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Matthew W. Fidelibus, Kimberley A. Cathline, and Jacqueline K. Burns

mature grape berries. To identify new potential abscission agents for grape, candidate compounds were obtained that met one or more of the following criteria: registered for use on other fruit crops, have the potential to be cost-effective, or may be

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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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Naveen Kumar and Robert C. Ebel

spongy albedo. However, calyx AZ is situated deeper within the albedo tissue and could be visually identified ( Brown and Burns, 1998 ). CMNP is a pyrazole compound and demonstrated as a potential nontoxic abscission agent for the late season ‘Valencia

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Timothy M. Spann, Luis V. Pozo, Igor Kostenyuk, and Jacqueline K. Burns

have been underway to find a viable way to harvest ‘Valencia’ orange fruit after 1 May without impacting subsequent year yields. The abscission agent CMNP effectively loosens mature citrus fruit without affecting immature fruit, allowing mechanical

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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.

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Brian A. Kahn, James E. Motes, and Niels O. Maness

Mechanical harvest of paprika pepper (Capsicum annuum L.) produces a mixture of marketable and unmarketable fruit. Our objective was to increase the percentage of marketable red fruit in a once-over harvest by using ethephon to remove late-developing flower buds, blooms, and green fruit. Three experiments were conducted on field-grown plants in southwestern Oklahoma. We tested ethephon solutions of 0, 1000, 2000, 3000, and 4000 μL·L-1 as a one-time foliar application on various dates in September and October. Total dry mass of harvested fruit decreased linearly as ethephon rate increased in all experiments. Marketable fruit, as a percentage of total harvested fruit mass, increased linearly with ethephon rate in two of three experiments. Ethephon decreased the percent of total harvested fruit mass due to green fruit in all experiments. We recommend a single application of ethephon at about 2000 to 3000 μL·L-1 as a controlled abscission agent to increase the percentage of harvested red fruit in paprika pepper. The precise timing of the application will vary with the situation, but the last 10 days in September seemed an appropriate interval for southwestern Oklahoma. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

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Jacqueline K. Burns, Fritz M. Roka, Kuo-Tan Li, Luis Pozo, and Richard S. Buker

An abscission agent (5-chloro-3-methyl-4-nitro-1H-pyrazole [CMNP]) at 300 mg·L–1 in a volume of 2810 L·ha–1 was applied to Valencia orange trees [Citrus sinensis (L.) Osb.] on 22 May 2004. At this time, immature and mature fruit were present on the tree simultaneously. Three days after application, fruit were mechanically harvested using a trunk-shake-and-catch system. The power to the shaker head was operated at full- or half-throttle (FT or HT, respectively), and the duration of trunk shaking was 2 seconds at FT or 4 seconds at FT and HT. Mature fruit removal percentage and number of immature fruit removed, and fruitlet weight and diameter were determined. Mature fruit removal percentage with 2 seconds at FT or 4 seconds at FT harvesting ±CMNP, or 4 seconds at HT + CMNP was not significantly different and ranged between 89% to 97%. Harvesting at 4 seconds HT without CMNP removed significantly less mature fruit than any treatment. CMNP did not affect immature fruit removal by the trunk shaker. Harvesting at 4 seconds at HT removed significantly less immature fruit than 2 seconds at FT or 4 seconds at FT. No significant difference in fruitlet weight or diameter was measured between any trunk shaker harvest operation and CMNP treatment. Trunk shaking frequency was estimated to be 4.8 and 8.0 Hz at HT and FT, respectively. Yield in 2005 was determined on the same trees used for harvest treatments in 2004. CMNP did not impact yield. No significant difference in yield was seen between the hand-picked control and 4 seconds at HT, whereas yield in the remaining treatments was lower. The results demonstrate that CMNP application combined with low frequency trunk shaker harvesting can achieve high percentage of mature fruit removal with no significant impact on return yield of the following crop.

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Jacqueline K. Burns, Luis V. Pozo, Rongcai Yuan, and Brandon Hockema

Guanfacine and clonidine were combined with ethephon or metsulfuron-methyl in the spray tank and applied as foliar sprays to Citrus sinensis L. Osb. `Valencia', Citrus madurensis Loureiro (calamondin), and Prunus persica `Elberta' to determine their effects on leaf loss, fruit detachment force (FDF), immature fruit loss, and twig dieback. In `Valencia' orange, `Elberta' peach and calamondin, guanfacine and clonidine effectively reduced ethephon-induced defoliation in all three tree species, whereas only guanfacine was effective with metsulfuron-methyl applications in `Valencia'. The ability of ethephon to reduce FDF in `Valencia' was only minimally impaired by guanfacine but not impaired by clonidine. Both guanfacine and clonidine diminished the capacity of metsulfuron-methyl to reduce FDF. Guanfacine reduced immature fruit loss of `Valencia' caused by metsulfuron-methyl and reduced twig-dieback. Leaf loss was reduced whether guanfacine or clonidine were applied with ethephon, or 24 hours or 17 days before ethephon application. Guanfacine and clonidine reduced leaf loss induced by continuous exposure of potted calamondin trees to ethylene, and leaf loss was similar with guanfacine and 1-methylcyclopropene (1-MCP) treatments. In separate experiments, guanfacine and clonidine were unable to block ethylene perception in Arabidopsis seedlings and petunia flowers but promoted rooting in coleus and tomato vegetative cuttings, suggesting that these compounds have auxin-like activity. The results demonstrate the potential to enhance selectivity of abscission agents with guanfacine and clonidine. Chemical names used: 2-[(2,6-dichlorophenyl)amino]-2-imidazoline, clonidine; 5-chloro-3-methyl-4-nitro-pyrazole, CMN-P; [(2,6-dichlorophenyl)acetyl]guanidine, guanfacine; [(2-chloroethyl)phosphonic acid, ethephon; indole-3-butyric acid, IBA; 1-methylcyclopropene, 1-MCP.

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

together down the tree row shaking both sides of each tree until the decks are full, at which point they stop and unload the fruit through a conveyor into the bed of a truck that remove the fruit from the grove. There are no abscission agents that are

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

A study was initiated in `Hamlin' orange to determine if a selective citrus abscission material, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP), could improve mature fruit removal and recovery when used with mechanical harvesters. A trunk shaker and continuous-moving canopy shaker equipped with catch-frames were used at the flatwoods and ridge growing regions in Florida. Both trials were conducted during the first 2 weeks of Dec. 2003. Plots were constructed as randomized complete blocks containing four replicates for each treatment. Each replicate contained five trees at the ridge site or four trees at the flatwoods site. CMNP was applied using a commercial airblast sprayer at 0, 125, 250 and 500 mg·L-1 at a rate of 2,800 L·ha-1 4 days before scheduled harvest. The trunk shaker was operated for either 7 seconds or 2 seconds/tree, whereas the canopy shaker was operated at either 260 cpm or 140 cpm/tree. The data show that the correct time was selected for harvest. Over a 50% reduction in FDF was achieved with the 250 and 500 mg·L-1 treatments, while post-application fruit drop was less than 1.5%. The greatest benefit of abscission agent use was seen when the mechanical harvesters were operated at the least aggressive setting (2 seconds or 140 cpm), where increases in % fruit removal and recovery were over 20% higher than the controls. At the most aggressive settings, numeric increases in % fruit removal and recoveries were measured, but these changes were not statistically significant. The results demonstrated that statistically similar % fruit removal and recoveries could be achieved using less aggressive harvester settings with abscission agent use when compared with most aggressive settings using no abscission agent.