Insecticidal soap

Managing our gardens is very important in order to keep diseases under control as well as insects. This summer, while many of us did quite well with our vegetable gardens and our perennial gardens, we did see a higher than usual number of certain insects in our gardens.

As we all become more familiar with the need to protect pollinator insects, we have recognized that insecticides will kill all insects, good or bad. We are all learning that indiscriminate spraying of pesticides will also kill bees and other insects that we want to keep. This has brought many of us to rethink pesticides in our gardens and so there are many discussions about insecticidal soap.

Insecticidal soap will work to deter many soft-bodied insects such as aphids and it could even work to some degree on beetles. It works by washing off a protective coating that is on these insects, which causes them to dry out and die. There isn’t a whole lot of information yet on if or how it works on other insects such as bees so it is still in our best interest to use it with caution around pollinating insects.

Insecticidal soap can be easily made at home. It is usually a 2% solution, which can be made by measuring 2 teaspoons of soap of your choice into one pint of water. Gardeners can also purchase insecticidal soap, ready to use (RTU) on the store shelf. This works just as well as the homemade sprays. Caution, with any kind of spray, is always needed no matter what we are using in the garden. Following the instructions is the law for any kind of spray that we use and is necessary in order to keep from damaging our plants in the garden setting.

Soft-bodied insects include aphids, thrips, mites and whiteflies. The tougher insects such as caterpillars and beetles (which include Japanese beetles) will generally not be harmed by insecticidal soap. The other draw back to insecticidal soaps is that often these soft-bodied insects live underneath the leaves of the plants. This means, actually turning the leaves over (or holding the plant upside down if it is in a pot) and then spraying will give you the most bang for your buck. The insect must be thoroughly sprayed in order for insecticidal soap to work.

Some plants are sensitive to insecticidal soap as well. Tomatoes, plums, cherry and a few others can be easily burned by the insecticidal soap. In addition, like most other sprays, we cannot use it on very hot days (anything over 90 degrees F) or on plants that are stressed whether it might be from drought or disease/insect problems. It is always best to catch problems early and take care of them as soon as you are able in order to use the least amount of pesticide whether it is an insecticidal soap or some other ready to use product for perennials or vegetable gardening. Generally speaking, leaf burn is an issue and is compounded by using sprays on very hot days of the summer.

Insecticidal soaps also work well for houseplants and I recommend that houseplants that have been outdoors be inspected closely for any riders coming in from outside but especially aphids. For smaller plants, it might be worth your effort if you find aphids on your houseplants to spray them and then place them in a bag such as a dry cleaning bag, for about a week to make sure that no insects escape and it seems to make the spray more effective for the plants. For more information, visit https://extension.umn.edu/yard-and-garden-news/coming-clean-soap-garden

For more information on gardening, you can reach me at s.dejaeghere@me.com


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