Tooele Transcript Bulletin – News in Tooele, Utah
image Caterpillars work their way into plants to eat away your hard work. But there are things that can be done to fight against them.

August 15, 2013
Stunted flowers? Fight back against nefarious creepers

“What is eating you?” you might ask your petunias, flowering tobacco, geraniums or other garden flowers that looked good a week or so ago but have quit flowering now. The blossoms suddenly developed holes, were reduced to stubble and quit sending out new blooms altogether. All that is left are the now-withered old blooms on an otherwise lovely green plant. What could be the problem?

The first conclusion might be the need for a dose of fertilizer and perhaps your plants do need it. Although such flowers benefit from a dose of fertilizer during the summer, lack of fertilizer usually results in fewer blossoms — not a sudden, complete absence of them. When the few flowers that do open look chewed, they probably are chewed.

The probable culprit is tobacco budworm, Helicoverpa virescens, or the geranium budworm, Heliothis virescens. The two look a lot alike and have very similar eating habits. Both are hard to find as they are 1/4 to 1 1/2 inch-long, light colored, greenish or brownish striped caterpillars. They are hungry little pests and are particularly attracted to solanaceous plants such as flowering tobacco (Nicotiana,) petunias, and occasionally even the blossoms of tomato and potato plants. Petunias and Nicotiana are the most vulnerable, but these pests aren’t choosey eaters. Although they eat pin-sized portions at each bite, they can make ragged stubble of entire blossoms in short order.

They eat so well, in fact that they take on the color of the plant they have been feasting on. That color combined with their tiny size makes them rather difficult to see. The most obvious evidence of their presence is holes in buds, chewed leaves, and black droppings.

The geranium budworm is most adapted to survive in warm climates, but, if it can find a sheltered area around a building or on geraniums brought inside to winter over, it can survive through cold winters.

If the infestation is not too serious, and you can find them, you may get adequate control by handpicking them. Insecticides are moderately useful for controlling these pests but they hide inside the blossoms where sprays do not reach them. A better choice is Bt, Bacillus thuringiensis. There are several advantages to using this product as it is a bacteria that is lethal to caterpillars but nontoxic to mammals, bees, and most other insects. The larva eats the treated leaf and develops a fatal stomachache. Within hours, it stops eating and within a couple of days, it will die.  Bt is the active ingredient in Dipel and Thuricide.

Spray early, before damage is extensive, since the smaller caterpillars are more susceptible to BT than older ones. Apply sprays thoroughly to the tops and bottoms of leaves until the solution drips off. You may have to reapply the product as new eggs hatch out.

 

 

Tips for the Week

1. Fertilize lawn six weeks after last fertilization

2. Watch for tomato hornworms — they can usually be controlled by hand picking

3. Destroy snails and slugs and dispose of the carcasses. The eggs inside may remain viable and hatch out next year.

4. Watch for spider mites in vegetables, fruit trees and landscapes. Affected plants develop brown or gray stippled leaves. Check by tapping foliage over a sheet of white paper. Watch the dust that falls to the paper. If it begins to crawl around, you have spider mites.  Wash the backsides of the leaves with a strong stream of water or insecticidal soap.

5. Avoid using miticides unless the problem is severe, as these chemicals also kill the predatory mites which help control their plant-feeding cousins.

6. Continue to spray apple trees through Labor Day to protect the fruit from coddling moth.

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