The Liqui-Grow locations and surrounding vicinity in east-central and southeast IA—as well as those in northwest IL—have experienced above normal precipitation in the 2015 growing season. Precipitation ranged from about 19-to-28 inches for the period from May 1 through August 25, with most of this precipitation falling in June and July. This excess precipitation has caused severe nitrogen loss in some places/fields, and has provided good conditions for foliar diseases.
Does this mean stalk and root rots will be a concern for the 2015 harvest?
- Nitrogen loss from excessive spring precipitation and foliar diseases has resulted in season-long photosynthetic stress in some geographies/fields.
- The prolonged stress means carbohydrate reserves (sugar) will be low. Thus, intense competition will occur during grain fill between the developing ear, stalks, and leaves.
- The ear is almost always the bigger “sink” for carbohydrates.
- Therefore, stalks will be left without the needed energy to fight invading pathogens.
- Unabated pathogen invasion means stalk rots will be likely in 2015.
- Stalk rots stop grain fill prematurely and result in lodged plants making the harvest of all sellable grain difficult, and can reduce grain quality.
- Management options at this juncture are few: scout and harvest severely infected fields, first, when possible.
- Managing for good yields (reducing season long photosynthetic stress) usually reduces the risk of stalk lodging.
The right conditions for stalk rot in 2015
Most corn fields I have been in as of late are just entering, or are approaching mid-R5 (dent). Meaning grain weight is still rapidly accumulating and black layer (physiological maturity) is 3-to-4 weeks off. Even then, harvest is drawing ever near, and we begin to wonder what surprises it may bring.
One surprise could be stalk lodged corn. Why do we reach this conclusion? Well, we believe a significant amount of photosynthetic stress—reducing sugar supply from what it could have been—during prolonged periods of the growing season is a major contributing factor to stalk rots.
So, did we have enough stress for long enough in 2015? The answer is, yes where we had nitrogen loss or a significant amount of foliar diseases, and a big YES when both were present.
The compromised canopy—and ability to conduct photosynthesis—means there will be intense competition for carbohydrates between the remaining leaf area, stalks, and developing ear. Given the ear is almost always the dominate sink for sugars (we hope), the ear typically wins this battle.
Because carbohydrates are remobilized from the stalks and lower leafs, this results in less cellular energy to regulate functions—like thickening cell walls to stop further fungal invasion. This reduction in the ability of the lower stalk to defend itself means whatever stalk rot pathogen is present in the largest abundance will have free reign on the energy rich pith.
Profit loss and stalk rots
Stalk rots reduce profitability in 3 ways: early senescence (stopping grain fill prematurely), the physical inability to pick up all harvestable ears, and dockage from ear rots that may develop from ears physically laying on the soil surface.
The environment in 2015 will favor the development of Anthracnose, Gibberella, and Diplodia stalk rots, however others are surely possible.
How to spot stalk rots
While walking fields this time of year, be looking for symptoms of stalk rots. These can range from plants that have senesced prematurely (Picture 1), top die back, lodged plants (Picture 2), and those with lower stalks that have a brown instead of healthy green rinds (Picture 3).
While other biotic and abiotic factors can cause symptoms that resemble those of stalk rots, splitting and inspecting the lower stalk and roots can help narrow down the true problem.
If stalk rots are present, some pith is often missing, causing cavernous voids in the inner stalk. In most cases, the inner pith and nodes will be discolored—black to brown, or even a red tinge, it depends on the specific stalk rot pathogen. This is particularly apparent when compared to healthy stalks (Picture 4).
In addition, stalk rots are commonly associated with root rot. In fact, stalk rots often start in the roots and move into the lower stalk.
Tips for managing stalk rots
At this point, the management options are few, other than inspecting fields for stalk rots and scheduling them for harvest as soon as practically possible. The good news is that most management tactics are aimed at producing good yields. So, ones that minimize photosynthetic stress will reduce the likelihood of stalk rots.
- Avoid continuous corn when possible.
- Use foliar fungicides when necessary to control foliar diseases.
- Use a nitrification inhibitor (Instinct II) in environments where you expect nitrogen loss.
- Don’t plant unnecessarily high plant populations.
- Avoid hybrids with poor stalk strength or low stalk rot ratings.
- Maintain good potassium fertility because potassium is associated with stalk rigidity.
Corn plant that senesced and stopped grain fill
prematurely, notice the dropping ear. Inspection of the lower
stalk revealed what appears to be Anthracnose stalk rot.
Lodged stalk between two healthy stalks. Notice
the lodged stalk is pinched, further inspection revelded little
pith in the inner stalk, leaving only the rein for support.
Plants with stalk rot will often have a brown
discolored lower stalk, and is typically isolated to the lower few
nodes (center plant).
Inspecting the lower stalk of plants expressing symptoms
of stalk rots often reveals cavernous voids (tip of pocket knife) were
the pith has completely deteriorated. Plants with stalk rot will often
have discolored (bottom plant) lower stalks, the pith of healthy stalks
should be bright white. This plant has what I believe to be
Anthracnose stalk rot.
Nielsen, R.L. 2013. Stress during grain fill: a harbinger of stalk health problems. Purdue Univ.
https://www.agry.purdue.edu/ext/corn/news/timeless/stalkhealth.html. (accessed 25 Aug 2015).
Tamra, A.J., J.M. Rees, and R.M. Harveson. Common stalk rot diseases of corn. Univ. of Nebraska. http://ianrpubs.unl.edu/live/ec1898/build/ec1898.pdf. (accessed 25 Aug 2015)
Pataky, J.K., 2000. Fungal Stalk Rots. In: D.G. White. Compendium of corn diseases. American Phytopathological Society, St. Paul, MN. p. 38-43.