Aphids vs. Ladybugs vs. Pesticides
I live in Saratoga Springs, UT. We have a number of fruit trees. We have found aphids on two of them (apple and plum) with relatively few on the apple and (in my opinion) enormous amounts on the plum tree. I went out to spray it with pesticides recently and noticed a fairly substantial group of ladybugs on the tree too, presumably enjoying their feast. I've heard that ladybugs are great to have around to kill aphids. My question then is if I should spray pesticides on the tree and kill the aphids (which may or may not work), which may also unfortunately kill the ladybugs? If I don't spray, is it likely that the ladybugs will 'win' or with a fairly substantial aphid population, is my tree at greater risk if I don't spray it? See attached pictures for an idea of the scope. Thank you!
Great pictures, thanks! Yes, that is a lot of lady bugs, They will eat aphids, but more importantly, they each lay about 300 eggs, and the young lady beetles (called larvae) will eat even more. So If it were me, i would wait at least a week to 10 days to see how well they have done their job. The ladybeetle larvae will look like little black alligators, sometimes with an orange stripe.
If you don't want to wait, you could use insectidal soap, which is safer on beneficials.