Control of apple of Peru (Nicandra physalodes) in maize on the Atherton Tableland, Queensland

Abstract

On the Atherton Tableland, Queensland, apple of Peru (Nicandra physalodes) is a problem weed in maize. The competitive effects of N, physalodes, the effectiveness of various control measures and the residual life of atrazine (2-chloro-6-ethylamino-4-isopropylamino-I ,3,5-triazine) were investigated in three experiments each repeated over two seasons. In 1973 (a late season) populations of N. physalodes as low as 4.7 m-2 reduced yields by about 35 per cent and would have caused harvester impedance in a commercial situation. In 1973-74 (an early season) N. physalodes had less effect on yield but would still have impeded harvesting. In 1973 atrazine used pre-emergence at 2.24 kg a.i. ha-1 was sufficient for satisfactory weed control. During 1973-74 when weed growth was prolonged after crop ripening by wet weather a split application of atrazine applied at 1 .12 kg a.i, ha-1 pre-emergence followed six weeks later by a further 1.12 kg a.i. ha-1 was better in controlling weeds at harvest than the single pre-emergence application. Under the conditions of these experiments atrazine used at the above rates did not cause damage to oats planted immediately after the maize harvest.