Will corn hold up under yield pressure?

  • corn yield predictions

    The USDA acreage report shocked markets by claiming 100,000 more corn acres than expected. "While guessing at crop prospects before we see many tassels is always a little dangerous, we now have some idea about the physiological state of the crop as it enters the most critical yield-determining part of the season," said Emerson Nafziger, University of Illinois Extension agronomist.

  • silking

    The latest National Agricultural Statistics Service reported 8% of Illinois corn crop is silking as of July 3, behind the 21% average the past 5 years. But corn planted in early May is set to silk this week "at about 1,300 or 1,350 growing degree days," Nafziger said.

  • wet fields

    It's no secret that wet weather is behind slower maturity: "The corn crop has been planted and replanted. Most of it looks fair, some looks good and some looks like crap. In some instances it is in the same field," Illinois farmer Kelly Robertson said on his blog. "I am pretty sure that it won't be a bumper crop if appearance has anything to do with it. When it quits raining this crop is going to suffer with no or shallow root systems."

  • drying fields

    Many IL fields are beginning to dry out after 2 weeks of dry weather and sunshine. "Root systems have grown well, and the good rate of crop growth shows that roots are trapping soil water beneath the top few inches," Nafziger said. "Now that the surface soils are drying out, roots are actively taking up water from deeper in the soil, and this is keeping the plant functioning well."

  • N deficiencies

    Fields that haven't bounced back may have N deficiencies. Crop Talk's Nebrfarmr has a solution: "From my experience, too much rain pushes any N already applied deeper in the soil... doesn't encourage the corn to send roots down. Applying something to the surface or very shallow will help." Applying dry N, even as late as waist-high, is "well worth the expense."

  • Photosynthetic rates

    Regardless of height, the majority of corn is a health dark green in color, signaling "photosynthetic rates are high, and as leaf area and light interception approach their maximum, the crop is producing sugars at maximum rates," Nafziger said. "This is exactly what the crop needs to do as it enters the pollination stages."

  • Browning

    A likely hot and dry July can turn things brown and indicate a drop in kernel numbers and yield potential. Nafziger says the main things to watch for now are signs that photosynthetic rates might be dropping, and, by the time pollination ends and silks start to turn brown, how many kernels have been fertilized.

  • Leaf symptoms

    Threats to photosynthetic rates are almost always visible as leaf symptoms, Nafziger said. Look for:

    • - Loss of dark green color
    • - Curling up due to lack of water
    • - Disease damage to leaf
    • - Loss of leaf area from hail or insects
  • Looking ahead

    Looking ahead: after silks turn brown, it should be easy to see which kernels are fertilized and increasing in size. After 2 weeks of brown silks, any abortion is rare, Nafziger said. Maximum yield potential occurs when kernel numbers are around 15 to 20 million per acre.

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