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Robert C. Ebel, Jacqueline K. Burns, and Kelly T. Morgan

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

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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

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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

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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.

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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

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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

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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

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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).

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Jacqueline K. Burns, Louise Ferguson, Kitren Glozer, William H. Krueger, and Richard C. Rosecrance

mg·L −1 dikegulac (Atrimmec; PBI/Gordon Corp, Kansas City, MO); or 1000 or 2000 mg·L −1 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP; previously formulated by Abbott Laboratories, Libertyville, IL). Maximum, minimum, and average temperatures on the

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Jacqueline K. Burns, Richard S. Buker III, and Fritz M. Roka

An abscission agent [5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP)] was applied to `Hamlin' and `Valencia' orange (Citrus sinensis) trees at concentrations ranging from 0 to 500 ppm in a volume of 300 gal/acre. Four days after application, fruit were mechanically harvested with either a trunk shake-and-catch or a continuous canopy shake-and-catch system commercially used in Florida. Harvesting conditions were varied by limiting the actual trunk shake time of the trunk shaker to 2, 4, or 7 seconds, or by altering the ground speed of the canopy shaker (1.0, 1.5, or 2.0 mph). In general, increasing duration of shake and the application of CMNP increased percent mature fruit removal and decreased the amount of fruit remaining in the tree. Increasing CMNP concentration decreased fruit detachment force but increased post-spray fruit drop. Comparison of short duration shake times in CMNP-applied trees with trees harvested at longer durations either sprayed or not sprayed with CMNP indicated no significant difference in percent mature fruit removal. The results demonstrate that CMNP application increases harvesting capacity of trunk and canopy shakers by reducing time necessary to harvest each tree while maintaining high percent mature fruit removal.