En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
2 ratings

Sunday - July 28, 2013

From: Jacksonville, FL
Region: Southeast
Topic: Butterfly Gardens, Herbs/Forbs
Title: Effects or insecticide on Monarch butterflies
Answered by: Guy Thompson


Thank you for fielding questions about plants!! Our nursery just informed us that their milkweed grower was using imidacloprid in their milkweed production. As a follow up to the question already in your database about imidacloprid on milkweed and its toxicity; Are NEW plants grown from 1) the stalks of denuded (by the poor caterpillars) plants and 2) grown from seeds from a imidacloprid treated plant - are those plants subject to the same half life time frame?


The excerpt shown below must be the one you found in out database.

"Imidacloprid is a chemical to avoid if at all possible.  It is a synthetic analog of nicotine and is slow to degrade in the environment.  According to the National Pesticide Telecommunications Network, it has a half-life in sandy loam soil of greater than one year.  In bright light it degrades faster, with a half life of 39 days. But even the degradation products that form inside plants are highly toxic to insects, and their half-life is not reported.

Imidacloprid has been implicated in the mysterious colony collapse disorder of honeybees. For this reason, certain countries, e.g., France, has outlawed its usage for many purposes.

It seems safe to assume that milkweeds treated with imidacloprid may be quite toxic to monarch caterpillars for an extended period.  Mr. Smarty Plants recommends the use of much less toxic sprays, such as Safer soap, which may be less effective on aphids but harmless to monarch caterpillars."

The half life of the chemical will be the same no matter where it resides.  The main question is the quantity that the caterpllars eat.  Imidacloprid is a systemic compound, meaning that it moves throughout the entire plant and not just the parts sprayed.  There might be enough on the denuded stalks to injure the caterpillars when they eat new leaves that have drawn the insecticide from the old stalks.  But the amount of imidacloprid that might have entered the seed would be diluted so much in new plants grown from it that there should be no danger. The caterpillars would not ingest a large enough amount of the chemical to damage them. So the conservative solution is to start new plants from seed.




More Herbs/Forbs Questions

Propagation of Cahaba lily from Columbia TN
September 03, 2011 - My cahaba lilies have so many seed pods. I would like to use the seeds properly to grow more lilies. Can anyone tell me the best way to go about it? Thank you
view the full question and answer

Perennial for cemetery plot in Massachusetts
August 03, 2010 - What perennial would work well in a cemetery plot that has very dry sun?
view the full question and answer

Need suggestions for plants for bioswales in Philadelphia, PA
August 24, 2015 - Hello, Are there a handful of species you would recommend for inclusion in bioswales throughout the US? I realize plants need to be selected based on climate, but I'm wondering if there are two or...
view the full question and answer

Shade loving plants with color for Irving, Texas
July 01, 2010 - Looking for shade loving perennials or annuals with color - native and low water. Live in Irving, Texas.
view the full question and answer

Landscaping on South Padre Island
June 07, 2008 - I'm in charge of landscaping at my beachfront condo in South Padre Island and find the wind, salt air, and heat challenging for growing almost anything. We would like to incorporate native plants, b...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center