September 1, 2022
As the season pushes along and corn enters the reproductive stages, so begins one of the most rewarding and valuable times to scout and evaluate fields. Ear development and grain fill allow agronomists and growers to see what yields might be and possibly identify areas of concern. Sometimes, as we push later into the season, we see ears hanging low prematurely.
Corn ears typically remain upright until they have reached physiological maturity or “black layer.” At black layer, the shank which supports the ear begins to deteriorate and causes the ear to droop. Drooping serves a purpose as it allows moisture to run off and onto the ground instead of entering and accumulating in the husk of an upright ear. However, sometimes ears droop prematurely, even as early as the dough to dent stages. Heat, drought, and environmental stress are factors that can cause premature ear droop.
Stress is one key factor that can cause ears to decline prematurely. This can happen when the crop experiences adequate conditions early in the season and into pollination. When stress conditions occur in the early and later grain fill periods, the plant can begin to shut down, and at times cannibalizes water and nutrients from the stalk and even the ear shank to continue to fill the ear. This can cause premature maturation and ears to droop earlier than expected (Figure 1). Other stresses such as high weed pressure can compound the heat and drought stress.
Figure 1. Premature ear droop caused by stress.
Disease
Corn diseases such as Goss’s Wilt, Fusarium Crown Rot, Anthracnose, and Tar Spot can also be a key. Stalk, root, and foliar corn diseases can cause the plant to shut down and cause the ears to droop prematurely.
The severity of the disease will dictate how it impacts the plant. In 2021, some areas had a high incidence of Fusarium Crown Rot which is favored by cool, wet conditions early followed by hot, dry conditions in mid-late June. The disease caused the vascular tissue of plants to deteriorate which forced to plants to redistribute water and nutrients from the stalk to the ear causing plants to mature too quickly (Figure 2).
Figure 2. Premature plant death and ear droop caused by Fusarium Crown Rot.
Insects
Another often overlooked cause of premature ear droop could be European Corn Borer. Typically, most corn products today have Bacillus thuringiensis (Bt) protection from European corn borer but because of either marketing advantages or grower preference there may be fields that are conventional or organic. Second generation European corn borer can feed on the ear shank, weakening it, and causing the ear to droop early (Figure 3).
Figure 3. European corn borer feeding in ear shank.
Associated Yield Loss from Premature Ear Droop
Potential yield loss varies depending on the severity of and timing of when ears prematurely droop. If ears droop during early dent and the shank is pinched off, shutting off the flow of carbohydrates to the ear, severe yield loss could be expected. If ears don’t droop until the end of dent stage when the milk line is closer to the tip of the kernel, potential yield loss is likely to be much less.
Another factor to consider when ears prematurely droop is the possibility of ears dropping to the ground because the integrity of the shank is reduced. Windy conditions can increase the risk of ear drop and harvest loss. Fields should be scouted pre-harvest to determine shank integrity and help determine if certain fields should be prioritized for harvest.
Scouting fields throughout the season is the key factor to help determine if and why ears are drooping prematurely. Stresses such as heat, drought, insects, and disease can all contribute and may all be present in a field. Continue to scout fields up to harvest to help ensure potential yield losses are kept to a minimum.
Sources
Nielsen, R.L. (Bob). 2020. Do your ears hang low? (Premature ear declination in corn). Corny News Network. The Chat ‘n Chew Café. Purdue University. http://www.kingcorn.org/news/timeless/Droopy.html.
Taylor, M. and Nygren, A. 2020. Drooping corn ears across Nebraska. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2020/drooping-corn-ears-across-nebraska.
Web sources verified 7/27/22
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ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. 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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