Homegrown column Sept. 12, 2009
We have a petunia plant which has small worms which eat the blossoms. What suggestion do you have to get rid of such worms?
What you have is an insect that bothers lots of people throughout western Colorado.
It’s called a budworm, and like the name implies, it feeds primarily on the flowers and buds of plants. This particular one is called the tobacco budworm, or geranium budworm. This little monster is actually a significant agricultural pest on cotton and tobacco.
The tobacco budworm primarily feeds on the flowers and buds of geranium, petunia and nicotiana, among others, though I seem to see the problem much more frequently on geraniums. They’re sneaky little devils, just eating the flowers and not the leaves, so there’s really no obvious damage to the plant to warn you early on of what’s going on. It’s not until a couple of months have gone by and it hits you that the pretty petunia hasn’t bloomed for a while. When you look closer, you’ll see the eaten-out flower buds, and they’re usually small black specks on the leaves which are the insect’s droppings.
People often fail to see the insects because they have the ability to blend in really well with their surroundings. The caterpillar will vary in color from brown to green to red, depending on what it’s eating. I’ve looked for them in the past and looked right past them hiding on the plant.
Controlling this guy takes a bit of persistence. Budworm is resistant to many of our old-line insecticides, so we’ll recommend the newer synthetic pyrethroids such as Permethrin, Cyfluthrin or Bifenthrin. Spinosad should also do a pretty good job if you’re looking for a more “eco-friendly” spray.
You’ll have to spray pretty regularly to keep it under control because we get several generations of this insect each summer. I like to spray anywhere from once a week to twice a month. Be sure to completely cover the plant with the spray, including the undersides of the leaves and the base of the plant. Because there is more than one generation a year, you’ll have to plan on spraying throughout the summer.
There is one thing you can do to try to make the problem less severe next year.
Tobacco budworm really isn’t hardy here; we tend to get a bit too cold for it.
However, it can flourish in pot that’s kept in a warmer spot over the winter or a patch of garden soil that’s in a warm microclimate such as a sunny spot right next to the house. Because the insect spends the winter as a pupa in the soil, disposing of the soil in the pot or turning over the soil in the flower bed in early to mid-November to expose the pupa to the elements will kill most of them.
Unfortunately, we can still get this pest from bedding plants that were shipped in from warmer areas of the country or even the adult moth flying in from down south, so it’s
probably something that we’ll be dealing with for the foreseeable future.