Insecticide Spray Application on Linden Trees For Aphids - November 2020

A week or so ago, I posted about how our pair of espalier Greenspire Linden trees had come down with an infestation of aphids.  I asked the Master Gardener at the University of Illinois and they confirmed they were Linden Aphids and recommended a synthetic insecticide.  They also pointed me to this post from Colorado State University that lays out the two types.

Persistent Contact Insecticide Sprays. And Systemic Insecticide Sprays.

First the latter:  systemic.  These are ones that 'move through' the tree and can handle aphids that you can't reach with a topical/contact spray.  From CSU:

A few types of insecticides have the ability to move into the plant and move systemically. Because of this mobility these systemic insecticides can provide better plant coverage and often provide better control of aphids than do non-systemic insecticides. Systemic insecticides are also able to kill aphids that are protected within a leaf they have curled.

Timing of application is also a consideration when you are choosing between the two.  From what I've read, it is best to apply the systemic insecticides via the ground in the late Winter - before the tree comes to life.  You have to move the soil aside and keep the area wet to ensure uptake.

But, right now?  As the leaves are falling and I'm dealing with nymphs, active aphids and eggs on the buds, I wanted to try a persistent contact variety.  What they have for sale at Home Depot is this stuff you see below:

Comes as a hose-attachment and lets you cover the tree.  With the weather being so nice this past week, I used the opportunity to apply this stuff more than once.  Here, below, is the tree soaked with this solution.

Now that I know what I'm dealing with, I'll be keeping a lot closer eye on these trees in the Spring.  I'll also get in a position to apply a systemic insecticide early next year.