Assistance for the Home Gardener from the Contra Costa Master Gardeners Help Desk
CCMG Help Desk Response: Thank you for contacting the Contra Costa County Master Gardeners. It's always a good idea to check the toxicity of a pesticide before using it! Neem oil is a naturally occurring pesticide found in seeds from the Neem tree (Azadirachta indica). While Neem Oil has a very low acute toxicity rating for people and other mammals, it can be toxic to bees if not properly applied.
The University of California considers Neem Oil as moderately toxic to bees and recommends application only during late evening, night, or early morning and when plants are not blooming, i.e., when bees are not typically out foraging.
The following UC IPM (Integrative Pest Management) website provides additional information on Neem Oil (http://www.ipm.ucdavis.edu/TOOLS/PNAI/pnaishow.php?id=53). When applying any pesticide it is very important to follow the label directions precisely, take all necessary precautions, wear appropriate safety equipment, and only apply the pesticide where appropriate and necessary for a specific pest. The following UC website provides guidelines on the safe and effective use of pesticides http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74126.html.
If you are interested in reading more about pesticides and bees, UC recommends the article "How to Reduce Bee Poisoning from Pesticides" by Oregon State University on the web at http://www.ipm.ucdavis.edu/PDF/PMG/pnw591.pdf.
Please feel free to contact us if you have any additional questions.
Contra Costa Master Gardeners Help Desk
Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/