Extension News

Ask the ISU Garden Experts: Twig Beetles, Hostas and Magnolias

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


Small, brown, leafy twigs are falling from my oak tree. What could be the problem?

The twig girdler is probably responsible for the falling twigs if the twigs appear as if they were neatly cut from the tree with a pruning shears. The twig girdler is a long-horned beetle about three-fourths of an inch long, stout, grayish-brown with a lighter colored band across its wings. The antennae are as long as the body.

Adult beetles typically begin to emerge in mid-August and continue through early October. The adult female chews a neat, V-shaped groove around and partly through the small twig. This leaves the twig attached to the tree by a thin center core of wood. The beetle then deposits an egg in the bark of the twig section beyond the cut. The portion of the twig beyond the cut dies quickly and falls to the ground because of wind or its own weight.

The egg within each fallen twig hatches into a tiny larva that bores into the dead twig to feed. The small larva stays inside the fallen twig through the winter and resumes feeding and consumes most of the wood the following spring. New adult beetles emerge late the following summer and early fall. There is only one generation a year.

Common hosts of the twig girdler include oak, hickory, honeylocust, hackberry, linden, redbud, and various other shade and fruit trees.

Fortunately, twig girdlers do not cause serious harm to healthy, well-established trees. Collect and destroy dropped twigs as they appear on the ground. Insecticides are not necessary (nor effective) in home landscape situations.

Do hostas need winter protection?

Most hostas do not need winter protection if they have been in the ground for at least one full growing season. However, a winter mulch is often beneficial to hostas planted in late summer or early fall. Repeated freezing and thawing of the soil in the winter months may heave recently planted hostas out of the ground, causing serious damage. Applying several inches of clean, weed-free straw, pine needles, or other mulch in mid to late November should provide adequate winter protection.

My saucer magnolia has produced several fruit. How do I germinate the seeds?

The bright reddish orange seeds of the saucer magnolia need to be exposed to cool, moist conditions before they will germinate. This can be accomplished by planting the seeds outdoors in fall. Plant the seeds 1/4 to 1/2 inch deep. The cool, moist conditions in the soil during the winter months will eventually break the magnolia seed’s dormancy, allowing the seeds to germinate in spring.

The cool, moist requirement can also be attained indoors. Place a layer of moist peat moss in the bottom of a small coffee can or similar container. Place the magnolia seeds on the moist peat, then cover the seeds with additional moist material. Punch 2 or 3 holes in the plastic lid and then place it on the container. Place the container in the refrigerator for 3 to 5 months. Afterwards, remove the seeds from the refrigerator and plant indoors. The magnolia seeds should germinate in a few weeks. The magnolia seedlings can be moved outdoors in spring.

Since there are inherent dangers in planting seeds outdoors in fall (for example, squirrels or other small animals might eat the magnolia seeds), starting the seeds indoors would probably be the best option.


Contacts :

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

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