Epidemiologia da ferrugem e da cercosporiose em cafeeiro irrigado e fertirrigado

Abstract

lrrigation and fertirrigation are practices widely utilized for ex:panding the crop into promising regions limited by low rainfalls or badly distributed raios, aiming to warrant good yields. However, little is known about their influence on crop, enviromnent and pathogens. The order of the present work was carried out to evaJuate the effect of irrigation and fertirrigation under a dripping system in the incidence and severity of rust and brown eye spot, wich is the diseases causing yield fall, and correlate with leafing, both yield and c1imatic conditions of the place. The experiment was carried out in an experimental area of the Agricultural Engineering department of the Universidade Federal de Lavras-MG, utilizing the cultivar Acaiá Cerrado MG 1474 ofthree years in a 0.6 x 3.0 m spacing. The experimental design accomplished in randomized blocks consisted of five plots which were given irrigation depths of O, 40, 60, 80 and 100% of the evaporation of the Class A pan (ECA), three subplots of nitrogen and potassium fertilization in 3, 6 and 9 splits, and four replicates. The plots consisted of 30 plants, allocated into three rows (subplots) of 10 plants each, from which only eight were considered useful. The evaJuations of incidence and severity of rust and brown eye spot on the leaves were accomplished in 14 days intervaIs through the symptoms observed on 8 leaves per plant, randomly obtained on the medium third of the plants between the third and fourth pair of leaves on the branch. The incidence and severity of brown eye spot on the fruit was evaJuated on the basis of the symptoms observed on 140 fruits ofthe subplot and 420 fruits ofthe plot, obtained when the first depth to reach the rnaturation stage was harvested. The leafing of the plants was still evaJuated, by establishing scores of 1 to 5 according to the percentage ofleafing, 1 being (O to 20%),2 (21 to 40%),3 (41 to 60%), 4 (61 to 80%) and 5 (81 to 100% ofleafing). The results obtained from the incidence and severity evaJuations of the leaves and leafing were transfonned into area below the progress curve of disease and leafing, respectively, before being assessed statisticaJly. Climatic data of rainfall (mm), maximum, medium and minimum temperature ('C) and air relative humidity (%) were obtained daily from Universidade Federal de Lavras campus weather station for correlation with the diseases evaJuated. On the basis of the results, it was found that the incidence of rust was not influenced by the different irrigation depths and fertilization splits. Nevertheless, there was a greater severity of rust when submitted to higher irrigation depths. Incidence and severity were correlated negatively with the climatic variables in alI the treatments of depths. As to brown eye spot, both incidence and severity was the greater both on the leaves and on the fruits the lower the irrigation depth applied to the crop. The correlation between the incidence of brown eye spot in the irrigation treatments (40, 60, 80 and 100% ECA) and ali the climatic variables with the exception of relative moisture, was significantIy negative. The diseases rust and brown eye spot occurred with grater intensity during the months of June/July and May/Jun, respectively. There was still a positive correlation on plants with a greater leafing submitted to higher irrigation depths. The fertilization splits singly did not influence the analyzed variables but in interacting with the maximum irrigation depth (100% ECA), the presented increased yield of the crop and severity of brown eye spot on the leaves when the fertilization was splitted into three times. Under 0% depth ECA, the highest incidence of brown eye spot on the fruits occurred when the fertilization was accomplished in 3 or 9 splits.