As we wind ourselves through the dog days of summer, I thought a summary of agronomic opportunities in corn would be good to review.
1.) Pollination: The most critical 5 - 8 days of your corn plants life. At this point the corn plant stops developing more leaves and root mass has primarily established. Stresses endured during this time period and beyond directly impact final yield.
a.) Most corn pollination takes place mid-morning to early afternoon, when conditions are dry and before the hottest portion of the day.
b.) An average ear has between 750-1000 silks. Each tassel can produce between 3-5 million pollen grains- more than enough to limit pollination issues under normal growing conditions.
c.) Within 2-3 days of when fertilization, the silk will detach itself from the newly formed kernel.
d.) If you wish to check on pollination, gently remove an ear from the plant and carefully remove the husk. Try not to remove silks at this time. Once husks are removed, gently shake the ear and let silks fall away. All pollinated kernels will lose the silks any unfertilized kernels will keep silks attached.
2. Ear Rots: Hot-wet conditions at silking and up to 3 weeks following pollination are ideal for developing ear molds such as:
a.) Gibberella ear rot - Typically is diagnosed when pink to red mold is found at the tip of the ear and works its way to the base.
b.) Diplodia ear rot - Is identifiable by a white to gray mold that covers the ear. Resulting in light weight ears.
c.) Fusarium ear rot - Is recognized by clusters of white to gray kernels or individual kernels and by a starburst or fine red lines radiating from the point of silk attachment.
3.) Stalk Rots: Generally start to appear from mid-August through harvest. Identification of fields with stalk rot issues will be necessary to figure out a sound harvest strategy. Here are some common stalk rots and how to determine which is which.
a.) Gibberella stalk rot - Infection occurs after pollination. Favored by warm/wet weather. Vascular bundles appear reddish in color.
b.) Anthracnose stalk rot - Symptoms usually apparent just prior to physiological maturity or "Black layer" corn. Shiny black blotches appear on outer stalk. Inner stalk pith can also become infected and turn black. Generally results in plant dying near the ear and lodging.
c.) Diplodia stalk rot - Very similar to Gibberella, but without the reddish color. Infection site is lower portion of stalk near root crown. Tiny black specks embedded in rind of stalk are visual identification tools. Tends to be more predominant in continuous corn fields, as pathogen overwinters in residue.
4.) Fungal Diseases: We have reviewed these in previous scouting updates. The big three I would continue to keep a vigilant eye out for are:
a.) Gray Leaf Spot (GLS)- Rectangular shaped lesions that have gray/necrotic appearance. Early identification is crucial for maximum effectiveness of fungicide. Disease can infect from silking through maturity. Extended periods of high humidity or wet weather encourage disease development.
b.) Northern Corn Leaf Blight (NCLB)- Large cigar shaped lesions are gray to green in color. Size of lesions is determined by different resistance genes in corn plant. Usual infection occurs at or shortly after silking. Long periods of leaf surface moisture favor development. This disease has become more predominant over the past several years.
c.) Southern Rust - Overwinters in Southern US, but spreads into Midwest though weather patterns. Cinnamon brown pustules are scattered on upper leaf surfaces. Need a systemic fungicide to treat.
As fields continue to dry out and roots regain their ability to absorb needed nutrients, I have seen a gradual improvement across the sales territories. I'm not predicting biblical style recoveries by any means, but in general corn fields have started to develop a more desirable color and uniformity. Applying late season nitrogen doesn't always correlate to improved yields. Primary yield factors were determined at V6-8 (ear girth) and V12-15 (ear length) depending on hybrid.
Make sure that you continue to walk your fields over the next several weeks as pollination wraps up to get a better idea of what this fall might hold in store.
Until next time,
Sean D. Jordal