Effects of Repeated Applications of Roundup Pro® Over the Top of Container-Grown Nursery Crops

Abstract

Three experiments studying the effects of repeated over-the-top applications of Roundup Pro® to container-grown nursery crops were conducted. Plants in 3.8 liter (1 gal) containers were treated with either single or multiple applications of Roundup Pro® at 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in July, August, September, or October, 2008 or 2009. Plants treated with multiple applications were treated in July and August (J+A); July, August, and September (J+A+S); July, August, September, and October (J+A+S+O); or July and September (J+S). Injury ratings were taken at multiple times after treatments. Growth indices (GI) [(height + width1 + width2) / 3] were taken in January and June 2009 and February and May 2010. Plants were rated for vigor and marketability in May 2009 or June 2010. Liriope muscari ‘Big Blue,’ Camellia sasanqua ‘Shishigashira,’ and Gardenia jasminoides ‘Radicans’ were evaluated in Experiment 1 (2008, Auburn). Liriope showed minor injury from two or more applications with reduced growth from 3 or 4 applications, but all plants were rated as marketable in June of the following season. ‘Shishigashira’ camellia exhibited no injury from any glyphosate application and all parameters were similar to non-treated controls (NTC). Gardenia showed fall chlorosis and stunting through early spring from multiple applications, but all plants were marketable. Even those treated 3 or 4 times were small but marketable. In Experiment 2 (2009, Auburn. AL), ‘Big Blue’ liriope, ‘Radicans’ gardenia, Camellia sasanqua ‘Martha Sims,’ and Juniperus conferta ‘Blue Pacific’ showed no injury from any treatment and GI in January and June were similar to NTC. Ilex cornuta ‘Dwarf Burfordi’ GI were similar to NTC with occasional chlorosis observed after July treatments. Ternstroemia gymnathera (cleyera) exhibited chlorosis, necrosis, and stunting of shoot tips for all treatments. Cleyera GI in January and June indicated that J+A+S, J+A+S+O, and J+S-treated plants were smaller than NTC, but regrowth was similar to NTC for all treatments the following spring. All plants were vigorous and marketable. In Experiment 3 (2009, Mobile, AL), ‘Big Blue’ liriope, ‘Radicans’ gardenia, ‘Blue Pacific’ juniper, ‘Martha Sims’ camellia, Ilex cornuta ‘Carissa,’ and cleyera GI were similar to NTC 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.