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?

Share

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
1 rating

Monday - March 07, 2011

From: Boerne, TX
Region: Southwest
Topic: General Botany, Pests
Title: Half-life of the insecticide imidacloprid
Answered by: Guy Thompson

QUESTION:

How long do systemic insecticides such as imidacloprid (Merit) remain active in nursery grown plants? Asclepias curassavica (tropical milkweed)is frequently grown with imidacloprid to prevent aphids but it also kills monarch caterpillars utilizing the milkweed. How long will the milkweed be toxic for monarch caterpillars? Thanks.

ANSWER:

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.

 

More Pests Questions

What causes rock rose branches to snap off?
August 30, 2013 - my small texas rock rose branches keep snapping in the center. What is causing this and what can I do?
view the full question and answer

Fungus gnats on indoor plants
July 09, 2007 - Hello, I live in Austin and I work in an office where we like to have plants. Recently we started to get these annoying tiny, little nits, how can we get rid of them without harming my plants. Help th...
view the full question and answer

Danger of lichens damaging trees
September 26, 2007 - My mom lives east of Buda, Texas where she has planted many different kinds of trees, which are all over 10 years old. Now, they all have a moss or lichen growing on the bark of the trees. She is worr...
view the full question and answer

Herbicide on Habiturf from Austin
May 31, 2014 - Can you recommend an herbicide that is safe to use on a Habiturf lawn? I followed the directions to put in a new Habiturf lawn about a month ago. The grass seedlings are doing well in places, but ...
view the full question and answer

Problem with leaves of Texas Ash in Austin
May 21, 2012 - We purchased a 3' to 4' Texas Ash in March 2012. The past few days I noticed new leaves at the top are curled under, have a milky substance on them, and more than a few ladybugs on them. What is thi...
view the full question and answer

Smarty Plants's Facebook profile Support the Wildflower Center by Donating Online or Becoming a Member today.

Mr. Smarty Plants wants you to be his Facebook friend. Click the Facebook icon to add yourself to Mr. Smarty Plants list of friends.
E-NEWSLETTER | BECOME A MEMBER | DONATE NOW | MEDIA | SITEMAP | STAFF
© 2015 Lady Bird Johnson Wildflower Center