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Defoliants and Desiccants1
Frederick M. Fishel2This document discusses the meaning of the terms "defoliant and desiccant," their patterns of use, and provides a listing of these products registered for use in Florida.
Introduction: What are Defoliants and Desiccants?
Simply put, defoliants and desiccants are chemicals used to remove leaves from the plant - either from the crop itself, or from weeds in infested fields. In cotton production, leaf removal has several advantages:
- The crop may be harvested earlier;
- Quality grades are higher because of a lower content of leaf trash;
- Leaf removal facilitates air movement, and thus drier conditions which are favorable for boll-opening and less conducive to boll rot development;
- Harborage sites of insects that reduce lint quality are removed; and to some degree,
- Reduced lodging of the crop.
Defoliants
Plant defoliation does not hasten maturity; for maximum yield and crop quality potential, defoliants should not be applied until physiological maturity. Defoliants function in several primary ways, both resulting in more rapid development of abscission layers. The abscission layer is the zone where leaf petioles meet stems. Once adequately formed, leaves drop from the abscission layer. The older materials work by contact - rapid destruction of green tissue, which indirectly favors formation of abscission layers. Several other defoliants do not target green tissue destruction rather promote the formation of the abscission layer directly, resulting in leaf drop. The activity of a defoliant is favored by warm temperatures, particularly greater than 50°F.
FDACS Definition of "Defoliant"Any substance or mixture of substances intended for causing the leaves or foliage to drop from a plant, with or without causing abscission.
Desiccants
Desiccants are used for similar purposes as defoliants, but they function differently. Desiccants cause green foliage to lose water - a hastened drying process that results in leaf removal (generally faster than the result of a defoliant). Desiccants have several practical uses in production. They effectively destroy the crop following harvest, quickly eliminating pest harborage sites. Besides being a useful pest management tool, they can protect crop quality. For example, in potato production, the presence of massive green vine material can interfere with the harvest operation. Such interference can result in skinning and bruising of the tubers. Skinned and bruised tubers will readily discolor and are more easily predisposed to soft rot. Lower quality tubers lower fresh market value, and in some cases may be rejected entirely. Numerous materials that are applied for weed control are also registered for use as harvest aid chemicals. For example, paraquat and diquat dibromide are very fast-acting, are labeled for control of a wide spectrum of weeds, and have been used as effective harvest aids for many years. Legally, defoliants and desiccants are regulated as pesticides under the Florida Department of Agriculture and Consumer Services (FDACS) and must be registered for use as would any pesticide within the state.
FDACS Definition of "Desiccant"Any substance or mixture of substances intended for artificially accelerating the drying of plant tissues.
Table 1 lists commonly-used defoliant/desiccant materials that are registered for use in Florida along with some examples of trade names.
Additional Information
- Olson, S.M. and D.N. Maynard. Vegetable production guide for Florida 2002 - 2003, 7th ed. University of Florida IFAS/Extension.
Tables
Table 1. Materials registered for use as defoliants/desiccants in Florida with example trade names.
Active ingredient
Trade names
Diquat
Reglone®
Carfentrazone
Aim®
Dimethipin
Harvade®, Leafless®
Endothall
Accelerate®, Desicate®
Mepiquat chloride
Pix®
Sodium chlorate
Defol®
Pelargonic acid
Scythe®
Paraquat
Gramoxone®
Thiadiazuron
Dropp®, Ginstar®, Leafless®
Tribufos
Def®, Folex®
Footnotes
1. This document is PI-101, one of a series of the Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date February 2006. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. Frederick M. Fishel, associate professor, Agronomy Department, and Director, Pesticide Information Office; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.