Dry heat and exposure time influence divine nightshade and itchgrass seed emergence

Authors: Spaunhorst, Douglas; ORGERON, ALBERT - Louisiana Cooperative Extension Service

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2019
Publication Date: 7/18/2019
Citation: Spaunhorst, D.J., Orgeron, A.J. 2019. Dry heat and exposure time influence divine nightshade and itchgrass seed emergence. Agronomy Journal. 3(5):2226-2231. https://doi.org/10.2134/agronj2019.02.0072.
DOI: https://doi.org/10.2134/agronj2019.02.0072

Interpretive Summary: In Louisiana, extra leaf material left on the soil surface is burned after harvesting sugarcane. Divine nightshade [Solanum nigrescens (Mart. & Gal)] and itchgrass [Rottboellia cochinchinensis (Lour.) Clayton] are problematic weeds in Louisiana sugarcane production. The objective of this study was to determine the effects of dry heat and exposure time on divine nightshade and itchgrass emergence by heating seeds in a laboratory oven for predetermined amounts of time. Seeds were exposed to three temperature levels (200, 300, and 400°F) for seven exposure timings (0, 5, 10, 20, 40, 80, and 160 seconds). A small portion of divine nightshade seeds emerged when exposed to 400°F for 160 s. However, itchgrass exposed to 300°F for 40 s or longer did not emerge. Exposure to 300°F for 5 to 20 s and 400°F for 5 to 10 s resulted in more than 100% divine nightshade emergence. It appeared that short periods of heat promoted seeds to germinate. Results from this study showed itchgrass seed could be controlled with dry heat, but temperatures below 200°F or temperatures greater than 300°F for short durations may not control all divine nightshade seeds. This research showed divine nightshade will become more abundant when low temperatures are produced, possibly when sugarcane residue is damp and or mixed with field soil, and shortly thereafter burned. The fluid-filled fruit that contained divine nightshade seed likely insulated the seed from exposure to extreme temperatures.

Technical Abstract: In Louisiana, growers remove sugarcane residue following green-cane harvesting by prescribed burning. Divine nightshade [Solanum nigrescens (Mart. & Gal)] and itchgrass [Rottboellia cochinchinensis (Lour.) Clayton] are problematic weeds in Louisiana sugarcane production. The objective of this study was to determine the effects of dry heat and exposure duration on divine nightshade and itchgrass emergence. Divine nightshade and itchgrass seeds were exposed to three temperature levels (100, 150, and 200°C) for seven exposure timings (0, 5, 10, 20, 40, 80, and 160 s). Divine nightshade emergence was not completely inhibited at 200°C for 160 s. However, itchgrass exposed to 150°C for 40 s or longer failed to emerge. Exposure to 150°C for 5 to 20 s and 200°C for 5 to 10 s resulted in more than 100% divine nightshade emergence, presumably short periods of heat exposure alleviated seed dormancy. Results from this study showed itchgrass seed could be controlled with dry heat, but prescribed burns that produced temperatures below 100°C or temperatures greater than 150°C for short durations may not control all divine nightshade seeds. The aforementioned temperature and exposure duration that allowed divine nightshade to survive, introduced the potential for divine nightshade to become more abundant. The fluid-filled fruit capsule that contained divine nightshade seed likely insulated the seed from being exposed to extreme temperatures.