## 4 Limitations of Using Plant Products as Bioherbicides
### Effect of Nepetalactone and Phloretin on Non-Target Organisms
#### 4.3.2 Effects on Soil Microbiota
These studies, which present conflicting results, indicate that if EOs, extracts, and water emulsions are to be used in the field for integrated weed management, further research is needed to clarify their impact on soil microorganisms. Therefore, optimizing doses and treatment methods is essential to minimize harmful effects while maintaining weed control efficiency. Sustainable strategies for using bioherbicides are key to ensuring long-term soil health. [PERSON] et al. [260] conducted q-PCR analysis to determine the potential effect of the dihydrohalcone applied at an agronomic dose rate of (\(\times\)1; 0.6 \(\mathrm{\SIUnitSymbolMicro g}\)/g soil) and (\(\times\)10; 6 \(\mathrm{\SIUnitSymbolMicro g}\)/g soil) on the abundance of broad taxonomic groups, such as total bacteria and fungi, in three different soil types (Dijon, France; Prufbericht, Germany; and commercially available soil from LUFA Speyer, Germany). The authors demonstrated that dihydrohalcone induced a significant dose-dependent decrease in the abundance of total bacteria in the Djon soil 28 days after application, an effect that was not replicated in the other two types of soil. In contrast, fungal populations were unaffected in all of the tested soils. The authors further extended their analysis to ammonia-oxidizing microorganisms (AOMs), which are important for the nitrogen cycle. AOMs include ammonia-oxidizing archaea (AOA; _Nitrososphaerales_ and _Nitrosotaleales_) and ammonia-oxidizing bacteria (AOB; _Nitrosospira_, _Nitrosomonas_, and _Nitrosococcus_). They concluded that dihydrohalcone significantly changed the percentage difference in AOA (\(-\)58.9 to 208.5%) and AOB (\(-\)48.5 to 57.2%) depending on the soil type. Considering that phloretin and phloretin are the main components of apple exudates [31] and were linked to ARD in previous studies [236, 264], data on the influence of ARD-affected soil could be valuable in evaluating the impact of phloretin on soil microbiota. ARD-affected soil causes changes in the soil microbiome due to complex interactions between living organisms, external factors, and soil properties [297, 314]. It is evident that ARD alters the microflora to the detriment of beneficial organisms, resulting in the proliferation of microorganisms that impair apple tree growth, such as the oomycetes _Pythium_ and _Phytophthora_, the fungi _Cylindrocarpon_ and _Rhizoctonia_, Actinomycetes, and bacteria such as _Bacillus_ and _Pseudomonas_[315, 316, 317]. Genetic sequencing of ARD soil samples showed that eukaryotes accounted for only 1.96% (\(\pm\)0.2) of the total reads, the majority of which were classified as fungi (58.7% \(\pm\) 2.27), while archaea and viruses accounted for less than 0.55 and 0.07% of the total reads, respectively. Bacteria from the phyla Proteobacteria, Actinobacteria, Bacteroidetes, and Acidobacteria were the most abundant in the rhizosphere metagenomes [318]. In ARD-affected soils, the genera _Friedmanniella_, _Terrabacter_, and _Thermoophilium_ were the most reduced compared to uncontaminated soils. Additionally, a reduced number of reads were found for the genera _Mycobacterium_, _Pedosphaera_, and _Solirubrobacter_. In contrast, the genera _Optitus_, _Dongia_, and _Novosphingobium_ were more frequently represented in the soil samples affected by ARD. The genomic sequencing results of ARD soil samples in Italy indicatedthat ARD soils were dominated by the phyla Proteobacteria, Actinobacteria, Acidobacteria, and Bacteroidetes, which accounted for 24 and 71% of all sequences, respectively [319]. In conclusion, there is a potential for phloretin to influence changes in the soil microbiome, which may have significant implications for soil health and plant growth. However, further research is necessary to fully understand the direct effects of phloretin applied at different concentrations. These studies should focus on the impact of phloretin on soil microbial communities, their functional roles, and the broader ecological implications.