Burning post-harvest sugarcane residue for control of surface-deposited divine nightshade (Solanum nigrescens) and itchgrass (Rottboellia cochinchinensis) seed

Authors: Spaunhorst, Douglas; ORGERON, ALBERT - LSU Agcenter; White, Paul

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2019
Publication Date: 8/7/2019
Citation: Spaunhorst, D.J., Orgeron, A.J., White Jr, P.M. 2019. Burning post-harvest sugarcane residue for control of surface-deposited divine nightshade (Solanum nigrescens) and itchgrass (Rottboellia cochinchinensis) seed. Weed Technology. 33(5):693-700. https://doi.org/10.1017/wet.2019.65.
DOI: https://doi.org/10.1017/wet.2019.65

Interpretive Summary: In Louisiana, burning post-harvest sugarcane residue is a standard practice to remove leaf material after harvesting and before spring regrowth occurs. Live-fires were simulated from field-collected post-harvest sugarcane residue and seeds of divine nightshade and itchgrass were exposed to dry and moistened post-harvest residue (PHR) at four densities (2.7, 5.4, 8.2, and 10.9 ton ac-1) and a nonburned control. The moisture content of residue exposed to simulated rainfall was 14% more in run two than run one; however, PHR with 44% moisture when wind speeds were lower allowed the fire to continue and created a smoldering effect which reduced weed emergence by 23% when compared to burning PHR with 30% moisture during breezy conditions. The moist 2.7 ton ac-1 PHR treatment resulted in 53% more divine nightshade and itchgrass emergence when compared to 2.7 ton ac-1 of dry PHR after burning and greater emergence was caused by more divine nightshade seed survival than itchgrass. Dry and moistened PHR failed to influence the burn duration; however, the burn duration increased 103 and 56% as the amount of PHR increased from 2.7 to 5.4 ton ac-1 and 5.4 to 8.2 ton ac-1, respectively. The combination of high wind speeds plus moist PHR did not increase the maximum burn temperature near the soil surface, but surface deposited divine nightshade and itchgrass seeds were sensitive to long exposure times at 212 °F. Burning PHR from fields that have poor stands or older stubble, especially when PHR is very wet or when water ponds in the wheel furrows, will not produce temperatures hot enough to kill divine nightshade and itchgrass seeds. The fluid-filled and fleshy content that makes up divine nightshade fruit, protected seed from short periods of high temperatures, but the fluid-filled berry may not protect seeds long enough when exposed to a smoldering fire.

Technical Abstract: Burning post-harvest sugarcane (Saccharum spp. hybrids) residue is a standard practice to remove extraneous leaf material before spring regrowth. Live-fires were simulated from field-collected post-harvest S. hybrids residue and seeds of divine nightshade (Solanum nigrescens) and itchgrass [Rottboellia cochinchinensis (Lour.) Clayton] were exposed to dry and moistened post-harvest residue (PHR) at four densities (6.1, 12.1, 18.2, and 24.2 Mg ha-1) and a nonburned control. The moisture content of residue exposed to simulated rainfall was 14% more in experiment two than experiment one; however, burning PHR with 44% moisture when wind speeds were lower allowed the fire to continue and created a smoldering effect which reduced weed emergence by 23% when compared to burning PHR with 30% moisture during breezy conditions. The moistened 6.1 Mg ha-1 PHR treatment resulted in 53% more S. nigrescens and R. cochinchinensis emergence when compared to dry 6.1 Mg ha-1 PHR after burning and greater emergence was attributed to more S. nigrescens seed survival than R. cochinchinensis. The PHR condition failed to influence the burn duration; however, the burn duration increased 103 and 56% as the amount of PHR increased from 6.1 to 12.1 Mg ha-1 and 12.1 to 18.2 Mg ha-1, respectively. The combination of high wind speeds and moistened PHR did not enhance the maximum burn temperature near the soil surface, but surface deposited S. nigrescens and R. cochinchinensis seeds were susceptible to prolonged exposure times at 100 C. Burning PHR from fields with poor stands or older ratoon, especially when PHR is abundantly wet or when water ponds in the wheel furrow, will not produce temperatures lethal to S. nigrescens and R. cochinchinensis seeds. The fluid-filled and fleshy content that comprises S. nigrescens fruit protected seed from short durations of high temperatures, but may not insulate seeds long enough when exposed to a smoldering fire.