Using a neem oil soil drench to prevent aphid infection on a crepe myrtle tree - Ask Extension
Hello!
I have been reading on my gardening sites online about using a soil drench to prevent infestations of aphids. The drench is 1 gallon of wat...
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Using a neem oil soil drench to prevent aphid infection on a crepe myrtle tree #786590
Asked April 12, 2022, 2:07 PM EDT
Hello!
I have been reading on my gardening sites online about using a soil drench to prevent infestations of aphids. The drench is 1 gallon of water, 1 tsp of dawn or Castile soap, and 2 Tbsp of 100% cold pressed Neem oil which apparently contains more of the active ingredient azadirachtin. Apparently it becomes a systemic insecticide that is effective against insects who penetrate the plant (like aphids on the undersides of leaves). I just want to be sure that 1. This won’t harm beneficial insects, and 2. That the ratio of oil in the drench won’t hurt the roots of the tree, and 3. If you all think this is actually an effective strategy.
Last year I had a terrible infection on a new crepe myrtle we planted in early March. By June it was totally ingestion and developed sooty mold. Foliar Neem oil sprays killed the aphids but the damage was done. Trying to prevent similar occurence this year.
Your advice is much appreciated!
Claire Duncan
Austin, TX
Travis County Texas
Expert Response
Claire,
We cannot endorse any specific recipes or treatments. However, we can provide suggestions for your consideration.
I would recommend monitoring the crepe myrtle, since the severity of aphid infestations can vary from year to year. If control is necessary, try one of the least toxic methods outlined in the attached Grow Green fact sheet. Often, spraying the crepe myrtle with water at high-pressure from a garden hose will work. Also, beneficial insects, like lady beetles, help keep aphids under control.
If you notice the aphid population increasing, you may want to try one of the non-systemic solutions mentioned. Horticultural oils, although generally considered safe, can sometimes cause damage. When treating a new plant, apply to a small area first to see if there is any adverse reaction. As summer approaches, consider recommended temperature ranges for application. Be sure to follow all directions on the label.
You are correct. Azadirachtin used in a soil drench, will be taken up by the crepe myrtle making its foliage toxic to any foliage-feeding insects, not just aphids. There is no guaranteed that beneficial insects will not be harmed.
https://agrilifeextension.tamu.edu/library/landscaping/aphids-in-texas-landscapes/
has more information on aphids, including their life cycle and management considerations.
Thanks!
Cindy
We cannot endorse any specific recipes or treatments. However, we can provide suggestions for your consideration.
I would recommend monitoring the crepe myrtle, since the severity of aphid infestations can vary from year to year. If control is necessary, try one of the least toxic methods outlined in the attached Grow Green fact sheet. Often, spraying the crepe myrtle with water at high-pressure from a garden hose will work. Also, beneficial insects, like lady beetles, help keep aphids under control.
If you notice the aphid population increasing, you may want to try one of the non-systemic solutions mentioned. Horticultural oils, although generally considered safe, can sometimes cause damage. When treating a new plant, apply to a small area first to see if there is any adverse reaction. As summer approaches, consider recommended temperature ranges for application. Be sure to follow all directions on the label.
You are correct. Azadirachtin used in a soil drench, will be taken up by the crepe myrtle making its foliage toxic to any foliage-feeding insects, not just aphids. There is no guaranteed that beneficial insects will not be harmed.
https://agrilifeextension.tamu.edu/library/landscaping/aphids-in-texas-landscapes/
has more information on aphids, including their life cycle and management considerations.
Thanks!
Cindy
