July 11, 1997

Dutch Elm Disease

We have been receiving samples of elms with Dutch elm disease (DED). Several people around the state also called the ISU Plant Disease Clinic about elms that are not doing well. The symptoms described include wilting or flagging of one or more of the upper branches and/or general wilting, yellowing, and browning of leaves. Others have trees that have died a few weeks after they first notice the problem.

Earwigs: Another Accidental Invader

Earwigs are a fairly well known insect, from folklore if not from actual experience. The earwig is the insect reputed in superstition to purposefully crawl into the ears of sleeping persons, and from there bore into the brain. Of course, there is no truth to these tales.

Earwigs are fairly common, though not often abundant in Iowa. They are rarely noticed except after prolonged periods of a year or more with wet weather.

Harvesting Sweet Corn

Harvesting sweet corn at the proper stage of maturity is essential to insure a high quality crop.

Sweet corn should be harvested at the milk stage. At this stage the silks are brown and dry at the ear tip. When punctured with a thumbnail, the soft kernels produce a milky juice. Over- mature sweet corn is tough and doughy. An immature ear will not be completely filled to the tip and the kernels produce a clear, watery liquid when punctured.

Pinpointing the Problem with Pin Oak

Here's a commonly heard problem on the ISU Hortline: "I have a beautiful pin oak in the front yard--it's been there for almost 25 years. And now it's starting to die off and the leaves look terrible. What can I do?"

On most Iowa soils, probably the best course of action would have been to never have planted pin oak in the first place. While this homeowner thought they were planting for posterity, what they really planted was a problem tree that will cost them significant headaches for the life of the tree.

Mid-summer Rose Care

Roses are popular garden plants that provide season-long beauty. However, they also require season-long attention. Adequate water during dry periods is essential for continuous bloom. Roses require at least an inch of water per week. A good mulch layer around the plants will help retain soil moisture. Water roses early in the day and avoid wetting the foliage. Black spot, a serious foliage disease of roses, is spread by water splashing on the leaves.