# Natural Salicylaldehyde for Fungal and Pre- and Post-Emergent Weed Control
## 3 Results and Discussion  
Agricultural Byproducts (Walnut Shell Particles) as SA Delivery Vehicles: Intrinsic Antifungal Activity of SA as a Fumigant  
Initially, walnut shell particles were investigated as sustainable delivery vehicles for SA. Since nutshells are commonly contaminated with environmental microbial pathogens (Figure S1b), caution should be exercised during the recycling of tree nut byproducts. For the optimization of SA delivery, SA was tested as a fumigat at 1.2 M to target the aflatoxin-producing _A. flavus_ 3357. As shown in Figure 1, SA at 1.2 M, emitted from the delivery vehicles, completely prevented the growth of _A. flavus_ 3357 on the culture plate, while none of the nutshell particles showed an indication of microbial contamination on the surface. It can be concluded that walnut shell particles could serve as safe, effective delivery vehicles for emission of SA, which possesses an intrinsic antifungal activity. Tree nutshells (e.g., almond, hazelnut, pistachio, walnut shells) have been investigated extensively for use in various industrial processes/practices. While tree nut biomass, such as walnut shells, has been converted to solid biofuel through torrefaction [23], tree nutshells have also been tested as economic biosorbents, such as: (1) toxic heavy metal removal from contaminated waters by nutshells [24], (2) rhodamine B cationic dye elimination from contaminated aqueous solutions with acrylic-acid-modified walnut shells [25], (3) amine-functionalized walnut shells as a novel adsorbent for the removal of the pollutants PO4\({}^{3-}\) and NO3\({}^{-}\); the mechanism of the adsorption was determined as electrostatic interactions and hydrogen bonding [26]. Although walnut shell-derived cellulose nanocrystals possess the potential as effective nanocarriers in the food and drug delivery industries [27], studies exploring the use of walnut shells as drug/chemical delivery vehicles are currently very scarce. Overcoming Fluidoxovil Tolerance of Mitogen-Activated Protein Kinase (MAPK) Mutants of Aspergillus fumigatus (sakAA, mpkCA) or Penticillium expansum (FR2, FR3) by SA  
Chemo-sensitization was previously developed as a new antifungal formulation strategy, whereby co-application of a second compound (chemo-sensitizer; natural or synthetic) with a commercial antifungal agent (fungicides, drugs), both at sub-inhibitory concentrations, greatly enhances antifungal efficacy of the treatment [28]. A chemo-sensitizer causes the target fungi to become more susceptible to the treatment by modulating the pathogen's defense system, such as antioxidant or cell wall integrity systems, to the agents. Therefore, chemo-sensitization could contribute to the development of a new antifungal formulation, wherein the chemo-sensitizers serve as potent \"adjuvants\" enhancing the antifungal efficacy of commercial fungicides or drugs co-applied. The potential of SA as a chemo-sensitizer was investigated to overcome the fluidoxovil (phenylpyrrole fungicide) tolerance of _A. fumigatus_ and _P. expansum_. Fluidoxovil was chosen as a model fungicide for SA chemo-sensitization because its current application to the tree nut orchards has increased public concern over the toxicity fluidoxovil may trigger in humans and non-target organisms, including aquatic organisms [29; 30]. Therefore, the chemo-sensitization capacity of SA to fluidoxovil will enhance the antifungal efficacy of the treatment, lowering the doses of the fungicide required for the effective control of fungal pathogens. The fungicidal effect of fluidoxovil is exerted via the fungal osmotic/oxidative stress signaling system, namely, the mitogen-activated protein kinase (MAPK) pathway [31]. Fluidoxovil disrupts fungal growth by triggering unusual, excessive stimulation of the osmotic/oxidative stress signaling MAPK system, thus causing energy drain [31]. This MAPK pathway is responsive to osmotic/oxidative cues and, hence, protects the wild-type fungal cells from environmental osmotic/oxidative stressors.