Roundup over the Top of Container-Grown Nursery Plants
Type of Degreethesis
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Nine species of container-grown plants were treated over-the-top with Roundup Pro® at 4 rates: 0.28, 0.56, 1.12, and 2.24 kg ai/ha (0.25, 0.5, 1.0 and 2.0 lb ai/A) once in June 2007, September 2007, or February 2008. A fourth group was treated on all three dates (JSF). The experiment was repeated on eight species in 2008-2009. Growth indices (GI) were taken before the spring growth flush in March 2008 and after the first growth flush in June. In experiment one, 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 rates up to 1.12 kg ai/ha (1.0 lb ai/A) applied singly or JSF, except for temporary injury on ‘Blue Pacific’ from Feb applications. The remainder of the species had reduced growth as Roundup Pro® rates increased. ‘Blue Rug’ juniper (J. horizontalis ‘Wiltonii’) was tolerant in Feb but injured at ≥ 1.12 kg ai/ha (1.0 lb ai/A) in June and Sept (JS). Asiatic jasmine (Trachelospermum asiaticum) was tolerant of single applications at rates ≤ 1.12 kg ai/ha (1.0 lb ai/A) in JS, but showed stunting of new foliage from all Feb applications. Dwarf yaupon (Ilex vomitoria ‘Stoke’s Dwarf’) showed injury at 74 DAT after June applications, no injury at rates ≤ 1.12 kg ai/ha (1.0 lb ai/A) in Sept, and stunting and delay of new foliage from all Feb applications and rates ≥ 0.56 kg ai/ha (0.5 lb ai/A) in June. ‘Pink Gumpo’ azalea (Rhododendron eriocarpum ‘Gumpo Pink’) was injured by rates ≥ 1.12 kg ai/ha (1.0 lb ai/A) applied in June, Feb, and JSF. In experiment two, dwarf mondo and mondo tolerated all single application rates up to 1.12 kg ai/ha (1.0 lb ai/A). Asiatic jasmine was injured by all Feb treatments and growth was reduced and stunted by ≥ 1.12 kg ai/ha (1.0 lb ai/A) in Feb and JSF. Dwarf yaupon GI were reduced by rates ≥ 1.12 kg ai/ha (1.0 lb ai/A) in Feb, 2.24 kg ai/ha (2.0 lb ai/A) in June, and by all treatments in JSF. Feb treatments ≥ 0.28 kg ai/ha (0.25 lb ai/A) delayed shoot growth of dwarf yaupon for at least 6 weeks. ‘Hardy Daisy’ gardenia (Gardenia jasminoides 'Hardy Daisy’) showed slight injury from Feb rates ≥ 1.12 kg ai/ha (1.0 lb ai/A), but growth was reduced at 2.24 kg ai/ha (2.0 lb ai/A) for June and JSF. Sky pencil holly (Ilex crenata ‘Sky Pencil’) showed stunting from all Feb applications, but was tolerant up to 2.24 kg ai/ha (2.0 lb ai/A) in June and Sept; GI were similar for all treatments. Purpleleaf wintercreeper euonymus (Euonymus fortunei ‘Coloratus’) was injured by rates ≥ 1.12 kg ai/ha (1.0 lb ai/A) in June and JS, all Feb treatments, and stunted by two or three applications of 2.24 kg ai/ha (2.0 lb ai/A), but all other treatments had similar GI. Wintergreen boxwood (Buxus sempervirens ‘Wintergreen’) was injured at 2.24 kg ai/ha (2.0 lb ai/A) in June, ≥ 1.12 kg ai/ha (1.0 lb ai/A) in JS, and all Feb applications. Growth was reduced by rates of 2.24 kg ai/ha (2.0 lb ai/A) in Feb and ≥ 1.12 kg ai/ha (1.0 lb ai/A) in JSF. Three additional experiments were conducted to determine the effects of repeated applications of Roundup Pro® over the top of container-grown nursery crops. Plants were treated with single applications of Roundup Pro® at 1.12 kg ai/ha (1.0 lb ai/A) in July, August, September, or October, 2008 or 2009. Other plants were treated in July and August ; July, August, and September; July, August, September, and October; or July and September. Experiment 1 (2008): Liriope muscari ‘Big Blue,’ Camellia sasanqua ‘Shishigashira,’ and Gardenia jasminoides ‘Radicans’ were evaluated. ‘Big Blue’ liriope showed minor injury from multiple applications with reduced growth from 3 or 4 applications, but all plants were marketable in June of the following season. Camellia exhibited no injury from any Roundup application and all parameters were similar to controls. ‘Radicans’ gardenia showed fall chlorosis and stunting through early spring from multiple applications, but all plants were marketable, with those treated 3 or 4 times rated small but marketable. Experiment 2 (2009, Auburn): ‘Big Blue’ liriope, ‘Radicans’ gardenia, C. sasanqua ‘Martha Simms,’ and Juniperus conferta ‘Blue Pacific,’ showed no injury from any treatment and growth indices in January and June were similar to controls. Ilex cornuta ‘Dwarf Burfordi’ growth indices were similar to controls with occasional chlorosis seen after July treatments. Ternstroemia gymnathera (cleyera) exhibited chlorosis, necrosis, and stunting of shoot tips for all treatments, but regrowth was similar to controls for all treatments the following spring. All plants were vigorous and marketable. Experiment 3 (2009, Mobile, AL): ‘Big Blue’ liriope, ‘Radicans’ gardenia, ‘Blue Pacific juniper, I. cornuta ‘Carissa,’ and cleyera growth indices were similar to controls in February and late May. Slight injury occurred only on the new growth of cleyera and carissa holly with primary symptoms being chlorosis and/or slight stunting seen in mid-September and October from some single and double applications. Results of the rate and timing study for plants treated in June, September, or February or all three dates demonstrated that dwarf mondo, liriope ‘Cleopatra’ and ‘Variegata,’ and ‘Blue Pacific’ juniper were tolerant to single or multiple rates up to 2 lb ai/A and were not affected by time of year, except for ‘Blue Pacific,’ which was temporarily injured by spring applications at rates ≥ 0.5 lb ai/A but recovered quickly. Mondo grass was tolerant up to 1.0 lb ai/A in February and multiple applications and up to 2.0 lb in June or September. ‘Blue Rug’ juniper was tolerant of rates up to 2 lb applied in February but injured or stunted by rates ≥ 1.0 lb ai/A in June and September. All plants in experiment 1 except ‘Blue Rug’ juniper and all in experiment 2 were tolerant up to 2 lb when applied in September. Results for the repeated application studies demonstrated that all growth indices for ‘Big Blue’ liriope, ‘Radicans’ gardenia, camellia ‘Martha Simms,’ ‘Blue Pacific’ juniper, dwarf burford holly, carissa holly, and cleyera were similar to non-treated controls in experiment 2 and 3 of this study regardless of the number of treatments, with the exception of cleyera in experiment 2. Data showed that plants were more tolerant as they were treated later in the season. All plants treated once or multiple times with 1.0 lb ai/A Roundup Pro® in July through October were marketable at the end of the following spring flush. Data also showed that regrowth the following year was similar to controls with up to 4 applications of 1.0 lb ai/A applied 28 days apart. Despite the fact that multiple applications caused lower growth indices on ‘Radicans’ gardenia and ‘Big Blue’ liriope in experiment 1 and cleyera in experiment 2 of this series, plants were marketable the following year.