Question
I have a black fuzzy like growth on all of the new blooms of my petunias, therefore the blooms don't blossom.  What to do?

Answer
Hi Trudy,

Since you have observed dark fuzzy growth on the flowers, it is likely that you have a fungal problem.  The most likely culprit is Botrytis blight.  This disease is common on petunia especially in humid areas.  It can cause symptoms from minor spotting on the petals to complete loss of the flowers.  

Your management should begin by removing and discarding any faded or blighted flowers and leaves.  The fuzzy growth contains thousands of spores that can initiate new infections.  By removing them, you are reducing the chance of spread to new flowers.  You may also need to remove debris from around and under the plants.  It is best to do this during the hottest and driest part of the day to avoid the chance that your actions spread the pathogen to new plant parts.  If you use cutting tools (pruners), you should dip them in a disinfectant solution between cuts such as weak bleach solution (1 part household bleach, 9 parts water).

Avoid overhead irrigation.  When watering these plants, place the hose directly at the base of the plants.  Water from overhead irrigation will splash spores to new plant parts and promotes new infection.

Promote rapid drying of plant foliage.  This can be done by watering in mid-morning or early afternoon.  If water sits on the flowers and leaves throughout the night, it favors disease development.  If your plants are tightly packed, you may consider thinning them which will increase air circulation through the canopy and promote faster drying.

In the fall, remove and destroy plant debris from infected plants.  The fungus survives in dead plant tissues in resistant structures called sclerotia.  By removing the debris, you will remove much of the inoculum (pathogen spores) and reduce the chance of infection next season.

It may be necessary to use fungicides to control the disease.  There are many products available including basic copper fungicides, captan, chlorothalonil, etc.  Since products vary by garden center, you can check the label to see if the product is labeled for control of botrytis blight.  Be sure to check the label instructions for mixing rates.  The products are most effective if applied in the spring during cool and wet weather.  However, since you are continuing to have a problem, it will be advantageous to make an application at this time.

For more information about this disease and a few images, you may want to visit the following website:  http://greenindustry.uwex.edu/problemdetails.cfm?problemid=1374

Good luck!