Paclobutrazol Sprays Research Articles

Chemical Control of Vegetative Growth in Citrus Trees by Paclobutrazol

Abstract Paclobutrazol (PP333) [(2RS,3RS)-l-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl-)pentan-3-ol] sprays applied to ‘Minneola’ tangelo trees, at 500 or 1000 ppm, before the onset of summer flush, markedly reduced total growth, number of shoots, and internode length. Soil treatments (0.4 and 0.8 g per square meter) had only a small effect, probably because of the short time from application to flush inception. Sprays of Morphactin (an auxin transport inhibitor), at 250 and 500 ppm did not reduce growth, but rather enhanced it by increasing the number of emerging shoots. The spring flush of the same trees also showed effects of paclobutrazol soil treatments, whereas other treatments were not different from control. Paclobutrazol sprays on comparable ‘Minneola’ trees just before the spring flush also reduced this growth. Paclobutrazol may become a tool for the control of vegetative growth of mature citrus trees.

Comparison of a new triazole retardant paclobutrazol (PP 333) with ancymidol, chlorphonium chloride, daminozide and piproctanyl bromide, on stem extension and inflorescence development in Chrysanthemum morifolium Ramat

Several experiments in glasshouses at different times of the year have demonstrated that a new growth retardant, paclobutrazol (PP 333), applied as a single compost drench or as a foliar spray, is very effective in controlling stem extension in the pot chrysanthemum ( Chrysanthemum morifolium) ‘Bright Golden Anne’, a tall cultivar. Moreover, the concentration required, 30–50 mg a.i. l −1, was much lower than with a drench of chlorphonium chloride (Phosfon/Phosfleur), or with a foliar spray of daminozide (Alar/B-Nine) or piproctanyl bromide (Alden/Stemtrol). In two trials, a comparison of paclobutrazol and ancymidol (A-Rest/Reducymol) drenches indicated that, on a weight basis, the two compounds induced approximately equal dwarfing, whereas foliar sprays of paclobutrazol were more active than those of ancymidol, particularly at the lower concentrations. As before, at least 50–100 times the concentration of daminozide was needed than of paclobutrazol or ancymidol in order to induce an equivalent response. However, the variability in lateral stem length within a pot of 12 flowering shoots was a little higher with foliar sprays of paclobutrazol than with daminozide, possibly indicating that the amount of paclobutrazol transported to its site(s) of action varied more between shoots. Paclobutrazol produced similar delays in flowering (which invariably accompany commercially adequate reductions in plant height) to ancymidol and daminozide, whereas the delays with chlorphonium chloride and piproctanyl bromide were 2–4 days greater. In an experiment with the dark pink ‘Regal Anne’, daminozide caused some loss of flower pigmentation, but paclobutrazol and the other compounds did not.

Chemical control of tree growth of plum (prunus domesticaL.). I. Preliminary studies with the growth retardant paclobutrazol (PP333)

SummaryFoliar sprays of paclobutrazol (PP333) reduced the total new shoot growth on three European plum cultivars. High-volume sprays (3 000 mg l-1 applied once, or 1 500 mg l-1 applied twice) in May or early June reduced the numbers of extension shoots on Grove’s Late Victoria and similar sprays to Laxton’s Cropper and Marjorie’s Seedling reduced the mean shoot length. Soil drenches of paclobutrazol (4 kg ha-1) applied in May also slightly reduced the current seasons’s shoot growth of Laxton’s Cropper and Marjorie’s Seedling; drenches applied to the former cultivar had an even stronger effect in the subsequent season. Two sprays of GA3 (75 mg l-1) + 2,4,5-TP (10 mg l-1) applied four and six weeks after 50% petal-fall, reversed the effects of paclobutrazol on shoot growth of Grove’s Late Victoria, but in the following season the growth of these trees was reduced. Foliar sprays of paclobutrazol severely reduced the yields of Grove’s Late Victoria and this effect was only partially alleviated by sprays of G...

The effects of paclobutrazol and daminozide on the growth and yield of cider apple trees

SummaryThe effects of soil applications (1, 2 or 4 kg a.i. ha-1 to give 0.25, 0.5 or 1.0 g a.i. per tree) or foliar sprays (1000 or 2000 mg l-1 to give 2 or 4 g a.i. per tree) of paclobutrazol (PP 333) were compared with those of foliar daminozide (Alar) sprays (2000 mg l-1 to give 4 g a.i. per tree) on bush cider apple cv Michelin for two years. Extension shoot growth was significantly reduced in the year of application (Year 1) by foliar paclobutrazol and daminozide sprays, and in the following year by the foliar and high-rate soil-applied paclobutrazol but not by daminozide. Foliar applications of paclobutrazol reduced leaf size and darkened leaf colour, delayed flowering and enhanced fruit set. Yields were not affected by any treatment.

Changes in fruit set, leaf size and shoot growth of apple caused by some fungicides, insecticides and a plant growth regulator

SummaryOf seven chemicals sprayed onto apple flowers before flowering or at petal-fall stage one fungicide (triadimefon) increased fruit set, and one insecticide (chlorpyriphos) and the growth regulator (paclobutrazol) decreased it. These three chemicals sprayed at green-cluster stage also reduced eventual leaf size. Later sprays of chlorphyriphos and paclobutrazol sometimes reduced, and gamma-HCH sometimes increased, bourse shoot growth.

Growth Retardation Activity of Paclobutrazol on Chrysanthemum

Abstract Height of potted chrysanthemums (Chrysanthemum × morifolium Ramat.) was effectively controlled by soil drench applications of paclobutrazol [ICI-PP-333 = (2RS, 3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-l,2,4-triazol-l-yl-pentan-3-ol]. While response to the chemical depended on normal flowering height of each cultivar, rates of 0.125–0.750 mg ai/15-cm pot were effective on the tall- and medium-height cultivars tested. Aqueous foliar sprays were ineffective in controlling plant height. Foliar sprays of paclobutrazol mixed in 15% ethanol caused significant height reduction of chrysanthemum. Foliar sprays were not as effective as soil drench applications for controlling growth.