Question
I live in mpls,mn. I have a perrenial garden approx 1000 sq feet. This has been a work in progress the past 10 years. My question is with only my columbines, some will get leaf miners, but most have been getting attacked by a green caterpillar that left alone for a day or two will completely divour the leafs. I,ve heard of using neem oil on them. Will this work? I want to be as organic as possible. In the past I've pulling the infected leaves off, but every year I get more and more from letting the seeds drop. Any help will be greately appreciated. Thank you.

Answer
Tom,

Older gardens tend to have more insect and disease problems than new gardens because pest populations buildup over time. One suggestion is to completely deep till (6" or more) the entire garden before replanting next year, essentially creating a new garden. Also, be sure to have some natural, unmanaged areas near by that can serve as a source of beneficial predators and parasites. An unmowed, weedy patch as small as 10'x10' is a good source of beneficials that will move into the garden.

Neem oil is a good material for any chewing pest. Take a look at this page http://www.livingwithbugs.com/neem_oil.html for some background information about neem oil. You might also consider spinosad as an alternative to neem oil. Spinosad is a natural material made from a soil microbe and is very effective against caterpillars. Take a look at this page http://www.livingwithbugs.com/spinosad.html for more information.

Good luck with your garden this year.

Jack DeAngelis, PhD
Extension Entomologist (ret.)
author Living with Bugs: http://www.livingwithbus.com/bug_book.html