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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #328251
Title: Hydrogen cyanamide on citrus: Phytotoxicity, influences on flush in potted and field trees and effects on bloom and cropload in the field

Author
item Stover, Eddie
item LIN, YOUJIAN - University Of Florida
item YANG, XIAOE - University Of Florida

Submitted to: Florida State Horticultural Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2016
Publication Date: 6/13/2016
Citation: Stover, E.W., Lin, Y., Yang, X. 2016. Hydrogen cyanamide on citrus: Phytotoxicity, influences on flush in potted and field trees and effects on bloom and cropload in the field[abstract]. Annual meeting of the 129th Florida State Horticultural Society. June 12-14, 2016, Stuart, Florida

Interpretive Summary:

Technical Abstract: Bloom in individual citrus trees typically continues for more than a month in south Florida. Prolonged bloom increases susceptibility to postbloom fruit drop disease (caused by Colletotrichum acutatum) and contributes to variable fruit maturity at harvest. Hydrogen cyanamide (HCN) is used to accelerate and compress bloom in various deciduous fruits, and this study investigated its use in citrus. HCN (in the product Dormex) was applied at a concentration range from 0.125 percent to 1.0 percent a.i., to potted trees of six citrus genotypes (Citrus macrophylla, Duncan grapefruit, Smooth Flat Seville, sour orange, Swingle citrumelo, Sun Chu Sha, and Duncan grapefruit) in December while trees were quiescent. Phytotoxicity increased with HCN rate, with some damage at 0.125 percent HCN on most genotypes, and large variation among genotypes. All HCN rates accelerated flushing. Airblast application of HCN (0, 0.025 percent, 0.05 percent, and 0.10 percent) was made to mature trees of Valencia and Navel orange in Ft. Pierce, Florida, on January 27. On February 15 and February 28 additional trees received HCN at 0.05 percent. There was considerable defoliation which increased linearly with HCN rate. Flushing and flowering were unaffected by HCN compared to controls except that February. HCN appeared to increase flowers per tree in Valencia and 0.1 percent HCN on January 27 reduced Navel flowering. HCN application to Valencia on February 28, after initial flowering, but 16 days before peak bloom, significantly reduced fruit per tree, but there were no other effects on cropping. HCN did not accelerate bloom with applications late January through February.