MANAGING DROUGHT STRESS OF ORANGES UNDER SAO PAULO-MINA GERAIS, BRAZIL CONDITIONS TO OPTIMIZE FLOWER BUD INDUCTION AND PRODUCTIVITY

Winter weather in the Sao Paulo-Minas Gerais citrus production area varies considerably year-to-year, but often there is adequate cold induction in the south and excessive drought in the north. A program of monitoring winter temperature and rainfall data for farms from near Conchal, SP to north of Frutal, MG was instituted starting in 2008 and reported here through 2012. Controlled irrigation experiments were also instituted at two locations in the northern third of SP State, one of which was abandoned due to severe greening disease. Cool temperature induction hours (19°C or less) ranged from <200 to more than 1300 h depending on location and year. Based on an ultralow volume irrigation scheme, deficits in cool temperature induction were compensated for by a moderate drought stress management system (MDSM) to achieve adequate flower bud induction without excessive drought stress. In the ultralow volume drip irrigation experiments soil moisture tensiometers indicated that keeping just the surface 20 cm with adequate moisture levels prevented severe drought and required less than 1 mm/day. These treatments kept trees in adequate condition without initiating bud sprouting for up to 120 days until released by full irrigation to allow normal bloom. The moderate stress could be released at any time in order to initiate an earlier bloom as long as water was available for normal irrigation until the rainy season started. Thirty-five to 40 days were required from initiating full irrigation until full bloom. Yields were very satisfactory in four of five years under this program which is now being used on over 10,000 ha.