October 15, 2020
Fall is upon us, and every year, agronomists get calls about downed corn. In general, poor late-season standability is often attributed to one of the following issues: weather, genetics, diseases, physiological processes in the plant or nutrient deficiency.
Weather: The main weather issue leading to poor late-season standability is wind events. While some weather events like the derecho (hurricane-level winds seen in Iowa this year) are an obvious cause of downed corn, other issues may occur during the season and go unnoticed until harvest unless an aerial image is gathered during the growing season. Often, other things have led to weakened roots such as corn rootworm feeding, compaction, excessive early season rain which leads to shallow rooting depth, or saturated soils that can’t hold roots in place during a wind event.
Product genetics: Each product has genetic ratings for root and stalk lodging. These ratings indicate the likelihood of late-season issues. Other ratings to consider are ratings for stalk rots such as anthracnose. Choosing products with better ratings for these categories can help provide additional protection.
Diseases: Stalk rot occurs almost every year in the Midwest. As the stalk becomes weaker because of diseased tissue, the plants become more susceptible to late-season standability. A few of the most common stalk rots are anthracnose, Diplodia and Gibberella. Physoderma node breakage, a relatively new disease in the Midwest, has been a factor in recent years. Physiological stalk rot is not caused by disease; however, it can occur when environmental conditions are unfavorable.
Anthracnose stalk rot (ASR) is one of the most common stalk rots across the Midwest. The lower stalk features black splotches on the bottom couple of internodes. Upon splitting the stalk, it is often rotted and hollow. If it occurs early in the season, it can cause a light-pink ghosting on the leaves. Our breeding program has increased screening efforts for ASR, and seed guides now contain ratings for this disease.
Figure 1. Anthracnose stalk rot.
Diplodia stalk rot causes a black dotted appearance on the lower internodes and hollowing of interior tissue. The black splotches are embedded in the stalk and cannot be scrapped off.
Figure 2. Diplodia stalk rot.
Gibberella stalk rot has a pink hue to it when splitting stalks. This is a distinctive coloring that only appears with Gibberella stalk rot.
Figure 3. Gibberella stalk rot.
Physoderma node breakage is relatively new within the past five years or so. Instead of the typical hollowing out of the stalk by the fungi, physoderma feeds on the “rind” of the stalk and weakens the outside of the stalk. Depending on how severe the infection is, it can lead to the stalk “popping” when pushed by wind or mechanical means and can break clean off at one of the first nodes above the ground.
Figure 4. Physoderma node breakage can cause stalks to snap at lower internodes.
One of the most common reasons for standability issues in the fall can be related to the physiological process of the plant repurposing carbohydrates in the stalk and using them to fill the ear. In years when kernel sink is high, nutrients have been lost, rainfall is reduced during grain fill, or a corn product with high yield potential is used, these symptoms can be found without the presence of any disease
Figure 5. Physiological stalk rot.
Nutrient Deficiencies: Nutrient deficiency ties in to physiological stalk rot. Anytime the availability of the macronutrients, nitrogen, phosphorus or potassium is reduced, the plant can pull these from the plant to fill the ear. The lower leaves tend to die faster than normal in these cases. This can lead to a hollowing out of the stalk, and a wind event can result in standability issues.
Regardless of what caused weakened stalks, pre-harvest scouting is one of the best ways a farmer can assess stalk strength and determine the best order for harvest. Corn products with higher moisture content with weakened stalks may need to be harvested ahead of drier products to help reduce harvest difficulties and help preserve yield.
Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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