compounds that promote hydrolytic digestion of the abscission layer of mature sweet oranges. Of the compounds tested, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) has been shown to be the most effective ( Burns et al., 2005 ; Freeman and Sarooshi, 1976
Robert C. Ebel, Jacqueline K. Burns, and Kelly T. Morgan
Naveen Kumar and Robert C. Ebel
) Hydrogen peroxide (H 2 O 2 ) concentration (n = 15), ( B ) malondialdehyde (MDA)concentration (n = 15), ( C ) specific superoxide dismutase (SOD) activity (n = 15) at various times (d) after a 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) spray treatment
Timothy M. Spann, Luis V. Pozo, Igor Kostenyuk, and Jacqueline K. Burns
, and peel deflection for mechanically harvested (MH) and hand-harvested (HH) ‘Valencia’ sweet oranges treated with and without the abscission agent 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP) in early and late May 2009. CMNP was applied 4 d before
Kuo-Tan Li, Jackie Burns, Luis Pozo, and Jim Syvertsen
To determine the effects of abscission compounds 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) and ethephon on citrus leaf function and water relations, we applied CMNP at 0, 200, 500, 1000, or 2000 ppm, or ethephon at 400 or 800 ppm, to canopies of fruiting potted and field citrus trees during the harvest season. Both compounds induced fruit and leaf drop after 3 days of application, especially at high concentrations. Low concentrations of CMNP (0, 200, or 500 ppm) or either ethephon treatments did not affect leaf photosystem II efficiency, as indicated by leaf chlorophyll fluorescence (Fv/Fm). High concentrations of CMNP (1000 or 2000 ppm) immediately reduced photosystem II efficiency in leaves and fruit peel. However, Fv/Fm of leaves remaining on the trees was gradually restored and close to the level of control after 4 days of treatment. Both compounds had little effect on chlorophyll content, ratio of chlorophyll a to chlorophyll b, leaf water content, and mid-day leaf water potential. The results suggest that CMNP at recommended concentrations (200 to 500 ppm) effectively reduced fruit attachment force with little herbicidal effect on leaves.
S. V. Kossuth, R. H. Biggs, and V. M. Winkler
Uptake and distribution of 14C-labelled 5-Chloro-3-methyl-4-nitro-1H-pyrazole (Release3) was followed in fruit peel of ‘Valencia’ and ‘Hamlin’ orange (Citrus sinensis (L.) Osbeck). Little lateral movement of 300 ppm peel applied Release occurred. Seventy-eight to 94% of the applied 14C-labelled material was found in or on the flavedo, less than 1.5% in the pulp, and 5 to 19% in the albedo tissue. Simulated or true rain removed 70% or more of the 14C-Release during the 0–8 hour period after peel application in the field, but a 24-hour rainless period resulted in recovery of up to 66% of the compound. Under controlled conditions, maximum peel uptake of 14C-Release occurred at 58 to 66% relative humidity (RH) and 25° to 35°C. Increasing RH at lower temperatures only partially increased uptake of Release.
Kuo-Tan Li, Jacqueline K. Burns, and James P. Syvertsen
, 2004 ), the lack of leaf abscission was likely due to night temperatures below 10 °C for 4 consecutive days after the 20 Dec. 2005 application. Fig. 1. Effects of 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP) and ethephon on mature fruit ( A
Robert C. Ebel, Jacqueline K. Burns, Kelly T. Morgan, and Fritz Roka
al., 1986 ; Yuan et al., 2005 ). A commercial label for the abscission agent 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) is being actively pursued by the commercial citrus industry in Florida. CMNP has been shown to increase fruit removal and
Luis Pozo and Jacqueline K. Burns
The use of the abscission agent 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP) in combination with mechanical harvesting increases mature sweet orange fruit removal without causing phytotoxicity to leaves and young developing fruit through most of
R. E. Holm and W. C. Wilson
Two and 3-way combinations of 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), cycloheximide (Acti-Aid), and chlorothalonil (Sweep) were extensively evaluated for fruit abscission and ethylene production responses on ‘Hamlin’ and ‘Valencia’ oranges (Citrus sinensis (L.) Osbeck). The combinations interact synergistically resulting in far greater fruit loosening than would be expected from additive effects of the individual chemicals. The 3-way combinations of Release plus Acti-Aid plus Sweep consistently gave better fruit abscission than the 2-way combinations of Release plus Acti-Aid and required 25% to 50% less abscission chemical compared to individual abscission chemical usage. Increased fruit abscission activity of the chemical combinations resulted from greater peak fruit ethylene production and higher sustained ethylene levels during the treatment period. Distinct fruit loosening and retightening phases were characterized and shown to be correlated with internal fruit ethylene levels.
Rongcai Yuan and Jacqueline K. Burns
The effect of temperature on the ability of 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) and ethephon to induce ethylene evolution and abscission of mature fruit and leaves was determined using 3-year-old potted `Hamlin' orange [Citrus sinensis (L.) Osb.] trees in environment-controlled growth rooms in seasons 2001-02 and 2002-03. Ethylene evolution and abscission of CMNP or ethephon-treated fruit and ethephon-treated leaves were highly temperature dependent. Fruit detachment force (FDF) and fruit ethylene evolution were not affected by application of ethephon at 200 mg·L-1 or CMNP at 200 mg·L-1 when air temperature was 10 °C for ethephon treatment or ≤15.6 °C for CMNP treatment. However, ethylene evolution of CMNP or ethephon-treated fruit increased sharply, and FDF decreased drastically as temperature increased from 10 to 26.7 °C for ethephon treatment or from 15.6 to 26.7 °C for CMNP treatment. Several 10 hour day/14 hour night temperature regimes were explored to determine the effect of varying daily and nightly temperatures on efficacy and ethylene evolution. At least 3 days of exposure to 21/10 °C were required for CMNP to effectively loosen fruit, whereas only one day of exposure to 26.7/15.6 °C was enough to induce similar changes. At 21/10 °C, CMNP significantly reduced FDF to<25 N and markedly enhanced fruit ethylene evolution, regardless of interruption by 1 day of low temperature at 10/10 °C in the first 5 d after application. Ethephon had no significant effect on leaf ethylene evolution and leaf abscission when temperature was 10 °C, but caused a marked increase in both leaf ethylene evolution and leaf abscission as temperature increased from 10 to 26.7 °C. CMNP did not stimulate leaf ethylene evolution and leaf abscission regardless of temperature. Chemical names used: 5-chloro-3-methyl-4-nitro-1 H-Pyrazole (CMNP); 2-chloroethylphosphonic acid (ethephon).