This experiment was carried out during 2018 and 2019 seasons to investigate the effect of spraying marine algae extracts (Ascophyllum nodosum) and some growth regulators (GA3 and NAA) to reduce fruit drop and improve fruit yield and quality of winter guava trees cv. ‘Maamoura' grown in Rasheed area, El Beheira, governorate, Egypt and cultivated at a distance of 4 x 4 m. The irrigation method was flood irrigation from the Nile River. Trees, as uniform as possible in shape and size, were selected and had the same horticultural management including the control. The experiment involved ten foliage spraying treatments as follows: control, sprayed with water, Seaweed extract at (5, 10 and 15 mg/l), GA3 at (1, 2 and 3 mg/l) and NAA at (1, 2 and 3 mg/l).
The obtained results showed that, GA3 at 3mg/l and Seaweed extract at 15 mg/l had the highest positive effect to improve vegetative growth, total chlorophyll (SPAD), the percentages of fruit set, yield, and total soluble solids (TSS). Moreover, it increased N, P and K in the leaves in the two seasons, as compared to the control and the other treatments. In addition, it improved significantly the number of fruits per tree, fruit weight, length and firmness. Reduction in the percentages of total acidity was observed as compared to the control, in the two seasons.