COPPER HYDROXIDE-TREATED POTS IMPROVE THE ROOT SYSTEM OF BOUGAINVILLEA CUTTINGS

The responses of root systems of 'Barbara Karst' bougainvillea [Bougainvillea x buttiana (Bougainvillea glabra Choicy x Bougainvillea peruviana Humb. & Bonpl.) 'Barbara Karst'] cuttings to 100 g Cu(OHyiiter in latex paint applied to the interior surface of square 66, 120, or 280-ml plastic pots were determined. Cuttings (10 cm long; 3-5 nodes; 2 leaves) were scored on opposite sides and dipped in KIBA at 6000 mgliter1 for 3 sec on 16 Apr. 1993. Cuttings were placed in treated or untreated pots that contained a medium of 1 Canadi an sphagnum peat: 1 coarse perlite (v/v). The pots were com pletely randomized in a 3X2 factorial design. The cuttings were rooted under intermittent mist 9 sec-5 min1 for 12 hrday1 in a greenhouse (20% shade). Cuttings rooted in Cu(OH)2-treated containers had no root circling and a more compact, wellbranched root system compared to cuttings rooted in untreat ed containers. However, root fresh weight was reduced by the Cu(OH)2 treatment. Container size affected the number of pri mary roots as well as root fresh and dry weight. Bougainvillea are primarily propagated by stem cuttings. The cuttings root well but the root systems are usually com posed of long brittle non-fibrous roots which circle the interi or of the propagation container. When transplanted some of the roots are often broken. The results of recent studies have demonstrated the use fulness of chemical root pruning with copper hydroxide (Ar nold, 1992; Arnold et al., 1993; Svenson and Broschat, 1992). A relatively new product, Spin OutTM, is a water-based latex paint containing copper hydroxide that is applied to the inteFlorida Agricultural Experiment Station Journal Series No. N-01009 The authors gratefully acknowledge Griffin Corporation for their dona tion of SpinOutTM and Ms. Lucy Rogers and Mr. Judd Butler for their techni cal assistance. rior of containers. Root pruning occurs at the interface of the root tip and the copper-treated interior surface of the con tainer. Root circling, matting, and kinking are eliminated or reduced in many species (Appleton and Salzman, 1993; Ar nold, 1992; Arnold et al., 1993; Arnold and Struve, 1993; Beeson and Newton, 1992; Case and Arnold, 1992). When these negative root growth habits are controlled, rooting increases within the media. This results in a more evenly distributed root system which provides the opportunity for increased wa ter and nutrient uptake (Arnold and Struve, 1993). The objective of this study was to determine the effect of application of copper hydroxide to three different-sized con tainers on root system development of bougainvillea cuttings. Materials and Methods Softwood stems cuttings were removed from 'Barbara Karst' bougainvillea [Bougainvillea x buttiana (Bougainvillea glabra Choicy x Bougainvillea peruviana Humb. & Bonpl.) 'Bar bara Karst'] on 16 Apr. 1993 and submerged in a mixture of insecticidal soap (Safer, Wellsley, Mass.) (19.5 ml-liter"1) and dimethyl [ (1,2-phenylene)-bis (iminocarbonothioyl) ] bis(carbamate) (thiophanate-methyl; Domain FL; OM Scott, Marysville, Ohio) (1.3 ml-liter1). Cuttings (10 cm long; 3-5 nodes; 2 leaves) were scored on two sides and dipped in KIBA at 6000 mg-liter"1 for 3 sec. The cuttings were placed in one of three containers treated on the interior with Cu(OH)2/liter (in latex paint; Spin OutTM, Griffin Corp., Valdosta, GA) and filled with a medium of 1 Canadian sphagnum peat: 1 coarse perlite (v/v). Container sizes were 66 ml (4.5 cm square top, 4 cm bottom, and 3.7 cm deep), 120 ml (5 cm square top, 4.3 cm bottom, and 6 cm deep), and 280 ml (7 cm square top, 6 cm bottom and 7 cm deep). The containers, with and without Cu(OH)2, were completely randomized in a factorial experiment with 15 replications per treatment per container size. The cuttings were rooted under intermittent mist 9 sec-Smin'1 for 12 hr-day"1 in a greenhouse (20% shade). The number of primary roots, root fresh and dry weights, and degree of rooting were recorded 15 June. The degree of root ing was rated on a scale of l=no callusing, 2=only callusing, 3, 4, and 5=light, medium, and heavy rooting, respectively. Proc. Fla. State Hort. Soc. 107: 1994. 215 Figure 1. Root pruning effect on two-month-old 'Barbara Karst' bougain villea cuttings of a formulation of Cu(OH)2 in latex paint (Spin OutTM) ap plied to the interior surface of a 120-ml plastic container (A Untreated, B -