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Archive for Thursday, July 17, 2008

Butterfly larvae, caterpillar pests are strikingly similar

July 17, 2008

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A plethora of caterpillars have hatched in the last few weeks, leaving leaf skeletons and bare stems in their wake. If you are a victim of these sneaky little critters, do not despair - your trees and flowers are salvageable.

If the caterpillars are still chewing away at your landscape, determine if they are good guys or bad guys before attempting a counterattack. The larva of a swallowtail butterfly is eating parsley in my garden right now, but I am sacrificing for the sake of the butterflies (and I planted more this year in anticipation of the swallowtails' arrival).

Little caterpillars are harder to identify than their winged parents, though. Insect books rarely include all stages of insect life, sometimes leaving us to a guessing game. A caterpillar can always be put into a glass jar with slits cut in the lid for air and extra leaves of whatever he is eating. Then, watch firsthand as the larva builds either a cocoon or chrysalis and emerges as a moth or butterfly, respectively. Remember to identify the adult before you release it back outdoors!

A first step to identifying caterpillars is by considering the host. Oak trees, for example, are really getting chomped, and most of the caterpillars that prefer these trees are grouped in with the bad guys. With names like variable oakleaf caterpillar, unicorn caterpillar, and saddled-prominent caterpillar, how can you even think about what they might turn in to? Did I mention that all of these caterpillars are extremely hairy?

Even more common on oaks and other broadleaved trees are close cousins, yellownecked caterpillars and walnut caterpillars. Since these guys like to gang up on poor defenseless little oak trees, keep a close eye on your landscape. Pick them off by hand, or use a pole pruner to remove branches that are loaded with worms. The earlier you catch them, the less damage they cause.

The harder-to-identify caterpillars leave you to make a judgment call. You can get rid of the young insects and be done; you can learn the difference between a cankerworm and a tawny emperor larva, or you can simply leave the worms to their wiles.

If you have variable oakleaf caterpillars or other caterpillar pests in your tree, try picking the insects or cutting them out of the tree as your first option. Bacillus thuringiensis is effective when the larvae are still small. Permethrins and spinosad are effective as well. If you wish to use synthetic insecticides, there are a large number that are effective. Check the label for the caterpillar in question and make sure the insecticide is safe to use on the host plant. If treating fruit trees, pay special attention to harvest intervals listed on the label.

The ravenous caterpillars will not kill your tree. Over a period of several years, the defoliation will add stress, which, combined with poor soil, root competition and other challenging environmental factors, is likely to result in a slow death for the plant. Perennial flowers will not suffer as long, but also are unlikely to die from one late season defoliation.

If the caterpillars have already come and gone, water what is left of your plants to help them out in hot days ahead. Remember to water deeply and infrequently for best results.

For those of you who have yet to see a caterpillar defoliating any of your trees or flowers, more are on the way. They are hairy, too.

Douglas County Extension Master Gardeners can assist with insect identification or other garden questions from 1 p.m.-4 p.m., Monday-Friday at 843-7058 or dgemg@sunflower.com.

- Jennifer Smith is the Douglas County Extension AgentHorticulture for K-State Research & Extension. She can be reached at 843-7058 or <a href="mailto:smithjen@ksu.edu">smithjen@ksu.edu</a>.

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