Question
Jim,
I have 5 10-12 ft ash trees which I treated in summer of 2007 for wooly aphids. I used a systemic insecticide which worked well for over 1 year. This fall, after about 75% of the leaves yellowed and fell off, I noticed the remaining leaves turned brown and curled up. The woolys are back, should I treat systemically again, or wait until spring?
Thank you for your help.

Answer
Systemic insecticides depending on the type and application method will last about 6-9 months or usually the growing season. Most labels say 12 month. They will work best in the spring since this is when the plant is growing the best and the movement of the insecticide into the system will be the fastest. Now the plants are shutting down for the fall and winter and the systemic would not move into the trees system as well and the insects will not be present long so an application now would be wasted. wait until the spring.