Native Plants
![](../_images/smarty_plants.gif)
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.
Did you know you can access the Native Plant Information Network with your web-enabled smartphone?
Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.
![](../_images/mr_smarty_plants_logo_web_200w.jpg)
rate this answer
![](../_images/star_00.gif)
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
More Diseases and Disorders Questions
Leaf drop from maple tree in Minnesota
August 15, 2008 - I have about a 30 ft maple tree in my yard, last fall I trimmed it pretty good because the branches were getting low where you could not walk under it or get grass to grow. This is the 2nd time in abo...
view the full question and answer
Leaves falling off recently transplanted mature Mountain Laurel
July 05, 2006 - I have recently purchased a Mountain Laurel for my backyard landscaping. It is a fully matured ML standing over 9 feet tall by 6 feet wide. Since it was planted (about 6 weeks ago) it has been losin...
view the full question and answer
Growths on Shumard Red Oak leaves from Katy TX
April 01, 2013 - Our beautiful Shumard Red Oak has developed lots of light green grape like growths on the leaves. Please inform us what this could be and how we should treat it?
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
Coreopsis failing to bloom in Sonora CA
August 04, 2009 - My Coreopsis buds form and then die. Very few open. The plants are two and three years old, in a clay type soil. Is it possible they're getting too much water, and that is whats making the buds die ...
view the full question and answer
Support the Wildflower Center by Donating Online or Becoming a Member today. |