Hello Ralph,

Pesticides have to be approved by the EPA and state department of agriculture—much like the FDA has to approve drugs before they are used by the public. Each pesticide is formulated to treat a specific disease or insect pest on specific plants. The label explains how, where, when and on what plants to use them. The label is the law and using a pesticide for something not stipulated on the label is against the law. To combine different pesticides seems capricious. You will not know what the eventual result will be. There are many formulae on the internet advising mixtures but it is not the position of Extension Responders to endorse these mixtures.

That said, read the following on how to treat Magnolia scale: Controlling it depends on timing. The scale is most vulnerable when the insect is in the crawler stage and looking for a place to feed which is usually late August through September. Adult scale insects are usually protected from chemicals, so spraying is ineffective. If you applied insecticide at the correct time one year, you should probably not have to treat the tree again. However, trees that are stressed are more prone to attack by insect pests. To ensure that the tree is healthy, keep it properly watered (1 inch per week), mulched and remove damaged or diseased branches. Also, excessive fertilization can promote too rapid weak growth and attract pests. Read about magnolia scale here:

https://www.canr.msu.edu/news/check_magnolias_for_magnolia_scale_now

You will see in that article that controlling the scale depends on the stage of the insect. June to early July is the time to apply systemic insecticide to the soil beneath the tree which is absorbed by the roots and will move from the roots into the branches.

The next stage in the insect’s life is the active crawler stage which occurs in Michigan in August through September when you can spray with a contact insecticide. You should not need to use the second application if you do the first.

You can read more about magnolia scale here: https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-pests/magnolia-scale-neolecanium-cornuparvum

MSU’s Enviro-weather site has a tool which states when the crawlers are active.

http://msue.anr.msu.edu/news/magnolia_scale_is_starting_to_appear_on_magnolias

The presence of the wasps and insects around the tree is likely due to the honeydew which is excreted by the insect and can lead to sooty mold to branches or plants below the tree. Read more here: https://northerngardener.org/magnolia-scale/

If you use a pesticide, always read and follow the instructions on the label for the best results. Ensure that the insecticide can be used on the magnolia and will affect the insect you wish to treat.

Finally, if your tree is too large for you to treat, consult a certified arborist. Go to: www.treesaregood.org, the website of the International Society of Arborists to find one in your area.

Thank you for contacting Ask Extension.