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Open access

W. H. deSilva, P. F. Bocion, and H. R. Walther

Abstract

Foliar application of 0.4 to 0.6% of an aqueous solution of sodium 2,3:4,6-di-O-isopropylidene-2-keto-L-gulonate) (dikegulac, Atrinal) was effective as a pinching agent under commercial growing conditions on all azalea (Rhododenron simsii Planch.) cultivars tested. One to 2 weeks after application the upper leaves turned yellow. Within 4 weeks after treatment the axillary shoots began to elongate and 4-8 weeks later the foliage regained a dark green color. Reproductive shoots treated with dikegulac produced new axillary shoots, but treatment should precede flower initiation for optimal results. At all dosage rates a better pinching effect was obtained with higher spray volumes. A spray volume of 200-300 ml/m2 (2-3 qts/100 ft2), depending on growth stage, is suggested. Dikegulac is a very promising chemical pinching agent for greenhouse azaleas.

Open access

G. Jay Gogue and H. Paul Rasmussen

Abstract

Chrysanthemum morifolium (Ramat.) cultivars showed a range of stem girdling responses when treated with the chemical pinching agents, a commercial pinching agent (OSO) and methyl decanoate (MD). Differential responses were attributed to the number of trichomes per unit area of the stem; resistant cultivars had more trichomes than susceptible cultivars. The stomatal number per unit of stem area was constant for all cultivars. Stem diameter was not a significant factor in the susceptibility of cultivars to girdling damage. Resistance was eliminated by damaging or removing the trichomes of a resistant cultivar. Similar treatment of a susceptible cultivar did not increase susceptibility. Susceptible cultivars absorbed more 14C MD than resistant ones. Injury was positively correlated with 14C MD uptake within cultivars. Methyl decanote did not enter the stem through epidermal cells adjacent to trichomes or the trichome itself, but rather through epidermal cells not in proximity of the trichomes.

Free access

Jeffrey G. Norcini and James H. Aldrich

The response of `Barbara Karst' bougainvillea to the chemical pinching agent Off-Shoot-O® (OSO; methyl esters of fatty acids), was evaluated. Liners were transplanted 4 Apr. 1994 into 3.8-liter containers of soilless medium. OSO at 0 (+pruning), 7.8, 15.6, 31.2, 62.5, 125, and 250 ml·liter–1 was applied over the top on 24 May to 20 replications per OSO concentration and 10 replications per control. On 25 May, OSO was reapplied to 10 replications per OSO concentration. Treatments were applied using a compressed-air backpack sprayer that delivered 82 + 3 and 93 ± 2 liter·ha–1 at 2.8 kg·cm–2 on 24 and 25 May, respectively. Crown phytotoxicity was recorded 1, 2, 7, and 13 days after the initial application on a scale of 0 = no injury to 10 = plant death. A growth index and number of stems <5, 5 to <10, 10 to <15, and >15 cm long were recorded 23 May and 7 July. The best overall response was to the 15.6 + 15.6 ml·liter–1 application, despite the slight but commercially acceptable foliar injury (mean rating = 2.3+0.2). This treatment was similar to the pruned control in growth and number of stems.

Open access

William E. Brabson Jr. and Richard S. Lindstrom

Abstract

Off-Shoot-O (emulsified methyl esters of fatty acids) applied to azalea plants (Rhododendron indicum Sweet and R. obtusum Plauch cvs. Coral Bells, Red Wing, and Gloria) induced a chemical pinch to replace the hand pinching operation. There was no evidence which directly related air movement to a positive pinch, although there were trends which indicated differences from one season of the year to another. There were no differences in pinching action due to light intensity regimes.

Temperature was the major factor determining a positive chemical pinch. Plants pre-conditioned at low temp were more sensitive to the chemical pinching agent than were plants pre-conditioned at high temp.

