Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Antitranspirants and antidesiccants are materials applied to plants to limit water loss. They have been used with some success in horticulture, especially in the ornamental industry. I was recently asked if they could be used to improve transplant survivability for vegetable crops. Research has shown some benefits, but results have been inconsistent.
Transplants most commonly desiccate when water loss exceeds water uptake. This commonly occurs in transplants because root systems are small, limiting uptake, and water loss in windy conditions or on hot days is high.
Remember that most water moves out of plants through regulated pores in the leaves called stomates. This is called transpiration. These openings have specialized cells that can open and close, depending on environmental conditions and plant internal signals. Controlling stomates and transpiration can reduce water loss and plant wilting.
Leaves also have waxy cuticles that limit non-stomatal water losses. However, in plants that have thin cuticles, in new leaves where cuticles are still forming, and under extreme drying conditions, such as high winds, water loss through the cuticle can be significant.
Antitranspirants/antidesiccants work in one of 5 ways:
1. Chemicals such as hexaoctadecanol, cetyl-alcohol and steryl-alcohol reduce transpiration by entering the leaf and forming a barrier from within to reduce transpiration loss of water.
2. Chemicals that are metabolic inhibitors such as PMA and DSA prevent stomatal opening.
3. The plant hormone abscisic acid (ABA) causes stomatal closure.
4. Wax and oil emulsions or chemical film materials such as di-1-p-Menthene prevent water loss by completely covering the leaf surface with a film. This limits losses through the epidermis and by covering part of the stomatal opening.
5. Reflective antitranspirants, most commoly clay based, reflect light energy thus reducing leaf heating and water losses. This is most useful for later plantings under heat load. It does not have much impact on wind desiccation.
Not all of these materials are registered for food crops so you need to read the label before using them on vegetables. The most commonly used with vegetables have been film coverings and reflective materials.
In addition to these materials, gels have been used to protect transplant roots. Transplants are dipped in the gels prior to planting and this can reduce root loss due to drying and thus improve the ability of transplant roots to survive, grow, and take up water.
In a 4 year trial with cantaloupes, researchers in Nebraska evaluated the effects of an antitranspirant (Folicote) sprayed on plants and a polyacrylamide gel root dip (SuperSorb) on early growth of transplanted muskmelon with or without windbreak protection. They found that “overall transplanting success and early growth were enhanced the most by wind protection, followed by the polyacrylamide gel root dip, and least by the antitranspirant foliar spray”.
Currently research is underway looking at the plant growth regulator ABA for height control of transplants and to improve early season survivability. It is being trialed in crops such as tomato and watermelon in several states. ABA is the plant hormone that controls stomates. Results have been encouraging and it may be labeled for this use in the future.
My base recommendation is that for maximum transplant survival you should produce compact, well hardened off transplants and provide wind protection at transplanting. Antitranspirants and antidesiccants are additional tools that can marginally improve transplant success.