Effects of label and sub-label rates of dazomet and metham-sodium on survival of Calonectria microsclerotia

Calonectria species have been reported as devastating pathogens mostly on horticultural and forest crops worldwide. Since these pathogens represent a serious threat for the nursery production in the Mediterranean basin, the aim of this study was to investigate the effects of label and sub-label rates of dazomet (Basamid) and metham-sodium (Divapan) for eradicating C. ilicicola, C. mexicana, C. morganii, C. pauciramosa, C. polizzii, C. pseudomexicana, and C. tunisiana inocula from substrate. Primary inoculum of Calonectria spp. consists of microsclerotia differentiated on senescing plant tissues and control measures to reduce potential inoculum in infected substrate is needed to reduce the following infections in nurseries. The effects of fumigants were investigated in microcosm and open field using artificially infested soil. Two experiments were carried out in plastic containers and field in a commercial nursery located in Catania province (Sicily, Italy). Basamid was used at 100, 200, and 250 g/m3 while Divapan rates were 400, 700, and 1000 L/ha. The fumigants were applied under virtually impermeable film (VIF). The containers and plots were artificially infested with microsclerotia of the seven Calonectria species produced on a carnation leaf agar medium (CLA). Carnation leaf segments colonized by pathogen microsclerotia were placed in nylon mesh bags and buried in the substrate. All treatments were replicated three times, in a completely randomized design. The survival of each Calonectria isolate was estimated in each plot after 21 days on potato dextrose agar (PDA) amended with streptomycin sulphate. The microsclerotia infection ability was tested on red clover (Trifolium pratense). With the exception of the lower rate of metham-sodium, all treatments killed Calonectria microsclerotia. This paper demonstrates that the use of low rates of dazomet and metham-sodium is effective for Calonectria microsclerotia suppression in nurseries. However, some little differences in levels of eradication could be attributable to Calonectria species.