Quantification of monocyclic parameters and chemical control of peach rust

A ausência de um controle eficiente da ferrugem do pessegueiro é a causa do aumento da importância dessa doença em regiões subtropicais. Visando um conhecimento das interações patógeno-hospedeiro-ambiente foi avaliado o efeito da temperatura na germinação de uredósporos do fungo e nos parâmetros monocíclicos da doença. O estudo das temperaturas de 8, 18, 23, 28 e 36"graus"C indicou a faixa de 10 a 22"graus"C como sendo a ótima para a germinação. A temperatura de 18"graus"C proporcionou uma maior frequência de infecção e um maior período latente do que a temperatura de 23"graus"C a eficiência de onze defensivos agrícolas foi avaliada através de testes "in vivo" "in vitro" foram determinadas a porcentagem de germinação de uredósporos em meio ágar-água com defensivo nas concentrações de 1, 10 e 100 PPM e a ED50. In vivo a eficiência dos produtos foi avaliada em plantas adultas dos cultivares flor da prince e auroraII. Os experimentos consistiram de quatro aplicações dos produtos nas dosagens comerciais recomendadas. A intervalos quinzenais os produtos Mancozeb Captan e Tebuconazole foram os mais eficientes tanto in vitro como in vivo. O efeito protetor curativo e erradificante do inseticida Cartap foi avaliado em mudas do cultivar tropical. O tratamento protetor apresentou eficiência máxima, na forma curativa houve redução da doençaThe lack of an efficient control of the peach rust caused by Tranzschelia discolor (Fuckel) Tranzschel & Litivinov is the main cause of increase in importance of this disease in subtropical regions. The establishment of an adequate disease management system is possible only after the knowledge of the pathogen - host - environment interactions. In order to get a better understanding of these relationships the effect of temperature on the germination of uredospores of T. discolor and the monocyclic parameters of the disease was evaluated. The optimum estimated temperature range for uredospore germination was 10 to 22°C in the study where the temperatures employed were 8, 18, 23, 28 and 36°C. The monocyclic parameters (infection frequency and latent period) were quantified on growth chamber condition on peach plants of the cultivar Flor da Prince, at the temperatures of 18 and 23°C. The temperature of 18°C gave a higher infection frequency and a larger latent period then the temperature of 23°C. The efficiency of eleven chemical products on the control of the disease was evaluated though in vitro and in vivo tests. The percentage of uredospore germination in water - agar at the concentrations of 1, 10 and 100 ppm of the chemicals and the ED50 were determined. The efficiency of the products to control of peach rust, at field condition, was also evaluated in adult plants of cultivars Flor da Prince and Aurora II. The trials consisted of four applications, at the commercial dosages recommended, in a 15 days interval, the evaluation being made through the disease severity and the defoliation degree. Mancozeb, captan and tebuconazole were the most efficient, both in vitro and in vivo conditions. Bitertanol and propiconazole did not differ from control. The protective, curative and erradicant effects of the insecticide cartap was evaluated in peach plants of the Tropical cultivar, under the temperature of 21 ± 4°C. The protective treatment showed maximum efficiency, with no pustule formation on the leaves. In the curative form, cartap reduced significantly the infection frequency and increased the latent period in relation to the control. The erradicant treatment gave partial control of the disease, with a great number of active pustules being observed some days after the product application