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

Yaupon hollies dying mysteriously
July 16, 2014 - I have a row of yaupon hollies (Ilex vomitoria) that I keep trimmed like a hedge. They were all healthy for many years. Two years ago one of them died and I removed it, leaving a gap in the line of h...
view the full question and answer

Disease or insect damage on a Mexican plum
September 08, 2013 - Help, Our Mexican plum tree is about 13-14 years old. Earlier this year we noticed the trunk is oozing black stuff and whole branches are dying off. We have watched as our beloved tree has lost most ...
view the full question and answer

Leaves on new water oak turning brown from Matagorda TX
May 30, 2013 - We had water oaks planted in January when they had no leaves. Leaves came on but are now turning brown.
view the full question and answer

Stressed live oaks from Lakeway TX
August 19, 2013 - I have some Live Oaks who appear to be stressed (Ball Moss is becoming very prevalent on some of them) during the drought in Central TX. How often and how long should I water them? Thank you very much...
view the full question and answer

Problems with mature cottonwood in Justin TX
September 17, 2012 - I have a very large, 90" circumference, approx 60' tall, cottonwood tree in my front yard that appears to be sick. The trunk splits at about the 4' level into 2 parts. at that split is a 10" wide...
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
© 2014 Lady Bird Johnson Wildflower Center