Open access

Lawson H. Carr and Richard S. Lindstrom

Abstract

The influence of environmental and morphological factors on chemical pinching of greenhouse azaleas with methyl esters of fatty acids (C6 - C12) was investigated. No air movement around the plants, following treatment, induced more bud necrosis than air movement; but the trends were not consistent within monthly treatments between cultivars or within a cultivar from month-to-month. Plants pre-conditioned at night/day (N/D) temp of 10/15.5°C from 1-7 days were found to have a greater response to the chemical pinching than when pre-conditioned at high temp at 26.6/32.2°C (N/D). The age of the terminal shoot influenced the response to the pinching agent. Plants with shoots 4 to 6 weeks of age were more sensitive to chemical pinching than those with 3,7, and 8 week shoots. Low relative humidity (RH 30%) and low temp (10/15.5°C, N/D) resulted in increased bud necrosis when compared with 60 and 90% RH at high temp (26.6/32.2°C, N/D).

Open access

D. Palevitch and E. Pressman

Abstract

Several chemical pinching agents tested in the greenhouse inhibited terminal bud growth and stimulated side shoot growth of broccoli (Brassica oleracea L. Italica group). The most effective materials were n-decanol and two commercial producta which were combinations of 45% methyl esters of fatty acids (Emgard = 4% C8, 94% C9, 2% C10 and Off Shoot 0 = 4% C6, 56% C8, 38% C10, 2% C12). More side shoots suitable for processing developed in the chemically-treated plants than in the hand-pinched plants. In the field both of the two materials tested, Emgard and n-decanol, inhibited terminal inflorescences but n-decanol was more effective.

Open access

Lih-Jyu Shu, Kenneth C. Sanderson, and J. C. Williams

Abstract

Applications of 0.5% dikegulac sodium (sodium salt of 2,3:4,6-bis-0-(l-methylethylidene-L-xylo-2-hexulofu-ranosonic acid) sprays produced significantly more new shoots on ‘Red wing’ or ‘King fisher’ azalea plants than manual pinching and other chemical pinching agents in 2 experiments. In 5 other experiments involving 5 other cultivars, dikegulac sodium-treated plants generally produced the most shoots, however, the shoot number was not different from shoot number on either manually pinched or 4.2% Off-Shoot-O-treated (mixture of C6 to C12 methyl ester of fatty acids) plants. Sprays of dimethyl dodecylamine caprylate at 0.2% and 0.5%, n-decanol at 2.5%, ethephon [(2-chloroethyl)phosphonic acid)] at 0.08%, and UBI-P293 (2,3-dihydro-5,6-diphenyl-1,4-oxathiin) at 1.0% gave inconsisent results but yielded shoot number comparable to dikegulac sodium in some tests. Off-Shoot-O, dimethyl dodecylamine caprylate, and n-un-decanol were destructive pinching agents at some concentrations and caused considerable plant injury. Dikegulac sodium caused minor injury and transient chlorosis. Ethephon, PBA [6-benzylamino-9(2-tetrahydropyran-2-yl)-9H-purine], and UBI-P293 did not produce any visible phytotoxicities. Shoots of plants sprayed with 0.5% dikegulac sodium and 1.0% UBI-P293 were of similar length or shorter than shoots of either manually pinched or untreated check plants 3 weeks after treatment.

Open access

Mason Marshall, Terri Starman, H. Brent Pemberton, and Calvin Trostle

labor-intensive practice that can become costly for growers ( Cheema, 2018 ; Starman, 1991 ). Meijón et al. (2009 ) noted that chemical pinching agents can reduce the cost associated with manual pinching, but the plant growth response is variable

Open access

A. J. Lewis III

Abstract

Foliar sprays of undecanol increased branching in some cultivars of Euphorbia pulcherrima Willd. compared to unpinched controls, but did not increase branching compared to manually pinched plants. However, phytotoxicity at concentrations necessary to achieve these results made the plants marketably unacceptable.

Open access

A. J. Lewis III and J. R. Haun

Abstract

Ethyl hydrogen 1-propylphosphonate (EHPP) applied to Ilex crenata, Thunb. ‘Hetzi’ increased the number of branches. The optimum concentration for branching was 4000 ppm. Higher concentrations reduced branching, produced phytotoxicity, and delayed regrowth. Plant dry weight was inversely proportional to concentration at rates above 2000 ppm.