Effects of girdling, chemicals and plant growth regulators on production and fruit quality of 'Hong Huay' lychee

Effect of girdling, chemicals and plant growth regulators for improving production and fruit quality in 'Hong Huay' lychee were conducted in Chiang Mai, Chiang Rai and Pha Yao Provinces, Thailand during 2016 and 2018. The experiments consisted of: 1) application of ring cincturing, foliar fertilizers and plant growth regulators for flower induction; 2) application of spiral cincturing, chemicals and plant growth regulators to increase fruit set; and 3) application of spiral cincturing and plant growth regulators to increase fruit size. There were six orchard × year combinations out of 15 tested had significantly different in average flowering percentages. Soil application of 300 g tree^‑1 paclobutrazol (10% WP) followed with 200 g tree^‑1 potassium chlorate (99% WP) had higher average flowering percentages than the control treatment but were significantly different in only three orchard×year combinations. Ring cincturing of limb followed with spraying with 10 g L^‑1 0-52-34 (1%) fertilizer mixed with 800 mg L^‑1 ethephon (48%) had higher average flowering percentages than control treatment but were significantly different at only at two orchard×year combinations. Spiral cincturing of blooming branches tended to have the highest average fruit set which was higher than the control treatment but significantly different only at three orchard × year combinations out of seven tested. Spraying with 400 mg L^‑1 uniconazole also-increased average fruit set more than the control treatment but was significantly different only at one orchard. Spraying with 5 mg L^‑1 brassinolide tended to increase average fruit weight more than that in the control treatment but the effect was significant only at four orchard×year combinations out of eight tested. Further testing is required before recommendations can be made to lychee growers.