Geranium Budworm

Find a SoCal garden center near me for the best selection of plants, including geranium budworm-resistant varieties.

Written by Richard Flowers, ACCNP Green Thumb Nursery- Ventura

Ivy Geraniums and Zonal Geraniums are one of the most popular plants around because they both provide a lasting flower display in a multitude of different colors throughout the year and are easy to grow.  The Ivy Geranium is commonly used for hanging baskets and ground cover applications, while Zonal Geraniums are more bushy and can be used in the foreground of taller growing perennials. Both types of plants are excellent growing in decorative containers. Many times gardeners become frustrated because the flowers become damaged which makes the plants appear unattractive because their floral displays are ruined. More than likely the culprit is a small worm that eats the flowers. Read on and I will provide you more information on what this creature is and the best management practices are. 

If you ever seen your beloved Geranium flowers get ruined, you will most likely become the victim to what is commonly called Geranium Budworm which is also called Tobacco Budworm. Geranium Budworm feeds on the buds and petals of many commonly grown flowers, including Geranium, Petunia and Nicotiana. The most common harm is associated with Geranium hence the name was assigned to it as such. The damage associated with this organism include flowers failing to open and small holes that appear in the flower buds. The petals of emerged flowers are chewed, giving the flowers a ragged appearance. Oftentimes the flower buds will have visible holes or small specks of frass (worm droppings). Many times you will see irregular or round holes in the leaves.

When looking for the creature and with careful observation you will see a yellow or greenish worm with a brown head that has many black microspines that make the body feel rough to the touch. The caterpillar measures 1/25 to 1 1/2 inches long, depending on its age. When you look around more closely you’ll you see a moth with a wingspan of about 1 1/2 inches. The wings are light green with brown overtones and a few wavy, cream-colored bands. These moths are the adults. You will see moths fluttering around your Geraniums in the early evening with the onset of warm spring weather. (Be advised, in moderate coastal climates, moths can be seen almost year -round). These females lay single eggs on buds or leaves, which will soon become the “worm” or caterpillar. During daylight hours, the worms often hide around the base of the plant. The caterpillars become full-grown in about a month, drop to the soil and pupate in cocoons. Sometimes you can see cocoons attached to leaves or buildings. These Budworms attack the flower buds of developing flowers resulting in poor or no flowering at all. The amount of damage the insects cause progresses through the growing season, becoming most noticeable in late summer. In moderate coastal climates the problem can exist almost year-round.

Now that you know how to identify them and what kind of damage they do, it is  necessary to understand the management techniques. I will provide you several ways you could employ to help minimize damage.

If you have a really small area or don’t want to spray insecticides and don’t mind handpicking the caterpillars. Simply lift up the worms and drop them in a bucket of soapy water. Don’t worry the worms don’t bite. To be most effective with this approach it is best to do this practice when they are active which is at dusk. 

Another organic approach without using insecticides to help control the Budworm is to prune off the buds on the Geranium that have visible entrance holes or small specks of frass, then dispose of them in a plastic bag or away from the plant thus breaking their life cycle. In my own garden, I have Ivy Geraniums spilling over the sides of a large decorative pot. I monitor my plants on a routine basis. If I start to see evidence of harm, at dusk, I snip away the  little damage I have and I am done, keeping the worm population down to a minimum. I will only resort to using any insecticide if it is absolutely necessary as a last resort. 

While still being an organic or natural way to control the Budworm the insecticide containing Bacillus thuringiensis also known as Bt) can be used. It is  often sold as Bt Worm Killer or Caterpillar Killer. This is an effective biological control when used on some plants.  However, the “worm” must eat the Bt in order for it to be effective. Personally, I find that plants such as Geranium, where the caterpillars drill into the buds and eat little of the outside surface, thus making Bt not effective. Others have noted that Bt Caterpillar Killer works satisfactory to their needs. More than on application may be necessary. 

Another insecticide that is natural or organic is one that contains Spinosad. I find it  easier to remember the name Captain Jacks . Captain Jacks is a derivative from the rum making process. I find that Captain Jacks to be more effective on Geraniums than Caterpillar Killer. More than one application may be necessary.

If one chooses to use a synthetic insecticide, the old stand by and most reliable is Malathion, which will take care of the problem in a heartbeat. More than on application may be necessary. 

Geranium Budworm is difficult to control if you have a large population, but oftentimes nature will take its course and the plant will re-bloom and recover again on its own. The Budworm does not kill the plant , it just ruins the flowers, and causes cosmetic damage to the leaves. In my garden the bud worms feast on my plants, it doesn’t cause concern to me because I know the the plant will come back on their own because Geraniums are tough, durable and resilient plants. You can also keep your plants healthy and vigorous by watering properly and fertilizing with an organic fertilizer which allows your plants to grow stronger and thrive thus helping to minimize insect and disease attacks.

A note on using any insecticide. It is best to read, follow and understand all printed documentation the insecticide label has before applying the chemical. 

If you have any bug or plant related questions feel free to stop by your favorite Green Thumb Nursery we will be happy to help you out. 


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