Competition between cotton and velvetleaf and their tolerance to pyrithiobac-sodium as affected by silicon nutrition

Although silicon nutrition in crops has been reported to improve growth and herbicide tolerance, the response of crop-associated weeds has not been studied. To support or reject the hypothesis that silicon nutrition can affect the tolerance of velvetleaf to pyrithiobac-sodium, affecting crop-weed competition, this study was conducted as a dose-response study in which cotton and velvetleaf grown in soil with or without K₂SiO₃ + silicate-solubilizing bacteria (SSB) were sprayed with pyrithiobac-sodium. Some enzymes involved in lignin biosynthesis, antioxidant, and herbicide metabolism were measured to find physiological changes. The findings accept the hypothesis above for the first time. Silicon nutrition could disrupt pyrithiobac-sodium selectivity for controlling velvetleaf in cotton. Regardless of treatments, velvetleaf accumulated more silicon and lignin than cotton. Unlike phenylalanine ammonia-lyase, the activity of cytochrome P450 reductase (1.3 vs. 0.7 U/g), glutathione S-transferase (1.7 vs. 1.2 U/g), superoxide dismutase (21.7 vs. 12.5 U/mg), and catalase (443.9 vs. 342.5 U/mg) was higher in cotton than in velvetleaf, grown in soil without silicon nutrition. All enzymes became more active with silicon nutrition, but the increase was higher in velvetleaf. In field studies, velvetleaf benefited from silicon nutrition more than cotton, enhancing the competitive ability of velvetleaf in cotton and reducing further crop yield. K₂SiO₃ + SSB caused a 29.7 % increase in velvetleaf biomass, which caused the greatest damage to cotton seed (80.9 %) and lint (69.2 %) yields. It is recommended to avoid soil nutrition with K₂SiO₃ + SSB in velvetleaf-infested cotton fields, where velvetleaf control with pyrithiobac-sodium is intended.