Expert: C.L. Fornari - 7/10/2010

Question
i have 4 beautifull petunia plants...each one of them on a cement pot.. they growing hudge and look gorgeous... but every year at this time, underneath.. the foliage start to get brown.. dry.. and little by little will take the all plant...dont matter how big it is .. i try to make the air circulate better.. because they get so big..i put some stakes at the edge and lifted the branches a couple inches from the soil... still get it... i dont like to spray with chemicals..any suggestion?  and also i like to ask..how come all the experts nobody mention this disease on the petunia..am getting this for a list 6 years...  thank you

Answer
Riccardo,
It could be powdery mildew - that would cause what you're seeing, and it's hard to fight with just air circulation. Take a look at the leaves that are still alive, but close to the dying ones, and see if you see some very light grey colored "powdery" coating on the leaves.

The two other things that might cause this are the plant being water stressed - drying out in between waterings - and fertilizer burn.  If you're adding fertilizer when you water, and using it on a thirsty plant, it could cause the foliage to brown.

If you think that powdery mildew is the cause, you could do the following: spray the plants with GreenCure or Serenade (both organic controls) regularly starting early in the season next year. You can use them now, and cut some of the stems back in order to stimulate new growth this year. It would also help to use all new soil in the pots every year as the mildew spores will live in the soil from year to year.

I hope this helps!
C.L.