Novica Miletić

Different toxicity of the strobilurin fungicides kresoxim-methyl and trifloxistrobin to Venturia inaequalis isolates from Serbia

Sensitivity of monosporial isolates of V. inaequalis, originated from apple orchards previously exposed (commercial and experimental) and those originated from location where fungicides had never been used (wild type), to strobilurin fungicides kresoxim-methyl and trifloxistrobin was investigated in this study. The experiments were carried out in laboratory using in vitro and in vivo methods. Mycelia growth inhibition on PDA medium with kresoxim-methyl and trifloxistrobin was monitored and sensitivity parameters (EC50 values) were determined using probit analysis. The isolates sensitivity in vivo was tested on apple seedlings using inoculation method. The EC50 values were ranging from 0.066–2.033 and 0.011–0.323 µg mL−1 for kresoxim-methyl and trifloxistrobin, respectively. The wild type of isolates showed a normal susceptibility to kresoxim-methyl and trifloxistrobin, while isolates originated from experimental and commercial orchard where those fungicides had been used extensively, showed significantly lower sensitivity to the both strobilurin fungicides. The isolate that showed the resistance to kresoxim-methyl and trifloxistrobin in vitro test, also showed reduced sensitivity in vivo test and could not been controlled satisfactory by fungicide concentrations that are commercially used, as well as by double higher, after apple seedlings inoculation.

Optimal Timing of Fungicide Applications for the Control of Podosphaera leucotricha, the Causal Agent of Peach Rusty Spot in Serbia

Peach rusty spot has regularly occurred in Serbia in recent years, causing significant economic losses in the production of late maturing cultivars (Summerset, Suncrest, Fayette and O’Henry). Concerns regarding the etiology of this disease have been solved using molecular identification and cross-pathogenicity tests, which have proved that peach rusty spot is caused by Podosphaera leucotricha. The usual recommended strategy for its control, by multiple treatments starting from petal fall phenophase, has not proved satisfactory in agro-ecological conditions in Serbia. After testing the fungicide efficacy, a three-year study was carried out to determine the precise treatment terms and make the control of P. leucotricha more efficient. The investigation was conducted in the conditions of natural infection in a Summerset cultivar orchard at the locality of Bela Crkva, during the period 2006-2008. Nine different variants of both single and mixed treatments were tested, covering six defined peach growth phenophases - from green top, until the phenophase of second fruit falling. In the conditions of high levels of natural infection in the control plots, in all three investigation years the most efficient was the variant in which kresoxim-methyl was applied three times: in green top, pink bud and full bloom phenophases (91.69 - 91.92%), followed by the variant of treatments in the phenophases of rose bud, full bloom and petal fall (86.3-87.87%) and the variant of two treatments, performed in the phenophases of pink bud and full bloom (79.3-83.09%). The other tested variants showed significantly lower efficiency. The results obtained could significantly contribute to better peach fruit production, without losses caused by peach rusty spot which is commercially very important disease in Serbia.