TIME OF ERGER APPLICATION FOR BUDBREAK INDUCTION IN APPLE TREES

Abstract

More than 50% of the Southern Brazilian apple production is located in areas where chilling varies from 800 to 1.200 cold units by the North Carolina model, or from 400 to 600 hours of temperature below 7.2°C. This low chilling results in budbreak and blooming delay, which requires artificial budbreak induction. Erger, an inorganic nitrogen compound, combined with calcium nitrate, has a similar effect to that of hydrogen cyanamid, with the advantage of being less dangerous to the environment. Budbreaking products are influenced by environmental factors, but mainly by the temperature at the time of application or during the following days, which should be at least 20°C. The aim of this experiment was to evaluate the effects of time of Erger 5% + Calcium Nitrate 5% application on budbreak induction of 'Imperial Gala' and 'Suprema' apple trees. The experiment was carried out in Cacador, Brazil (lat. 26°46'31), in an RCB design with five treatments and six single tree replications. The treatments were a check and four fortnightly Erger applications. Phenology, axillary and terminal budbreak, fruit set, fruits per cluster and mean fruit weight were evaluated. In comparison with the check treatment, Erger 5% + calcium nitrate 5% anticipated up to 28 days the full bloom of 'Imperial Gala' when applied on August 15, but only up to 13 days if applied on September 15. The effect on 'Suprema' was at a lesser extent than on 'Imperial Gala'. The axillary's budburst of 'Imperial Gala' significantly increased when the plants were treated on August 1, differing from the check up to 60 days after application. The axillary's budbreak on 'Suprema' was greater than on the check trees except for the application on August 15 because of the low temperature that persisted also during the following days. The low temperature affected the response in both cultivars. Fruit set of 'Imperial Gala' was not affected by the time of treatment application, but it was reduced in 'Suprema' when applied on August 1. There was a tendency of mean fruit weight increase on treated plants, probably related to a longer bloom-ripening period.