Eliminates the need for synthetic pesticides .
Reduces transpiration without lowering crop output .
Chitosan is a natural plant elicitor because the exoskeletons of all insects are made of the same thing (chitin). When chitosan comes in contact with plants it “tricks” the plants into thinking they are being infested and the plant’s natural immune response is stimulated.
For many types of plants, this stimulating or eliciting of your plant’s immune response can increase the concentration and production of sap, resin, essential oils, fruit, and your plant’s overall size. It can also increase your plant’s resilience when being transplanted. It can even help revive stress-shocked saplings.
In solution, chitosan can be applied as a soil amendment, foliar spray, hydroponic amendment, or adjuvant. Chitosan not only provides an antimicrobial film that prevents mold growth , it causes a reaction that also improves the immune system of plants.
The similarity of chitosan to natural plant sugars encourages a bioactive effect that acts on the molecular level. When applied in soil, it has been shown that chitosan is able to stimulate beneficial microorganisms while inhibiting pathogens . When applied as a foliar spray, plant transpiration is reduced by stomata closure while also providing a barrier against mold, bacteria, and viruses.
In trials it has been show that “spraying tomato plants with chitosan increased all vegetative growth parameters expressed in plant height, number of branches, and number of leaves per plant in the first season and plant height in the second season…” 
 El Hadrami, Abdelbasset, et al. “Chitosan in plant protection.” Marine drugs 8.4 (2010): 968-987.
 Bautista-Baños, Silvia, et al. “Chitosan as a potential natural compound to control pre and postharvest diseases of horticultural commodities.” Crop Protection 25.2 (2006): 108-118.
 Bittelli, Marco, et al. “Reduction of transpiration through foliar application of chitosan.” Agricultural and Forest Meteorology 107.3 (2001): 167-175.
 Rabea, Entsar I., et al. “Chitosan as antimicrobial agent: applications and mode of action.” Biomacromolecules 4.6 (2003): 1457-1465.
 Barka, E. Ait, et al. “Chitosan improves development, and protects Vitis vinifera L. against Botrytis cinerea.” Plant Cell Reports 22.8 (2004): 608-614. E.M. El-Tantawy, et al. “Behavior of Tomato Plants as Affected by Spraying with Chitosan and Aminofort as Natural Stimulator Substances under Application of Soil Organic Amendments.” SciAlert