As a member of the GWA (Garden Writers Association), I routinely get emails about new garden products. Here’s one I received this week:
“I thought your readers or listeners might be interested in learning of a new way to protect their plants without using pesticides. Moisturin, which contains no toxic ingredients, is sprayed on plants to form a clear flexible barrier strong enough to lock out both insects and airborne plant disease. Moisturin is inexpensive, easy to use and extremely effective. I would like to send you some at no charge for your own trial. If your satisfied with it performance I hope you will pass it s benefits onto the people who trust your opinion.”
It turns out that Moisturin is simply a repackaged antitranspirant. Briefly, these spray-on barriers prevent water loss physically (by covering stomata) or physiologically (by closing stomata). Interfering with stomatal function both reduces carbon dioxide uptake and water movement within the plant. You can read more about antitranspirants here.
But do antitranspirants have an effect on diseases or insects? Research indicates that while antitranspirants may reduce insect attack, their efficacy against diseases is less clear. They also show a clear negative impact on the plants they supposedly protect, to the extent they’ve even been tested as a form of weed control.
The best way to reduce pest and disease problems in garden and landscape plants is to keep them healthy. Reducing their ability to function normally by clogging their stomata will do exactly the opposite.