Question
I live in the Willamette Valley in Oregon, and have had excellent success in gardening until I planted three petunia plants in a terra-cotta pot last month (keep them on porch). They bloomed once, but the next day the blooms had been eaten by aphids. I checked for other pests and found several skinny, light-green caterpillars, cankerworms? Not sure. I sprayed the plants with a foamy dish-soap and water mix, didn't seem to help. Plants stopped growing and look very sparse. I bought some pesticide, didn't help either. Today I cut away some of the plant and noticed that the stems are hollow clear down till the dirt. What should I do, can my petunias be saved?  

Answer
Molly, you can try cutting the petunias down to about 3" and hope for one more flush of blooms in about 4 weeks.  But based on your description, the plant is probably beyond saving, especially if the stem is hollow.

As with all insect infestations, it is crucial that the problem be addressed early.  Sprays are effective but are strictly contact controls.  They have very little long-term effect.  The best solution is powdered insecticides.  I personally use rotenone, an organic pesticide derived from other plants.  Sevin dust is also effective, but it is a harsh chemical.  The only downside to dust control is that it must be reapplied after a rainfall.  

I also interplant garlic and onions near plants that are susceptible to aphids.  Aphids hate the smell and will normally not infest plants that are planted near garlic.

I realize none of these answers solves your current problem.  But hopefully they will come in handy should you ever experience a similar problem in the future.

Regards,

Mike