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Sunday, July 5, 2015

Holes in Geranium Leaves Probably Tobacco Budworm

Q. I have two pots of geraniums facing the morning sun under a covered patio. The sun moves away at about 10 am. They look fairly good. I am watering them three times a week and temperatures are 101 to 111 degrees during the day. The plants have beautiful green leaves but they have holes in them. What's causing this and what can I do to help minimize or eliminate the holes?
Corn earworm, Close relative to tobacco budworm

A. The damage reported to me by my readers have been primarily on two plants; geraniums and petunias. Both of them reported a loss of color which means they stopped flowering. Tobacco budworm normally infests flower buds and so a loss of color is usually the first thing that is noticed. However, once flowers have been destroyed and occasionally even when they are not destroyed we see damage to the foliage or leaves.

It is most likely tobacco budworm which is a close relative of the tomato fruitworm and the corn earworm. These are virtually the same insect but infest different plants.

However, the tobacco budworm is a little bit more difficult to control in geraniums. The tobacco budworm normally attacks the flowers and causes the plants to stop blooming. But if there are no flowers to attack, they could go after leaves.

This budworm also attacks petunias and causes a loss of flowering. Another little present they leave behind are small black fecal poop on the leaves.

This is the larva of a moth so you can try either Bt or Spinosad sprays on the leaves. I think Spinosad will give you better control in my opinion in this particular instance.

You can also try a soil drench and spraying the foliage with a synthetic pyrethrum product. These are insecticides that have an active ingredient on the label ending in -thrin.

One of these products, or all of them, should give you some control and they are not bad products to have on hand for other things as well.

Some further reading on tobacco budworm
Fact sheet on tobacco (geranium) budworm from Colorado State University
Tobacco budworm on petunias can be managed with Bt in California Agriculture (1992)
Updated information from the University of California (2013)

Why do I select Information only from Colorado and California? First of all, Colorado State University is my Alma Mater but not only that they are in the arid West and information from Colorado, New Mexico, Utah more closely resembles what is needed in Nevada, or the desert, than information from Florida or Minnesota. Information from California is needed by Mojave Desert residents because many of the plant materials grown in the Western deserts were purchased and exported from California. It is always best to obtain information from valid sources in climates that are similar to your own.

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