Tropical soda apple (Solanum viarum) herbicide susceptibility and competitiveness in tall fescue (Festuca arundinacea)

Tropical soda apple (TSA) was evaluated for response to 28 herbicide treatm ents. Treatments containing picloram or triclopyr controlled eight-leaf, 16 -leaf, and 1-yr-old TSA greater than 90% 8 wk after treatment (WAT). Contro l 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, p opulations of 0, 1, 2, 4, 8, 16, 32, and 64 TSA plants/700 cm(2) of tall fe scue had no effect on tall fescue height. TSA height was affected by TSA po pulation, and intraspecific TSA competition was expressed as etiolation at densities greater than 4 plants/700 c(m). Averaged over five periods of com petition, predicted yield losses of tall fescue were 14, 16, 29, and 31% an d 1, 11, 19, and 23% for 8, 16, 32, and 64 TSA plants/700 cm(2), respective ly, for each experiment. Differences in tall fescue dry matter response bet ween experiments were attributed to ambient temperature. Dry matter per ind ividual TSA plant decreased from 1.7 to 0.3 g as TSA density increased from 1 to 64 plants/700 cm(2). Percent canopy coverage of TSA relative to an ar ea of 700-cm(2) surface increased proportionally as tall fescue coverage de creased. After 10 wk of competition, TSA monopolized the canopy with covera ge of 92 and 94%; tall fescue coverage was limited to only 7 and 5% in expe riments I and II, respectively.