Tropical Soda Apple (Solanum viarum) Herbicide Susceptibility and Competitiveness in Tall Fescue (Festuca arundinacea)1

Abstract

Tropical soda apple (TSA) was evaluated for response to 28 herbicide treatments. Treatments containing picloram or triclopyr controlled eight-leaf, 16-leaf, and 1-yr-old TSA greater than 90% 8 wk after treatment (WAT). Control of 1-yr-old TSA did not increase 8 WAT when triclopyr was mixed in diesel fuel rather than water. In greenhouse additive interference experiments, populations of 0, 1, 2, 4, 8, 16, 32, and 64 TSA plants/700 cm2 of tall fescue had no effect on tall fescue height. TSA height was affected by TSA population, and intraspecific TSA competition was expressed as etiolation at densities greater than 4 plants/700 cm2. Averaged over five periods of competition, predicted yield losses of tall fescue were 14, 16, 29, and 31% and 1, 11, 19, and 23% for 8, 16, 32, and 64 TSA plants/700 cm2, respectively, for each experiment. Differences in tall fescue dry matter response between experiments were attributed to ambient temperature. Dry matter per individual TSA plant decreased from 1.7 to 0.3 g as TSA density increased from 1 to 64 plants/700 cm2. Percent canopy coverage of TSA relative to an area of 700-cm2 surface increased proportionally as tall fescue coverage decreased. After 10 wk of competition, TSA monopolized the canopy with coverage of 92 and 94%; tall fescue coverage was limited to only 7 and 5% in experiments I and II, respectively.Nomenclature: Picloram, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid; triclopyr, [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid; tropical soda apple, Solanum viarum Dunal #3 SOLVI; tall fescue, Festuca arundinacea Schreb. # FESAR ‘Kentucky 31.’Additional index words: Additive competitive design, chemical control, herbicides, weed density, Solanum khasianum C. B. Clarke var. chatterjeeanum Sengupta, SOLVI.Abbreviations: TSA, tropical soda apple; WAT, weeks after treatment; WATP, weeks after transplanting.