Please stop making and applying homemade soap sprays to control pests.
For years I have been trying to convince home gardeners not to make and use homemade pesticides in particular sprays made from dish soap for insect control. A common response to my warning is, “It’s just Dawn dish soap, I use it on dishes I eat off of plus they use it on wildlife after oils spills, so it has to be safe for our plants.” These home gardeners refuse to believe the science based information I provide and instead choose to follow unscientific, unsearched claims they found on the Internet and in garden articles about making and using homemade soap sprays.
Homemade dish soap sprays might kill insects if you are lucky enough mix it so you get the appropriate concentration in the final product to be sprayed. There are probably more than a million different recipes on how to make homemade soap sprays at home. The recommended dilution rates vary tremendously from one recipe to the next. And they do not take into consideration the concentration or ingredients in the soap to be used. The result is that concentration of your homemade spray will likely not be diluted properly and therefore it little chance at being effective in killing insects.
As a certified IPM Advocate for 9 years I spent a lot of time working at numerous retail nurseries. When gardeners would come into the nursery and ask me for a pesticide to control soft-bodied insects such as aphids I would recommend a proven, highly effective and university endorsed product sold at the nursery, insecticidal soap. The majority of gardeners told me that insecticidal soap does not work. They need something stronger. I always inquired if they made and used a homemade soap spray and every time the answer was yes, they made it themselves. Because their improperly manufactured homemade concoction used inferior and toxic ingredients of course it did not work. From their experience they assumed that store bought insecticidal soap also would not work. This was an incorrect assumption. Rarely could I convince them there was a quality and concentration problem with the spray they made and that if they used the store bought version it would be very effective. Instead they would purchase a much more toxic product that did more damage to the environment, beneficial organisms, and themselves and their family.
The article "Dish Soap Can Damage Your Plants" referenced two university publications that recommend that homemade soap sprays should not be used for pest management. This lead me to several other university publications that also cautioned people to not make and use homemade soap sprays to kill insects for a variety of reasons.
What I hope will discourage home gardeners from making and using their own homemade soap insect sprays is university research repeatedly indicated that HOMEMADE SOAP SPRAY ARE DAMAGING TO YOUR PLANTS!
Need an explanation… Think about it, dish soap effectively removes oil, grease, and wax from your dirty dishes. So it only follows that when you spray your homemade soap solution on your plants it would also remove the natural oils and waxes that your plants have coating their leaves (you didn’t know the leaves were coated with natural oils and waxes did you). These natural coatings are vital to protect the leaves from pests and environmental stresses. Your homemade soap spray removes these protective barriers making it easier for diseases to attack and get a foothold on your plants foliage. Your action sets your plant up to get attacked, decline in health and possibly die. If that wasn’t enough the ingredients in your homemade brew are often damaging to plant leaves. You may not see visible damage, but the plant is weakened and without its protective coating making your plants much more susceptible and attractive to pest attack.
These university reports explain how commercial insecticidal soap is very different from homemade dish soap spray and why the later is not designed for pest management and can cause plant damage. When you use a pesticide you should always read and follow label directions. Do your dish soaps have instructions on how to dilute and apply them for pest management – NO!
The University of Connecticut’s UCon Home & Garden Education Center states, “Dishwashing soaps and detergents are designed to remove grease from dishes and may cause plant damage by dissolving the waxy cuticle on plant leaf surfaces. There is increased risk of plant injury with the use of dishwashing soaps and detergents (not labeled as a pesticide) when used as a spray.”
Clemson University’s Cooperative Extension Home & Garden Information Center explains that there is a difference between commercial insecticidal soap and your ordinary dish soap. “Commercial insecticidal soaps are a highly refined version of liquid dish soap. While you could make your own insecticidal soap mixture, there is a substantially increased risk of plant injury with them. Dry dish detergent and all clothes-washing detergents are far too harsh to use on plants because of all the additives in them. Some soaps and detergents are poor insecticides, and other additives in these products may be Phytotoxic (i.e., damage the plant.).”
The University of Florida IFAS Extension’s article “Managing Plant Pests with Soaps" states, “Most dish soap products are not true soaps, but powerful surfactants called detergents. These products consist of synthetically produced detergents and other chemicals designed to strip grease and oily residue off cookware and other surfaces. These soaps work extremely well for cleaning and sanitation purposes. Directions for proper use can be found on a product label and the safety data sheet (SDS). If the company does not include uses on garden plants or as a pesticide then the product should not and may not be used as such. Dish detergents (e.g., Dawn®, Joy ®, Palmolive®) are not an organic alternative to pesticides and are not appropriate for pest control in organic or conventional gardening. They also frequently contain antimicrobial ingredients and can severely disrupt microorganisms (including beneficial insect-parasitic fungi) contacted by the detergent. The powerful oil-stripping properties of detergents and concentrated soaps are believed to severely disrupt the delicate layer of wax on the surfaces of plant leaves and fruits. Similar in function to our skin, a plant’s waxy cuticle is the primary mechanical defense against microbial, viral, and fungal invasion. The waxy cuticle also acts as a barrier against water and solute loss. If a plant loses this protective layer, it will lose more water by transpiration, and its foliage will dry out. Plants adapted to drought, low humidity, and strong sunlight (such as succulents) typically have a much thicker waxy cuticle layer to help protect against water loss and may be more susceptible than other types of plants to detergent damage.” This means homemade soap spray are particularly damaging to plants during dry spells (such as Sacramento’s dry summer climate). In particular your homebrew is more damaging to our expanding and appropriate use of water-wise/drought tolerant plants.
The article from Florida also discusses the concentration issue when using homemade soap sprays as well as contaminants the products contain that the home gardener does not even consider. “Inconsistency in the application rate, or amount of soap per volume of water, causes many of the problems associated with using dish detergents and other soap products as pesticides. Recipes from gardening websites or homemade mixes can vary widely, from 1 tsp/quart to ¼ cup/quart, and often include other potentially phytotoxic ingredients, such as vinegar and alcohols. These recipes fail to consider the type of soap and safe application rates, environmental cautions, target pest type, and sensitivity of the plants.”
Iowa State University Extension and Outreach in their article, “Control Houseplant Insect Pests Safely With Insecticidal Soap” states, “They aren’t simple detergents anymore to cut grease and grime, they now contain air fresheners, “power scrubbers,” anti-bacterial agents, fragrances, lotions and other ingredients. Most detergents also contain surfactants to reduce the surface tension of water and make it “wetter.” These added products may be phytotoxic to sensitive plants and cause their leaves to be deformed or discolored, or even die back.” “It is probably easier and less risky to purchase the convenient, effective and dependable commercial insecticidal soaps available at most garden centers.”
The University of Florida article compares commercial insecticidal soap sprays with your homemade concoctions stating of the home brews, “They are often not as effective and pose greater risk of injury to the plant and environment.” Their article goes on to say that “Because detergents and other household soaps are neither designed nor labeled for use on plants or as pest control products, their use as a makeshift pesticide is not recommended.”
PLEASE STOP MAKING AND USING HOMEMADE SOAP SPRAYS TO KILL INSECTS AND MITES. I have provided you some factual information about homemade soap sprays and how damaging they can be to not only the environment but also the plants you are trying to care for. It is not just soap after all and it does not have pesticide recommendations on the label.