It may be the fact that you used alchohol or maybe sprayed to frequently with the pesticide.
What do you base this answer on?
Yellowing can have a lot of reasons. More common reasons are overwatering (The roots stay very wet for a long time), or too much moving of the plant. This next to insect infections, but you should have that problem if you have used a systemic insecticide..
Please post a few pictures: Of the whole ree, and of some leaves that are turning yellow and of individual branches.