## 4 Limitations of Using Plant Products as Bioherbicides
### Solution Stability and Soil Biodegradability of Nepetalactone and Phloretin  
The long-term stability of specialized metabolites with practical applications, such as bioherbicides, is of crucial importance. The stability of NL in soil has not yet been tested and will be the focus of our future research. [PERSON] et al. [258], however, indicate the stability of _cis.trans_-NL, _trans.cis_-NL, nepetalic acid (NA), and dihydrometgalactone (DHNL) in dry plant samples (using ethanol as a solvent and calculated as % of compound per dry weight of plant samples, _w:w_), in dry extracts after the evaporation of ethanol (calculated as % of compound per dry weight of extract, _w:w_), and in extracts dissolved in ethanol (calculated as mg of compound per mL of ethanol, _w:v_) of _N. cataria_ stored under ambient light or in darkness. Using UHPLC-QTOF/MS or UHPLC-QQQ/MS, the concentrations of the compounds were analyzed over two years to determine the best storage methods, although a one-year study is required for pharmaceutical products according to the Food and Drug Administration (FDA) [259]. These results are important for possible commercialization and for establishing storage conditions that help maintain the efficacy of bioherbicides whose active ingredient is NL. _Cis.trans_-NL in dry plant samples of _N. cataria_ was degraded faster compared to _trans,cis_-NL. When exposed to light, the total amount of NL decreased by 98% after two years. When the samples were protected from light, the total NL content was ten times higher than in the light-exposed group. In both treatments, the content of _cis,trans_-NL decreased to almost zero after only two months. _Trans,cis_-NL in the extract was degraded more slowly than _cis,trans_-NL. After 16 months, the samples stored in darkness contained 6.76% _trans,cis_-NL, which was six times higher than in the samples exposed to light. During long-term storage of extracts with a high _trans,cis_-NL content, light protection significantly increases stability. In samples with ethanol solution, _cis,trans_-NL degraded faster than _trans,cis_-NL, although the degradation was slower than in the extracts. In both light-exposed samples and samples stored in darkness, the amount of _cis,trans_-NL reached zero after 16 months. The trend of constant _trans,cis_-NL concentrations occurred in the samples with ethanol solution, and the concentration remained at approximately 7 mg mL\({}^{-1}\) throughout the 24-month experiment in darkness. The DNL content remained stable over the two years, whereas the NA content increased from 1.046 to 1.926% in the extract samples stored in the darkness and to 1.744% in the light-exposed samples. NA concentrations were increased in both groups, which could be due to the hydrolysis of NL [258]. A high water content has been shown to significantly accelerate the degradation of various bioactive compounds in extracts, solutions, or emulsions of EOs, while ethanol solutions of extracts have been shown to be more effective in minimizing the degradation of iridoids [258]. In addition, crude plant extracts often require encapsulation or other advanced formulations to preserve their stability. Currently, there is a lack of sufficient data regarding the persistence of dihydrochalcones in the soil, which limits our understanding of their behavior and stability in soil environments. [PERSON] et al. [260] provided the first evidence of the low soil persistence of dihydrochalcone, isoflavue, and aliphatic phenol. The dissipation of dihydrochalcone was between 1.20 to 10.23 days in three different soil types (Dijon, France; Prufbericht, Germany; and commercially available soil from LUFA Speyer, Speyer, Germany) [260]. The obtained results also indicated a slower dissipation of these three plant-derived compounds in the Prufbericht soil compared to the other two soils.