Hydrogen cyanamide (cyanamide) has been used as a dormancy-breaking and bloom-hastening agent of deciduous fruit trees for many years (Carreno et al., 1999; Diaz et al., 1987; Dozier et al., 1990; Subhadrabandhu, 1995). Induction of uniform and earlier budbreak with cyanamide is reported to improve management and production of several deciduous crops in several tropical and subtropical areas worldwide (Aksoy et al., 1995; Buitrago et al., 1992; Carreno et al., 1999; Dozier et al., 1990; George and Nissen, 1993; Inglese et al., 1998; Jackson and Bepete, 1995; Lloyd and Firth, 1993; Or et al., 1999; Pontikis, 1989; Schuck and Petri, 1995; Snir and Erez, 1988; Tanino et al., 1989; Wood, 1993). In some regions, cyanamide use is a component of routine commercial production for several crops [e.g., apple (Malus × domestica), blueberry (Vaccinium corymbosum and hybrids), grape (Vitis vinifera), kiwifruit (Actinidia deliciosa), and peach (Prunus persica)].
Individual citrus trees in south Florida sometimes bloom for more than 1 month (E. Stover, unpublished data). Even greater bloom duration occurs within most orchard blocks because of variation in bloom timing between trees. Such prolonged bloom contributes to variable fruit maturity and increases severity of floral fungal diseases. PFD is a serious floral fungal disease caused by C. acutatum. This pathogen is stimulated to grow and produce spores by flower exudates; therefore, off-season or prolonged bloom period provides greater opportunity for inoculum development and makes disease control more difficult (Dewdney and Graham, 2016). PFD results in young fruit abscission and sometimes causes severe yield losses (Peres et al., 2002). Epidemic huanglongbing [HLB (associated with the bacterium Candidatus Liberibacter asiaticus)] in Florida causes the trees to be under chronic stress and results in multiple bloom periods and off-season bloom throughout the year (Dewdney and Graham, 2016), which exacerbates severity of PFD. Ability to shorten bloom duration and hasten bloom appears to offer several advantages to Florida citrus producers.
Cyanamide is primarily used on dormant deciduous species, and considerable leaf drop can result in citrus even when cyanamide drifts from adjacent vineyards (Ali and Lovatt, 2001). There is one report that cyanamide advances budbreak in mango [Mangifera indica (Notodimedjo, 1995)], which like citrus, is an evergreen subtropical fruit species. The objectives of this study were to assess phytotoxicity at a range of cyanamide concentrations and determine the potential benefit of using cyanamide to hasten flowering and reduce bloom duration of citrus in south Florida. This work was discontinued due to a change in program direction, but may now have current relevance due to problems associated with HLB and PFD. We find no published data on cyanamide in citrus and therefore submit this information as preliminary data.
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