Tropical soda apple control as influenced by frost and herbicides

Destruction of photosynthetic tissue by frost may predispose tropical soda apple (Solanum viarum Dunal) (TSA) to herbicides. Field studies were conduc ted in 1996 and 1997 to evaluate the influence of herbicides applied to TSA regrowth 60 d after a heavy frost (-4.2 degrees C). Treatments included tr iclopyr [(3, 5, 6-trichloro-2-pyridinyl) oxy acetic acid] at 0.6 (single), 0.6 + 0.6 (30 d sequential) and 1.1 kg ai ha(-1); hexazinone [3-cyclohexyl- 6-(dimethylamino)-1-methyl-1, 3, 5-triazine-2, 4 (1H, 3H-dione] at 0.6 and 1.1 kg ai ha(-1); 4, 4-D ester [Isooctyl (2-ethylhexyl) ester of 2, 4-dichl orophenoxyacetic acid] at 2.2 and 3.4 kg ai ha(-1); and an untreated check. Tropical soda apple control was recorded at monthly intervals starting at 60 d and terminating at 120 or 150 d, depending on the year. Applying herbi cides to TSA regrowth 60 d after a heavy frost resulted in excellent contro l. Triclopyr (0.6 + 0.6 [30 d sequential] and 1.1 kg ai ha(-1)) and hexazin one (1.1 kg ai ha(-1)) provided a 2-yr pooled TSA control of 97% at 120 d a fter treatment (DAT). Hexazinone applied at 0.6 kg ai ha(-1) provided varia ble TSA control averaging 100% in 1996 and 56% in 1997 (120 DAT). These dat a indicate that 97 to 100% TSA control can be obtained when herbicide treat ments are applied to regrowth 60 d following a heavy frost. Allowing frost to destroy photosynthetic tissue can replace mechanical mowing at a savings of $25 to $30 ha(-1).