Some Nebraska producers are deciding whether to replant their crop or plant another crop after severe storms damaged fields and reduced stands this week.

Some fields suffered so much damage from heavy rains or hail that tillage or another operation will be needed to fill in the washouts before replanting. With minor soil erosion, sweep tillage will maintain much of the crop residue. In many other situations you'll need to move so much soil that all the crop residue will be destroyed, leaving the soil more susceptible to wind and water erosion.

The next two sections on assessing early season hail damage on corn and the effect of stand loss on corn yields are by Kraig Roozeboom, Crop Production and Cropping Systems Specialist at Kansas State University.

Assessing Early Season Hail Damage on Corn

Hail damage always makes corn look bad and can make for some sleepless nights. While the physical damage is apparent, the actual effect on yield is not as obvious. As the crop gets more mature, potential corn yield losses from hail increase, up to the silk stage, when peak yield loss occurs. After silking, yield losses from hail damage normally decline.

Why? There are several reasons, and all are based on the growth and development of the corn plant.

• Emergence until stem elongation (VE to V5). Up through the 5-leaf stage of growth, the growing point of corn is below the soil surface. At the worst, hail damage would remove all five leaves, but typically not damage the growing point. A corn plant has 24 to 26 leaves at tasseling. If the plant loses five of those leaves early on, it will still have the potential to have 19 to 21 leaves at tasseling. Yield will be reduced but much less than one might expect from the appearance of the plant.
• Stem elongation to tassel (V6 to VT). The growing point begins extending aboveground by the 6-leaf stage, although it is still protected by several layers of leaves and sheaths. The number of rows that will be in the ear is established by the 12-leaf stage. Stress during V8 to V11 can reduce row number. The number of kernels per row is not determined until about V17, just before tasseling. Hail damage and loss of leaf area during these stages of growth can cause increasing potential for yield loss. Hail can also cause stalk bruising during these stages of growth, but it is hard to determine the amount of damage from stalk bruising until later in the season.
• Tassel to maturity (VT to R6). At VT to R1 (tassel to silk), the corn plant is more vulnerable to hail damage than at any other stage. The tassel and all leaves are exposed at that time. No more leaves will be developed, and the corn cannot replace a damaged tassel. Furthermore, the stalk is exposed, with only one layer of leaf sheath protecting it. Unlike wheat, corn cannot fill from the stem if leaves are lost at this stage of growth. The six to eight leaves above the ear are the most important, and provide most of the grain fill.

The four-week period centered around silking is critical to corn, and not only in regard to hail damage. Drought stress, excessive moisture, extreme heat, diseases, and even high winds can all stress the plant at this critical growth stage and reduce yields. Early in this period, stress can reduce kernel number by limiting potential ear size. Stress right at silking can reduce the number of kernels fertilized. And stress just after silking can cause fertilized kernels to abort.

Effect Of Stand Loss On Corn Yields

Stand loss usually causes relatively little yield loss, at least at populations greater than 24,000. The amount of yield reduction from stand loss depends on the growth stage.

Research by Barney Gordon, agronomist at the KSU North Central Experiment Field, evaluated the effect of stand loss on yields, ear number, and ear size by removing plants at various stages of growth. This study showed that:

• Yield loss was much less than stand loss at every growth stage.
• Yield loss increased with stand losses that occurred at later growth stages.
• Ear number per plant increased slightly at 50% stand loss, and more at 75% stand loss.
• Seed weight did not change as a result of stand loss (data not shown)
• Ear size increased with greater stand loss at early stages of growth.

When considering replanting due to poor stands, remember that planting corn in early June in much of Kansas can result in yield losses of up to 50% compared to a typical planting date. Based on the data above, it would probably be better to keep an existing stand even with as much as 50% stand loss than to replant in early June. Of course, much depends on the uniformity of the remaining stand and the weather for the rest of the growing season.

Other Factors in Your Replant Decision

Also consider such factors as weed management, diseases and insects, and how the crop will be affected by the storm damage. If the crop is herbicide-tolerant, this helps manage weeds with reduced crop competition as a result of reduced plant populations, skips, delayed crop canopy, etc. Insect problems can increase, especially in non Bt hybrids, with delayed plant growth. Disease problems also are likely to increase in damaged corn plants.

If the damage to the corn crop was enough to consider replanting or planting to another crop, be aware of potential problems. If the damaged crop was Roundup Ready corn, be sure the previous crop is destroyed or volunteer corn could become a major problem. (See story in this week's CropWatch.) If the corn crop was conventional and Roundup Ready corn or Roundup Ready soybeans are being planted, controlling the previous crop will be easy.

If Roundup Ready soybeans are to be planted after Roundup Ready corn and the corn was more than 18 inches tall when damaged, treatments such as Fusion or Select may not adequately control the regrowth.Both soybeans and grain sorghum can be planted later than corn without giving up as much yield. Some growers can use Lumax for weed control in grain sorghum. Check label.Before replanting or selecting another crop, always check for replant options and rotation restrictions for any herbicide that may have been used on the field.

What is the yield potential for late planted corn? In 1992 agronomist Paul Nordquist conducted research at UNL's West Central Research and Education Center at North Platte on this topics. The results are in Table 1.

Bob Klein
Extension Western Nebraska Crops Specialist
with
Kraig Roozeboom
Kansas State University Crop Production and Cropping Systems Specialist
Barney Gordon
KSU Agronomist at the North Central Experiment Field

June 12, 2009