It's not always possible to buy organic as sometimes it's not available, in season, or the cost is prohibitive. Pesticide Action Network UK (PAN) test regularly and are a handy reference guide to what is best in the UK. EWG.org are similar in the US.
Refer to this website seasonally to see what fruits and vegetables test best, and what you should avoid unless organic.
Deborah McTaggart is a Nutritionist with a special interest in Performance Nutrition, practising in Barnes, London. Please contact me here for more information.