NAA thinning of 'Murcott': comparison of small plot and commercial harvest data

Ed Stover, Scott Ciliento, Mark Ritenour, Charles Counter


NAA thinning of 'Murcott' was evaluated in four groves near Haines City, Florida using a randomized complete block design with entire rows as experimental units. Groves studied were: 4-, 8-, and 20-yr old 'Murcott' (Citrus reticulata Blanco hybrid) on Cleopatra mandarin (C. reticulata Blanco) rootstock, and 'Murcott' topworked onto 'Ambersweet' [(C. reticulata Blanco×C. paradisi Macf.)×(C. reticulata Blanco)×midseason orange [C. sinensis (L.) Osb.]] on Cleopatra mandarin rootstock in 1999. Treatments were applied 17 May 2001 during early physiological drop, when mean fruitlet diameter was already 0.87-0.95 inches (22-24 mm) with 2-20% of sampled fruitlets less than 20 mm (0.79 inches), and mean cropload was moderately high at 6-8 fruitlets per ft of canopy (64-88). NAA was applied at 250 and 350 ppm plus 0.05% nonionic surfactant, using an airblast sprayer at 60-100 gpa (560-935 L·ha[sup-]). Fruit were harvested January 2002 with small plot data collected (2 trees per row) on 3 of the 4 groves and packinghouse data (all trees combined within each treatment per grove) on two of these groves and one additional grove. NAA increased fruit size in all experiments with little difference between the two rates. Small plot data showed that NAA increased mean fruit weight by 25- 34%, decreased fruit per tree by 24-38%, and decreased fruit yield per tree by 4-24%. Packinghouse data were consistent with small plot results: NAA increased production of 64-100 count fruit by 59-100%, even though no fruit were eliminated because of small size in non-thinned controls. In two of the pack- inghouse assessments, NAA treatments increased packout by 10% of total harvested crop through improved fruit appearance. Crop value was significantly enhanced in only one of three trials that permitted statistical analysis. However, improved return cropping was apparent in all NAA-treated rows the following spring. In addition, the NAA treatment showed better development of young trees, further increasing the potential for improved cumulative two-year returns.


auxin; chemical thinning; citrus reticulata; cropload control; mandarin; naphthaleneacetic acid; tangerine; tangor

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283