Roundup Pro® Over the Top of Nursery Crops: Rates and Timing

Abstract

Nine species of container-grown plants were treated over-the-top with Roundup Pro® (41% glyshosate) at four rates: 0.28, 0.56, 1.12, and 2.24 kg ai·ha−1 (0.25, 0.5, 1.0 and 2.0 lb ai·A−1) either in June 2007, September 2007, or February 2008. A fourth group was treated on all three dates (June + September + February) (JSF). The experiment was repeated on eight species in 2008–2009. Growth indices (GI) were taken before the spring growth flush in March and after the first growth flush in June. In Exp. 1, dwarf mondo grass (Ophiopogon japonicus ‘Nana’), mondo grass (O. japonicus), liriope (Liriope muscari ‘Cleopatra’), variegated liriope (L. muscari ‘Variegata’), and ‘Blue Pacific’ juniper (Juniperus rigida subsp. conferta ‘Blue Pacific’) were not affected by glyphosate rates up to 1.12 kg ai·ha−1 (1.0 lb ai·A−1) applied singly or JSF, except for temporary injury on ‘Blue Pacific’ from February applications. The remainder of the species had reduced growth as Roundup Pro® rates increased. ‘Blue Rug’ juniper (J. horizontalis ‘Wiltonii’) was tolerant in February but injured at ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in June and September (JS). Asiatic jasmine (Trachelospermum asiaticum) was tolerant of single applications at rates ≤ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in JS, but showed stunting of new foliage from all February applications. Dwarf yaupon (Ilex vomitoria ‘Stoke's Dwarf’) showed injury at 74 days after treatment (DAT) after June applications, no injury at rates ≤ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in September, and stunting and delay of new foliage from all February applications and rates ≥ 0.56 kg ai·ha−1 (0.5 lb ai·A−1) in June. ‘Pink Gumpo’ azalea (Rhododendron eriocarpum ‘Gumpo Pink’) was injured by rates ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) applied in June, February, and JSF, however no injury occurred with any September treatment. In Exp. 2, dwarf mondo and mondo tolerated all single application rates up to 1.12 kg ai·ha−1 (1.0 lb ai·A−1). Asiatic jasmine was injured by all February treatments and growth was reduced and stunted by ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in February and JSF. Dwarf yaupon GI were reduced by rates ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in February, 2.24 kg ai·ha−1 (2.0 lb ai·A−1) in June, and by all treatments in JSF. February treatments ≥ 0.28 kg ai·ha−1 (0.25 lb ai·A−1) delayed shoot growth of dwarf yaupon for at least 6 weeks. ‘Hardy Daisy’ gardenia (Gardenia jasminoides ‘Hardy Daisy’) showed slight injury from February rates ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1), but growth was reduced at 2.24 kg ai·ha−1 (2.0 lb ai·A−1) for June and JSF. Sky pencil holly (Ilex crenata ‘Sky Pencil’) showed stunting from all February applications, but was tolerant up to 2.24 kg ai·ha−1 (2.0 lb ai·A−1) in June and September; GI were similar for all treatments. Purpleleaf wintercreeper euonymus (Euonymus fortunei ‘Coloratus’) was injured by rates ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) applied in June and JS, all February treatments, and stunted by two or three applications of 2.24 kg ai·ha−1 (2.0 lb ai·A−1), but all other treatments had similar GI. Wintergreen boxwood (Buxus sempervirens ‘Wintergreen’) was injured at 2.24 kg ai·ha−1 (2.0 lb ai·A−1) in June, ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in JS, and all February applications. Growth was reduced by rates of 2.24 kg ai·ha−1 (2.0 lb ai·A−1) in February and ≥ 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in JSF.