Critical period for weed control in flue-cured tobacco
Field experiments were conducted to determine the critical period for weed control (CPWC) in flue-cured tobacco. This period consists of two separately measured timings; a critical weed-free period and a critical timing for the weed removal period. Treatments consisted of weed removal at 2, 4, 6, 8, and 10 weeks after planting (WAP) and weed-free periods of 2, 4, 6, 8, and 10 WAP. In addition, a season long weedy and season long weed-free treatment were included. The crop was subjected to standard management practices; aside from herbicides and cultivation. The experimental design was a randomized complete block design with four replications. Results showed that the critical timing of removal was 4.4 weeks after transplanting (WAT) and the critical weed free period was 6.8 WAT; therefore, the critical period of weed control in flue-cured tobacco was between 4.4 and 6.8 WAT in mixed populations of both grass and broadleaf weed species. No difference in yield was observed when flue-cured tobacco was kept weed-free for the first 6 WAT or when weeds were removed at 6 WAT and kept clean for the remainder of the season. Yields for treatments where weeds were not removed until 8 and 10 WAT were similar to the season-long weedy treatment. Trends with crop value and quality are consistent with trends associated with yield. In general, trends with total alkaloids and reducing sugars were similar to that of yield; the higher the yield, the higher the nicotine content with lower reducing sugars. The lower the yield, the lower the nicotine and higher reducing sugars. This is expected as treatments with lower yield were subjected to greater weed competition; potentially reducing light and nutrient availability to the tobacco plant.