Expert: Mike Mascio - 6/1/2007

Question
I planted several hanging baskets (coconut lined) with petunias, mixing purple, white, and pink.  I also planted some of the same in the ground.  Most of my petunias are doing great; however, one group of the pink which had been planted in the ground, began to die.  When I would lift the stem, it would "break" off in my hand.  There was one remaining stem which was nice and green, and I decided to plant it in one of the hanging baskets, and put a red verbena in the area it had been.  That was probably about a week ago, and now over half of that hanging basket is starting to wilt and die. And strangely, 2-3 individually planted petunias located below the basket area are also starting to wilt. (The red verbena seems to like its new home.)  I have found three green striped single horn caterpillars (one about 4" long) on other plants near the original pink petunias.  Two were on a gaura lindheimeri, which had been doing beautifully, but is not looking good now.  
I live in north central Texas, where we have been having unseasonably large amounts of rain.  

Your thoughts and advice would be greatly appreciated.  

Answer
I doubt the caterpillar is your problem. When they infest a plant, they eat the leaves. The exception is the cutworm, which eats the base of the stem and literally saws the seedling to the ground.

What has most likely occurred in your situation is that your plants have contracted a fungus disease. Some varieties are more susceptible than others, but a soilborne disease can infect any plant.

Once the plant has the disease, it will spread it to others. That is what porbably happened after you transplanted to the hanging basket.

You can spray the plants with a copper-based fungicide to stop the disease from spreading further. You can purchase these products at any garden center. Most recommend 3 tsp. per gallon of water every 10 days until the disease is under control.

By the way, you can also eradicate the caterpillars with a product called BT, short for Bacillus thuringiensis, and more commonly sold under the brand names Dipel or MVP. It
is a dust that is non-toxic to humans and beneficials but highly effective against caterpillars and hornworms. You can purchase this product through on-line catalogs such as Gardens Alive or locally at many garden centers.

I hope this answered your question.  Please write again if I can ever be of assistance.

Regards,

Mike.