Wednesday, August 17, 2016

Soap destroys plants' defenses

How to fight aphids on milkweed?

We plant milkweeds to encourage the monarch butterflies, not only for the nectar, but also because milkweed is the ONLY larval food for the monarch caterpillars. But milkweed also attracts aphids...
Non-native scarlet milkweed (Asclepias curassavica)*. Notice all the yellow aphids on the stems.
I was focused on the monarch when I took the above photo, but it's obvious that my milkweeds had become infested with aphids. I just allowed the aphids to stay. Eventually some ladybugs came in, but the plant is better off without any "treatment" from the gardener.

Often the "expert" advice is to spray homemade concoctions with soap or detergent to get rid of the aphids. Don't do it!