This study was carried out during two successive seasons (2015/016 and 2016/017) on Washington Navel orange trees grown in sandy¿loamy soil under flooding irrigation system with Nile water in a private orchard at Qalub district, El-Qalubia Governorate, Egypt. This experiment studied the effect of spraying trees with diatoms at 0.5, 0.75 and1.00 kg or GA3 at 25 ppm during 25 %, 75 % or twice 25 & 75% of full-bloom on inflorescences types; fruit set %, leaf pigments; leaf minerals content and tree yield efficiency as fruit number & weight and fruit quality. Results showed that spraying of diatoms (0.5kg / 600L) on Navel orange trees at 75 % of full-bloom significantly increased leaf pigments contents.