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
Not Yet Rated

Friday - May 30, 2014

From: Morrisville, PA
Region: Mid-Atlantic
Topic: Diseases and Disorders, Herbs/Forbs
Title: Mildew on phlox paniculata from Morrisville PA
Answered by: Barbara Medford

QUESTION:

My Phlox paniculata, all 7, have powdery mildew. I read about using NEEM to combat the mildew. NEEM is organic but the bottle says it is also an insecticide. The phlox are near my milkweed and goldenrod, I want to be careful what I use. Can the Phlox be saved?

ANSWER:

Please follow this plant link, Phlox paniculata (Fall phlox),  to our webpage on the plant and see if the growing conditions in your garden match those of this plant. From that page, we extracted this: "Conditions Comments: The plant needs at least 6 hrs. of sun per day. Powdery mildew is a frequent problem."

Next, please read this article from Colorado State University Extension Powdery Mildew. From that source, we want to emphasize this paragraph:

"Conditions That Favor the Disease

The severity of the disease depends on many factors: variety of the host plant, age and condition of the plant, and weather conditions during the growing season."

Powdery mildews are severe in warm, dry climates. This is because the fungus does not need the presence of water on the leaf surface for infection to occur. However, the relative humidity of the air does need to be high for spore germination. Therefore, the disease is common in crowded plantings where air circulation is poor and in damp, shaded areas. Incidence of infection increases as relative humidity rises to 90 percent, but it does not occur when leaf surfaces are wet (e.g., in a rain shower). Young, succulent growth usually is more susceptible than older plant tissues."

Scroll down that page to the area on "Control," which includes some suggestions on chemical controls.

Those of us who live in blazing, drought-stricken Texas don't tend to think of Pennysylvania as "warm, dry," but everything is relative, and we believe the growing season for  your phlox probably is warm and dry. However, as noted above, if you don't have  6 hours or more of sunshine directly on the plant it is probably going to be very mildew prone. Possibly when you first planted your phlox, shrubs and trees around it were small, and the phlox was not very thick. You can certainly try thinning out the phlox, possibly even some pruning of overhanging woody branches, but NOT IN VERY HOT WEATHER!

 

From the Image Gallery


Fall phlox
Phlox paniculata

Fall phlox
Phlox paniculata

More Diseases and Disorders Questions

Need help with a fungal disease in oak trees in Austin, TX
April 26, 2012 - Two adjacent oak trees in my yard are showing distinct symptoms of Sudden Oak Death. Most notably, the lowest ten feet of their trunks have several bleeding cankers with thick, tarry ooze and no accom...
view the full question and answer

Watering Houseplants with Soapy Water
August 22, 2011 - I accidentally watered my house plants with a container that had a some dishsoap in it. Will they be okay? One of the plants is a 20yr old cactus, with small roots.
view the full question and answer

Diagnosis of problem with Parsley hawthorn
August 06, 2007 - I have a Crataegus marshallii (Parsley hawthorn) that is about 3 years old. It leafed out this spring and flowered lightly. As the summer has progressed, though, the leaves have been dropping premat...
view the full question and answer

Treating cuts in tree trunks
November 21, 2009 - We have two young trees that deer made bad cuts in the trunks. What can we put on cuts to keep bugs and disease from getting in them.? Thank you.
view the full question and answer

Hypoxylon Canker removal in Austin TX
March 26, 2012 - I have several oaks that appear to have been killed by Hypoxylon atropunctatum from last summer's drought. Is it safe to cut them down in March or does that risk spreading Oak Wilt too. Should I ...
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