Sunday, September 7, 2014

Time to Evaluate Corn Stalk Quality

After this growing season, there are many concerned that there could be some issues with corn root lodging or stalk lodging.  Often times, if early corn growing conditions consist of high amounts of moisture or nitrogen (no stress before pollination), which most likely increases the production of grain (higher yields), but later in the growing season (post pollination), there are factors (discussed below) that hinder corn photosynthesis, which can hinder the flow of sugars to grain. Sugars can then be taken from the stalk, which could predispose the corn plant to be infected by stalk rot pathogens.   

It is very, important to evaluate corn now.  Begin by evaluating the stalks of your earlier maturing corn hybrids and continue to scout your later maturing corn hybrids. Corn plants that consist of stalk rot, will senesce early.  The lower part of the stalk will turn brown.

1.) Scout an entire field for stalk quality, not just field edges
2.) Be sure to sample areas that may have different soil types, soil drainage patterns, hybrids, rainfall, and fertility - as these all could be factors that could factor into stalk quality
3.) Check 10 plants in several (4 to 5) areas of a field.
  • First, pinch the second or third internode above ground level - if a stalk collapses easily, cut open the stalk and check for signs of disease or insects.
  • Second, push on corn stalks - if they break, they could be more susceptible to stalk lodging.
4.)  Try to solve the problem and decide whether if it is just an area, one field, or if all fields appear to have stalk quality issues.
5.)  If more than 10% of stalks appear to be compromised, harvest these areas as soon as grain is physically mature, with a slower combine speed.

What can causes corn root or stalk lodging:
1.)  Weather - Depending on soil type, amount of soil moisture, and root development, corn hybrids can be blown over during a wind event. However, some strong winds can overcome the best root development.  Corn damaged due to weather can be more susceptible to disease and infection of stalk rot pathogens at points of injury on the stalk. For example, if hail occurs after pollination, stalk rot is almost always inevitable.
Hail injury to corn - can hinder stalk quality due to mechanical injury and may be more susceptible to stalk rot pathogens
Wind injury to corn - lower stalk remains green/ no rot is present  (picture taken by Stephanie Porter)
2.)  Insect - corn rootworm larvae can feed on roots and cause root lodging.  European corn borer (ECB) (usually the 2nd generation) can tunnel into the corn ear shank and cause ear dropping or tunnel into the stalk and cause stalk lodging.  Of course, ECB injury is more often found on corn hybrids without GM traits to help suppress or control the ECB. Often times, if there is ECB injury above the ear, stalk rot can ensue.
ECB larvae - 2nd generation found feeding near ear shank.

ECB feeding and frass found near corn ear shank.

Corn turn red if there is ECB feeding above the ear.  This red color shows that the plant's sugar movement is inhibited.

ECB feeding within a corn stalk.

Corn rootworm feeding on corn roots (Picture taken by Matt Montgomery)
3.)  Disease - there are several stalk rot pathogens (usually fungal) that can infect corn roots or injured areas of the stalk. Research has indicated that high incidences of foliar disease (gray leaf spot and northern corn leaf blight) may predispose corn to stalk rot.
"Carl Bradley, University of Illinois plant pathologist and author of the Illinois study, says when a foliar disease such as gray leaf spot is present, the blighted leaves are unable to produce enough photosynthetic activity to fill the ear. The plant may rob the stalk of the sugars needed, a process that can damage the stalk and allow pathogens to take hold. If a grower has severe gray leaf spot and does not apply a fungicide in-season, there is a good chance he will see stalk rot in those plants later in the season."
Anthracnose stalk rot pathogen infected an injured area of stalk due to wind injury - found earlier in the season - further compromises stalk after wind event

Stalk infected with Diplodia stalk rot pathogen - found later in the season - causes stalks to break at infected internode
4.)  STRESS - can cause corn to be prone to stalk rot
a.) High plant populations -increases plant competition for light and could reduced stalk diameter.
b.) Extremes in soil moisture -root rot or compromised roots due to lack of oxygen
c.) Nutrient deficiencies or imbalances-we are especially concerned with nitrogen loss this year.  If corn plants are without adequate levels of nitrogen, they could be less vigorous and put all their energy into grain development; therefore, stalks could be compromised and more likely to be infected by stalk rot pathogens and lodging.  On the flip side, corn growing within higher nitrogen levels (promotes lush foliage growth) along with low levels of potassium (encourages premature stalk death) can also cause corn to be more prone to stalk rot or lodging.
d.) Cloudy weather - late season cloudy weather may not provide enough photosynthesis (decrease photosynthetic rate) to keep ears alive.
e.) Drought - If the drought threshold of corn is reached, this could cause a drastic reduction in photosynthesis.  Irrigation should not be reduced during grain fill.
e.) Cropping sequence -a corn on corn rotation may be more at risk when it comes to lodging
f.) Taller ears on corn hybrids or hybrid stalk strength could also be factors when it comes to stalk quality, but be sure to research all the other possibilities listed above.

Corn accidentally planted at 60,000 plants per acre - too high of a plant population - increased plant competition and reduced stalk diameter caused these plants to be lodged during a wind event.
Firing of lower leaves because of nitrogen loss - in some cases, plant may rob the stalk of the sugars needed and damage the stalk quality
The longer that corn is left in the field, the greater the risk for root or stalk lodging due to wind, insects, disease, or other factors.

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