Efficacy of Dimethyl Disulfide (DMDS) in the control of the root-knot nematode Meloidogyne incognita and the cyst nematode Heterodera carotae on carrot in field condition in Italy

Dimethyl disulfide (DMDS), in shank application, was used in two field trials on carrot in Emilia-Romagna and Apulia regions (Italy) against the root-knot nematode Meloidogyne incognita and the cyst nematode Heterodera carotae. The soil was subdivided in plots 30 or 50 × 4.8 m for shank application with machines. Each plot was subdivided in 4 or 5 sub-plots to provide replications for each treatment. In the trial with M. incognita treatments were: i) DMDS at the rate of 250 L/ha, ii) granular oxamyl (60 kg/ha) followed by the commercial product Micosat F WP NE (6 kg/ha) and iii) granular oxamyl (60 kg/ha) followed by Bioact WG including Paecilomyces lilacinus (4 kg/ha). In the trial with H. carotae treatments were: i, ii and iii, DMDS at the rates of 370, 280 and 180 L/ha and iv) 1,3 dichloropropene (140 L/ha). In both trials untreated soil was used as control. DMDS was applied 3 weeks before sowing in a wet soil (70% of the water holding capacity) with a temperature higher than 20°C. The DMDS and 1,3-D treated plots were then covered for 2 weeks with a very impermeable plastic film (VIF). After one week of soil aeration carrot seeds were sown in each plot. At the end of the crop cycle in the experiment with M. incognita, DMDS treatment significantly increased marketable carrot yield (9.7 kg/m2) in comparison to oxamyl followed by either Bioact WG (7.2 kg/m2) or Micosat F WP NE (1.8 kg/m2) and the untreated control (3.9 kg/m2). Also M. incognita soil population density was significantly decreased by DMDS treatment (Pf/Pi=0.2) in comparison to the untreated control (Pf/Pi=14.4) giving the lowest reproduction factor. M. incognita infestation on the roots was assessed according to a scale of 6 classes from 0 to 5. In the experiment in Apulia the significantly highest marketable carrot yield (5.8 kg/m2) was observed in plots treated with 400 L/ha of DMDS in comparison to all other treatments and to the untreated control (0.0 kg/m2). H. carotae soil population density in the untreated control (10.8 eggs and juveniles/g soil) was significantly higher than those observed in the highest DMDS dose (4.5 eggs and juveniles/g soil).