Chemical weed control in oil-seed poppy (Papaver somniferum)

Field experiments were conducted in north-west Tasmania to assess the herbicides diquat and nitrofen, used singly and in combination, for selective post-emergence weed control in oil-seed poppies (Papaver somniferum). The species of weeds infesting the crop influenced yield responses to the herbicides. In the absence of fat hen (Chenopodium album) and fumitory (Fumaria muralis), crop production increased linearly with rate of diquat. The highest rate of diquat (280 g ha-1) produced a yield that was not significantly different (P = 0.05) from the hand-weeded control. In the presence of these two weeds, linear yield responses to rates of both diquat and nitrofen were obtained. There was no significant interaction effect on crop yields between these two herbicides, but a mixture of both chemicals was required for effective weed control. The tolerance of the crop to the herbicides was measured in the absence of weed competition. No effects on crop yields were obtained, although some treatments retarded the growth of the crop and caused a significant (P = 0.05) reduction in the height of the crop at flowering.