I have Root Aphids on some good-sized outdoor plants. I found them popping out of the ground when watering by hand. I did a drench with hydrogen peroxide and suspect the 4 to 1 ratio with 3% is too weak. I want to use some DE. Should I gently work it into the soil, or leave it on top? It seems reasonable to maybe do both. Thanks in advance. Look closely and you will see the little bastards. There are thousands. Ken