If you are seeing hornets coming in and out through cracks in the retaining wall, then a great product to use would be Tempo 1% Dust. You should apply the Tempo 1% Dust with a duster such as the B&G Bulb Duster 1150 and direct the dust into the cracks in the wall where you are seeing the insects enter and exit. You may also want to have Wasp Freeze on hand for quick knockdown of flying insects in the area.
To get into those higher areas, you could use the Dustick Duster applicator. Tempo 1% dust is the most effective dust to treat for hornets and yellow jackets. Be sure to treat in the times of the day when they are less active (earlier morning or later evening). You may also want to use a ready-to-use knockdown insecticide such as PT Wasp Freeze II. This spray will spray up to 15 away for safe and quick knockdown of flying, stinging insects.
Tempo 1% Dust will work great for wasp and will not harm Evergreen Shrubs.
No, Tempo 1% Dust should be used only as directed on the product label as a dry insecticide formulation. You can use either Tempo SC Ultra, Tempo Ultra WP, or Tempo WSP Ultra if you would a concentrate to apply as a spray.
According to the Tempo 1% Dust label, If the product is inhaled do the following.
* move person to fresh air.
* If person in not breathing, call 911 or an ambulance, then give artificail respiration, perferably mouth-to-mouth if possible.
To remove Tempo 1% Dust, you can simply vaccum the area and then rinse with soap and water. You should launder any fabrics that you think may have gotten the dust on them. Be sure to wear gloves while cleaning.