Topic: Chemistry
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Poly-D-Glucosamine (Chitosan) Crops
Chitosan (poly-D-glucosamine) is a polymer1 of glucosamine sugars, specifically glucosamine and N-acetyl- glucosamine (Hadwiger 2004). Its structure and composition are similar to both cellulose (i.e., the primary structural component of plant fiber) and chitin.
Like chitin, chitosan is found naturally in the shells of all crustaceans and insects, as well as certain other organisms such as many fungi, algae, and yeast. Chitosan is one of the most common polymers found in nature.
Chitosan is a chemically stable, white to pale yellow powder or flake (Polysciences 2003). Chitosan has a strong positive charge, which is the basis of its use as a "sticking" agent (i.e., an adhesive adjuvant). The positively charged molecules adhere to negatively charged pesticides and plant surfaces.
Chitosan is not soluble in water. It can be made soluble in water, however, by treating it with an acid to form soluble chitosan ions (Rabea et al. 2003). See Evaluation Question 1 form more information the production of chitosan.
Chitosan is a registered pesticide (OPP No. 128930) that is used in crop production as a plant growth enhancer and plant defense booster (EPA 2003). In these uses, chitosan is applied to treat field crops, ornamentals, turf, home gardens, and nurseries. Target pests include early and late blight, downy and powdery mildew, and gray mold. Proposed application rates for the petitioned use as a sticking agent are much lower than the application rates for use as a pesticide/fungicide. Chitosan is exempt from the requirement for a pesticide tolerance (EPA 1995). See Evaluation Question 6 for more information on chitosan application rates and Evaluation Question 8 for more information on the modes of action for approved legal uses as a biopesticide.
Source: www.ams.usda.gov
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