Extension News

Ask the ISU Extension Garden Experts: Lace Bugs, Bell Peppers and Tomato Hornworms

Note to media editors: Got gardening questions? Call the Hortline at (515) 294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or e-mail us at hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, http://www.yardandgarden.extension.iastate.edu

8/6/2009

Why are the leaves on my hackberry turning brown and falling to the ground?

The browning of the hackberry (Celtis occidentalis) leaves is probably due to lace bugs. Lace bugs are sap feeding insects commonly found on the leaves of shade and ornamental trees in Iowa. Trees most commonly affected are hackberry, sycamore and oak. Adult lace bugs have attractive wings that are beautifully sculptured with an intricate pattern of veins resembling lace, hence the common name.

Lace bugs feed on the underside of the leaves. They pierce the leaf epidermis with their sucking mouthparts and cause the characteristic pale yellow, scorched or “bleached” discoloration on the upper leaf surfaces. The underside of heavily infested leaves will be speckled with small, black, shiny “varnish spots” (excrement). While lace bugs are present throughout the summer, damage symptoms usually don’t develop until August or September.

Lace bug damage varies greatly from year to year, mainly in response to variations in natural controls and weather conditions. Severe feeding may cause premature leaf drop, but healthy, well-established trees are not seriously harmed. Spraying infested trees with an insecticide in late summer is of little or no benefit to the trees. Further, spraying when it is too late for effective control may cause more harm than good by killing the insect’s natural enemies.

When should I harvest my bell peppers?

Bell peppers are usually harvested when large, firm and dark green (immature stage). They may also be allowed to fully ripen to red, yellow, orange, or other colors. Fully mature bell peppers are slightly sweeter and contain higher amounts of vitamins than immature green fruit.

There are large, green caterpillars on my tomato plants. What should I do?

The large, green caterpillars are probably tomato hornworms. Tomato hornworms are bright green, up to four to five inches long and have red or black, horn-like projections on their rear ends. After feeding, hornworms move to the soil where they pupate and spend the winter. The following summer the pupae transform into five-spotted hawk moths and start the cycle over.

Tomato hornworms feed on the leaves and fruit of tomatoes and other vegetables including eggplant, potatoes and peppers. They can quickly defoliate portions of the plant and heavily damage the fruit.

Often the best control option for home gardeners is to simply pick the caterpillars off by hand and destroy them. Another control option is to use a biological insecticide, such as Bacillus thuringiensis (Bt), or a synthetic home garden insecticide. As always, carefully read and follow label directions when using pesticides.

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Contacts :

Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu

Del Marks, Extension Communications and External Relations, (515) 294-9807, delmarks@iastate.edu