Insects and Systemic Drenches

I like using systemic drench (imidacloprid) as a good way to control insects that attack our plants and trees. You pour (not spray) the insecticide around the base of the tree and the tree moves the insecticide inside so non-target insects are not inadvertently killed. However - what seems to happen is the DIY person walks outside in late spring, glances at their tree or rose bush to see it covered in Insects...It can be very upsetting creating a dramatic reaction to do something ...

Insect control is very dependent on timing. The biggest mistake I see DIY home owners doing is a systemic drench thinking the tree will immediately uptake the insecticide and kill all the bugs. This is where timing is everything. You need to do the drench so the plant has enough time to pick up the product through it's roots and translocate it throughout the limbs and into the foliage.
 A good case in point is trying to control aphids on Ash trees - you will have better control if you do the drench at leaf drop in the Fall so the Ash has the insecticide throughout it's canopy in the Spring.