Relationship among chemical defoliation, vegetative reproductive parameters and entomosporium leaf spot (Entomosporium mespili) of pear in southern Brazil

Leaf fall induced by chemical sprays can be used to facilitate farm labor management. The objective of this study was to evaluate the effect of chemical defoliants AVG, ethephon and calcium chloride on the physiology-reproductive parameters and entomosporium leaf spot (ELS) (Entomosporium mespili) epidemiology of three European pear cultivars, during the 2011/12, 2012/13 and 2013/14 growing seasons, in southern Brazil. The experiments were carried out in a commercial pear orchard in Vacaria Municipality, Rio Grande do Sul State, southern Brazil. The European pear cultivars ‘Packham’s Triumph’, ‘Abate Fetel’ and ‘Williams’ grafted on quince Adams were sprayed with AVG – aminoethoxyvinylglycine; ethephon and calcium chloride and compared to control – without application. The treatments were sprayed on average 45 days after harvest on 19/03/2012, 14/03/2013 and 18/03/2014. The vegetative-reproductive parameters analyzed were percentage of leaf fall, bud quality, budding return and production. The entomosporium leaf spot severity data were integrated over time, and converted into the area under the disease progress curve. The experiments followed a completely randomized block design with four replicates, using three plants per experimental plots. The more effective compound was ethephon with approximately 100% of defoliation after 21 days of application. The AVG and calcium chloride showed a similar effect to the control. Calcium chloride caused budburst in all evaluated cultivars. No significant differences were found in the bud quality, budding return and production. There were no undesirable effects on the physiological parameters when the leaf fall was induced by chemical defoliants. Ethephon showed potential performance to induce leaf fall without any undesirable effect on the physiology-reproductive parameters in all pear cultivars during growing season considered. However, further experiments must be carried out in different times to better evaluate the effects of chemical defoliants.