Better spray coverage can improve efficacy of abscission sprays for mechanically harvested oranges

Jacqueline K. Burns, Luis Pozo, Kelly Morgan, Fritz Roka


The selective fruit abscission compound 5-chloro-3methyl-4-nitro-1H-pyrazole (CMNP) improves mature fruit removal of mechanically harvested orange trees in Florida. Uniform fruit removal depends on peel contact by CMNP sprays. When conventional radially discharging air-blast (AB) sprayers are used, fruit removal is variable, especially in tall dense canopies. Fruit detachment force (FDF) and fruit removal were measured when CMNP was applied with an AB or a multi-head air-blast 'GreenTech' (GT) sprayer. CMNP (200 ppm [200 mg L-1]) was applied at 1873 and 2810 L ha-1 (200 and 300 gal acre-1) with the AB or GT sprayers to 'Hamlin' orange [Citrus sinensis (L.) Osb.] in Immokalee, Fla. A second trial was conducted in 'Valencia' orange in Immokalee that included a 1405 L ha-1 (100 gal acre-1) application. Four days after treatment, FDF at heights of 1, 2, and 4 m (approx. 3', 6', and 12') at inside and outside canopy positions were determined. Fruit from GT-sprayed trees had lower and more uniform FDF at all canopy positions. In contrast, fruit from AB-sprayed trees had greater variability in FDF, especially at the top and inside the canopy. Fruit were mechanically harvested using a trunk shake-and-catch system. Mature fruit removal was greater and less variable in GT-sprayed than AB-sprayed trees and required less spray volume. The results demonstrate that uniform CMNP coverage can minimize variation in its efficacy and improve mature fruit removal of trees harvested with a trunk shaker.


abscission agent; fruit detachment force; mature fruit removal; fruit recovery; sprayer

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