation produced the best yield and return on investment at Citra and was in the top grouping at Live Oak.

Figure 4. Root-knot nematode egg abundances from roots at 8 weeks after planting as affected by nematicide treatments in Live Oak and Citra small plot field trials. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide. — **Figure 4.** Root-knot nematode egg abundances from roots at 8 weeks after planting as affected by nematicide treatments in Live Oak and Citra small plot field trials. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide.

3. Conventional nematicides had efficacy, sometimes as good as fumigation

Both Salibro and NIMITZ were as good as fumigation at managing root-knot nematode infection at midseason (Figure 4). At Live Oak, these products had marketable yield and return on investment that was very similar to Telone II, while at Citra all conventional nematicides performed worse than Telone II, but were better than untreated (Figures 5 and 6). Velum and the experimental nematicide were less consistent than Salibro and NIMITZ, but showed some efficacy. The presence of sting nematode at the Citra site may have been one factor in the poorer performance of liquid nematicides there as this nematode is known to be difficult to manage from other trials. Especially considering the severe nematode pressure in this trial, these results suggest that liquid conventional nematicides can be useful options for root-knot nematode management. They may not perform as well as fumigation, but there is a place for them in nematode management strategies.

Figure 5. Marketable yield in Live Oak and Citra small plot field trials as affected by nematicide treatments. Marketable yield (USDA #1 and #2) was calculated from total yield and proportion marketable from a 5 gallon subsample graded from each plot. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide — **Figure 5.** Marketable yield in Live Oak and Citra small plot field trials as affected by nematicide treatments. Marketable yield (USDA #1 and #2) was calculated from total yield and proportion marketable from a 5 gallon subsample graded from each plot. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide

4. Biological nematicides were not effective in this study

Neither of the biological nematicides tested in this carrot study improved management of root-knot nematode infection or carrot production (Figures 4-6). In carrot production with severe pressure from root-knot nematode, the biological nematicides tested were not effective options. Under other conditions or with other products, biological nematicides may be more effective, although that is outside the scope of this study. In particular, the severe nematode pressure in this study may have been too much for the biologicals to manage.

Figure 6. Marginal income relative to the mean for untreated control in Live Oak and Citra small plot field trials. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide. — **Figure 6.** Marginal income relative to the mean for untreated control in Live Oak and Citra small plot field trials. Means with different letters are significantly different (Fisher’s protected LSD, P<0.05). “EXP” is an “experimental” nematicide.

Conclusion

Effective options are available for root-knot nematode management in carrot, even in situations where pressure is extreme. When root-knot nematode pressure levels warrant application, growers should select an effective nematicide that fits their operation.

Acknowledgements: Funding from the California Fresh Carrot Advisory Board. Work by Sabina Budhathoki, A. Korede Oyetunde, Esther Momoh, Bob Hochmuth, NFREC-SV farm staff, and PSEU farm staff made this study possible.