Purpose
During the weeks of late fall & early winter, many landscapers apply their annual anti-desiccant sprays to broadleaf evergreen plants. Some of the common trade names of these liquid resin, spray-on products include Vapor-Guard, Wilt-Pruf, Stress Guard, and Nu-Film. Although plants go dormant during the winter, evergreens will continue to transpire given certain conditions. These applications help reduce excessive water loss from leaves during the dry winter months when the ground is frozen. An anti-transpirant is a film-forming complex of polyethylene’s and polyterpenes that when applied to foliage will reduce the moisture vapor transmission rate. Although much of the transpiration from leaves occur through small openings (stomates) under the leaves, a significant amount of water loss can also occur directly through the leaf cuticle or epidermis. The anti-transpirants function by increasing cuticle thickness of broadleaf evergreens.
This Rhododendron may have some winter injuries, but the primary cause for the plant decline is from wood borers. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Desiccated holly leaves (Winter Burn) with obvious symptoms. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Use of Anti-Transpirants
When 1 gallon of an anti-transpirant is applied to 10 to 20 gallons of water, plant moisture loss during the winter months is reduced between 15 to 20%. In addition, at the 5-10% dilution rate, the sprayed film produces a glossy sheen on broadleaf evergreens that is appealing to many clients during the holiday season. Some product labels state that a single application will last through the winter season, whereas other labels indicate a second application during mid-winter provides best results. Note that some of the most severe moisture loss from broadleaf evergreens typically occurs during late winter periods (e.g., February). Furthermore, the rate of transpiration will be greatest on plants growing in full sun on warmer, windy days. Hence, an anti-desiccant in place during this time and under these conditions will usually be most beneficial.
Aucuba foliage prior to spray of anti-transpirant. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Aucuba with glossy foliage after anti-transpirant spray. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
American holly foliage prior to anti-transpirant spray. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
American holly with glossy foliage after anti-transpirant spray. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
No Guarantees
The use of an anti-desiccant does not guarantee that foliage will be spared against winter “burn” type injuries. It should be remembered these treatments do not prevent, but only reduce moisture loss during the winter. Furthermore, anti-desiccants do not protect against plant cells being damaged from the formation of ice crystals within the foliage during excessively cold temperatures. Actually, tests indicate that anti-transpirants are most useful when the air temperature is above freezing, but the soils are still frozen or cold (water movement is extremely slow in soils or plant stems when temperatures are below 40°F.).
Anti-transpirant sprays will not protect foliage from excessively cold temperatures. (Photo Credit: Minuteman Landscaping)
Variegated Euonymus plants are highly prone to winter injuries & anti-transpirant sprays will be less effective. (Phot Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Precautions
As always, it is important to read the label included with all anti-transpirant products. Notice that some of these products are designed to be used only with broadleaf and needled evergreens and should not be applied to evergreens having scale-like leaf foliage (i.e., junipers, arborvitae, Cryptomeria, Chamaecyparis, & Leyland cypress). Using some anti-desiccants on scale leaf evergreens, for example, may encourage winter type injuries. In addition, when some anti-transpirants are sprayed late in the afternoon, they dry more slowly during the evening hours causing the film-ingredients to separate-out. This may cause a persistent white, frosty film to occur on the surface of broadleaf evergreens (e.g., Rhododendrons) appearing later in the winter that is not aesthetically pleasing. Sprayers should be washed out immediately after use with warm soapy water to reduce internal sprayer parts from becoming sticky and clogged with dried concentrate.
Plants having scale-like foliage (Chamaecyparis) can be injured by some anti-transpirant sprays. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Plants having scale-like foliage (Arborvitae) can be injured by some anti-transpirant sprays. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Although the waxy, film-forming products do reduce leaf moisture loss, they also reduce the amount of carbon dioxide allowed to pass through the leaf stomate pores. Evergreen plants do continue to photosynthesize even during the winter months. The reduction of a sufficient level of carbohydrates can cause a reduction in energy for the normal growth of leaves, stems, roots, and flowers. Therefore, closing the pores of evergreens to protect them from winter sun & wind can be a benefit, but it could also result in a weaker plant being more susceptible to other stresses. These could include drought, insects & diseases.
Final Statements
Generally, anti-transpirants are tools to help plants growing in otherwise optimal conditions to endure stressful, short-term conditions. These products seem worth it for prized specimen plants , but probably not for routine use in the landscape. It is important to remember that these applications are not likely to be successful as stand-alone winter protections. Standard horticultural approaches such as watering dry soils before the ground freezes and proper mulching practices will increase the efficacy of any anti-transpirant application. Finally, sometimes the use of the unsightly burlap barrier may be the best remedy to protect plants in more extreme environmental sites. Although these hideous looking winter protections are a last resort, they will also provide the best barrier from sprays of de-icing salts on roads or driveways.
Although unattractive, burlap covering will give the best protection from winter damage. (Photo Credit: Missouri Botanical Gardens)
Proper mulching practices will increase the efficacy of anti-transpirant applications. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Reference: Plant & Pest Advisory (Vol. 9, No. 16); “Anti-Transpirants-Winter Sprays to Protect Broadleaf Evergreens,” (by RCE Ag. Agents N. Polanin, W. Hlubik, R. Obal, P. Nitzsche) & Reference: Plant & Pest Advisory (Vol. 16, No. 16); “When Not to Use Anti-Transpirants,” (by RCE Ag. Agent Claire Liptak)
