Corn responding well to warmer temperatures

After a relatively cool start to the growing season, warmer temperatures have prevailed for the past couple of weeks and the corn crop has responded favorably. Needless to say, there have been numerous early season maladies that have raised concerns about the potential of this year's crop.

Uneven corn

Uneven corn.

This has been a widespread concern across the state. There are many causes for uneven corn and, in most cases, it cannot be linked to any one reason. Generally, uneven corn is caused by several things that interact to produce one large effect. Compaction, shallow planting, dry topsoil, cool temperatures, and anhydrous ammonia burn all are factors in stunted growth this year, and herbicide interactions cannot be ruled out as a potential cause, either. As temperatures warm and rainfall is received, growth will resume and the unevenness will slowly disappear. Be aware, however, that as larger plants continue to grow, they may fill in for the smaller plants, giving the appearance that things have returned to normal when in actuality they have not.

Purple corn

Purple corn is generally related to stress and restricted root development.

This is another widespread concern across the state. Like uneven corn, the causes of this malady are numerous. Although purple coloring is a characteristic of some hybrids, in general it is related to stress and restricted root development. Cool soils, compaction, dry soils, and shallow planting all may impact root development and result in the purple color on leaves. As the stress is relieved and roots resume growth, the symptoms generally disappear.

Striped corn

Striped corn may be linked to stress from environmental conditions.

As with purple corn, striped corn may be related to hybrid characteristics. In addition, however, it can be linked to stress from early-season environmental conditions. Striping may result from warm temperatures that trigger rapid growth after a cool period with relatively slow growth. Again, the condition is noticeable early but disappears as the plants grow. Nutrient deficiencies that would cause such symptoms are rare to nonexistent in Iowa and generally are found on soils with a fairly high pH.

Hail damage

Hail damage to corn.

The stage of development when hail damages a crop is critical in determining potential losses. For young corn plants (V5 or younger), actual losses will be minimal. Leaves that are exposed at this point are small, they generally fall off the plant soon, and thus contribute little to overall yield. Additionally, the growing point of the corn plant at this stage is protected below ground. For corn plants at V6 or larger, leaf tissue loss begins to be a factor in determining yield potential. Likewise, the growing point has now risen above the soil surface and is susceptible to damage. Actual stand losses can impact yield potential significantly. Allow the plants time to recover before making hasty decisions to replant or destroy the stand. Regrowth should be evident in one to three days.

The corn plant is growing rapidly now and will continue to do so provided temperatures are warm and moisture is plentiful. The corn plant will tolerate temperatures into the mid-90s provided there is ample moisture. Recent rains have helped recharge subsoil moisture levels that will be beneficial as the crop advances toward pollination.

This article originally appeared on pages 132-133 of the IC-478(16) -- July 7, 1997 issue.

Updated 07/06/1997 - 1:00pm