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ARS Home » Research » Publications at this Location » Publication #331495
Title: Hydrogen cyanamide on citrus: preliminary data on phytotoxicity and influence on flush in potted and field trees

Author
item Stover, Eddie
item LIN, YOUJIIAN - University Of Florida
item YANG, XIAOE - University Of Florida
item VASHISTH, TRIPTI - University Of Florida

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2016
Publication Date: 12/3/2016
Citation: Stover, E.W., Lin, Y., Yang, X., Vashisth, T. 2016. Hydrogen cyanamide on citrus: preliminary data on phytotoxicity and influence on flush in potted and field trees. HortTechnology. 26:839-845.

Interpretive Summary: In Florida citrus, prolonged bloom contributes to variable fruit maturity at harvest and increases severity of a disease which affects flowers. Hydrogen cyanamide (HCN) has been effective in accelerating bloom in other fruit trees, and its potential use in citrus was investigated in this study. In small potted trees treated in December, tree damage increased with HCN rate, with some damage at 0.125% HCN on most genotypes, and large variation among genotypes. All HCN rates accelerated flushing. Mature sweet orange trees were treated on 27 January 2000- 28 February. Some defoliation was observed from HCN. In these trials HCN was not an effective agent for accelerating bloom. Further work is needed to determine whether December applications of HCN may be more effective in concentrating subsequent flush and bloom.

Technical Abstract: Bloom in individual citrus trees typically continues for more than a month in south Florida, with even greater bloom duration within most orchard blocks because of variation in bloom timing between trees. Prolonged bloom contributes to variable fruit maturity as harvest approaches and increases severity of postbloom fruit drop disease (caused by Colletotrichum acutatum). Hydrogen cyanamide (HCN) has been effective in accelerating bloom in various deciduous fruits, and its potential use in citrus was investigated in this study. HCN was applied at a range of concentrations, from 0.125% to 1.0% a.i., to potted trees of six citrus genotypes reflecting much of the diversity in commercial citrus (Citrus macrophylla, ‘Duncan’ grapefruit, ‘Smooth Flat Seville’, sour orange, ‘Swingle’ citrumelo, and ‘Sun Chu Sha’ mandarin) in December while trees were quiescent. Phytotoxicity increased with HCN rate, with some damage at 0.125% HCN on most genotypes, and large variation among genotypes. All HCN rates accelerated flushing. Airblast application of HCN (0, 0.025%, 0.05%, and 0.10%) was made to mature trees of ‘Valencia’ and ‘Navel’ orange in Ft. Pierce, Florida, on 27 January 2000. On 15 February and 28 February additional trees received HCN at 0.05%. There was considerable defoliation which increased linearly with HCN rate. Flushing and flowering were unaffected by HCN compared to controls except in February where HCN applied at 0.05% increased flowers per tree in ‘Valencia’, and in contrast, 0.1% HCN on 27 January reduced ‘Navel’ flowering. HCN application to ‘Valencia’ on 28 February, after initial flowering but 16 days before peak bloom, significantly reduced fruit per tree but there were no other effects on cropping. In these trials HCN was not an effective agent for accelerating bloom in south Florida citrus with applications late January through February. Further work is needed to determine whether December applications of HCN may be more effective in concentrating subsequent flush and bloom. In addition, it is hypothesized that HCN-enhanced flushing in the fall may provide reduced callose plugging in phloem of huanglongbing (HLB)-affected citrus. This is founded on possible common physiology between metabolism/degradation of callose plugs as plants are forced out of dormancy and the callose plugging of phloem in huanglongbing-affected citrus.