Chemical control of root deflection and tap root elongation in containerized nursery stock

These studies were designed 1. to test the effectiveness of a 7% cupric hydroxide [Cu(OH)₂]/latex paint formulation (Spin Out™) to control root deflection in a wide assortment of containerized nursery stock, and 2. to control tap root elongation of selected coarsely rooted species by inserting six different types of materials painted with Spin Out™ or impregnated with Spin Out™ WP (wetable powder) at the bottom of the container.

Seedlings or rooted cuttings of 54 taxa of ornamental trees, shrubs, perennials and grasses were grown in plastic containers, half of which were painted inside with Spin Out™. Root deflection was measured subjectively by a panel of four judges using a scale from 1 to 5, with 1 indicating root deflection of less than 1.3 cm, (excellent control) and 5 indicating severe root deflection (no control). While excellent control of root deflection was not always achieved in treated containers, root deflection was consistently reduced compared to untreated containers. This eliminated the need for corrective root pruning. Treatment means ranged from 1.0 to 2.5 with 83% ≤ 1.5. Control means ranged from 1.8 to 5.0 with 85% ≥ to 3.0. No visual signs of copper toxicity were observed. Cupric hydroxide did not inhibit or restrict the growth of stem structures such as rhizomes, stolons or basal suckers.

Tap roots of three coarse rooted species, Nyssa sylvatica Marshall (black gum), Quercus acutissma Carruth. (sawtooth oak) and Castanea mollissima Bl. (Chinese chestnut) were subjected to six treatment materials which were either cut to fit or placed on the bottom of a 7.6 1 container. Each treatment material (paint only, Styrofoam plug tray, 3M floor buffer mat, peat fiber sheet, stone and weed barrier fabric) was either painted with Spin Out™ or impregnated with Spin Out™ WP. Treatments that allowed the tap root to penetrate the material, i.e. weed barrier fabric, stone and 3M floor buffing mat, were more effective in controlling tap root elongation compared to controls. Weed barrier fabric significantly reduced tap root length of Quercus acutissima and Nyssa sylvatica by 80% and 67%, respectively, compared to controls and by 65% and 53%, respectively, compared to the paint only treatment. In some cases the 3M floor buffing mat and stone treatments were more effective than the weed barrier fabric but were impractical because of weight or expense. The interior walls of all treatment containers were painted with Spin Out™ which significantly inhibited lateral root deflection down the side of the container compared to controls.