Management of Chrysanthemum Verticillium Wilt through VIF Soil Mulching Combined with Fumigation at Label and Reduced Rates

Pre-plant soil fumigation for managing soilborne pathogens is practiced worldwide in several intensive ornamental and vegetable production areas. However, global regulations are currently implemented to minimize use of these chemicals. According to these policies, the efficacies of dazomet (DZ, Basamid Granulat^®) applied alone to soil and under virtually impermeable film (VIF) at reduced (247.5 kg ha⁻¹ a.i.) and label (495 kg ha⁻¹ a.i.) rates were assessed in managing natural infections of Verticillium wilt and in reducing yield losses on greenhouse chrysanthemum plantations in two trials carried out in the 2012 and 2013 seasons. The performances of this fumigant at a lower rate combined with VIF application were also compared with standardized metam-sodium (MS, Divapan^®) fumigation applied at 510 L ha⁻¹ a.i. under VIF and application of dazomet at label rate alone to bare soil. Temperatures were monitored at 20-cm depth in plots covered (VIF) throughout the entire fumigation period. Although all fumigation treatments significantly reduced the infection level by <i>V. dahliae</i> on chrysanthemum, the performances differed among them. DZ and MS applied at label rates under VIF showed the most effectiveness in controlling Verticillium wilt of chrysanthemum. However, DZ applied to soil at a low rate under VIF mulching showed good performances, which were always better than application of DZ alone at label rate to bare soil. Moreover, when combining a reduced rate of DZ with VIF mulching, chrysanthemum yield losses were reduced in a similar manner to the label rate application under VIF. Based on these findings, DZ application at a reduced rate could be suggested on a large scale to prevent Verticillium attacks on chrysanthemum cultivated on a protected crop. Future studies should be performed to verify the ability of VIF application in inducing high temperatures in soil and above all in enhancing performances of soil fumigation at low rates performed with other natural and chemical sterilants.