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Drought Effect on Pod Fill in Soybeans

Introduction

 


Figure 1. Aborted soybean seed pods. Shawn P. Conley Soybean and Wheat Extension Specialist Department of Agronomy University of Wisconsin, Madison.

 

Drought Loss Potential in Soybeans

The greatest risk for potential yield loss due to drought stress in soybean occurs during the R4 through R6 growth stages. When drought persists during these growth stages, soybean flowering stops and plants are unable to compensate for lost pods. Research has shown that from the second through the fourth week of seed fill, a 39 to 45 percent yield decrease can occur when there are four days of visible moisture stress. Drought stress during seed fill can also reduce the number of seeds per pod and seed weight. Understanding the differences between how indeterminate and determinate soybean plants react to dry growing conditions may help in the formulation of drought management decisions. (Note, indeterminate soybean plants continue to grow after flowering has begun, while determinate soybean plants essentially halt vegetative growth once flowering begins.)

 

How a Soybean’s Flowering Habit Can Affect Drought Stress Management

Drought stress can affect indeterminate and determinate soybeans differently.

Indeterminate soybean

Indeterminate soybeans continue growing upward at the tip of the stem for several weeks after flowering begins on the lower stem. Flowering will progress up the stem, and plants will continue to flower for six to eight weeks depending on plant maturity and growing conditions. Most northern commercial varieties are indeterminate. Indeterminate soybean varieties usually grow taller and do well in regions with short growing seasons. Indeterminate flowering-type soybean can recover from a short-term drought during the flowering growth stages by producing flowers and pods over a longer period. An indeterminate flowering growth habit should be advantageous to recovery from drought stress.

Determinate soybean

By contrast, determinate soybean plants complete their growth in height and then produce all the flowers at about the same time. These plants are also usually one-half to two-thirds as tall as indeterminate varieties. Most southern soybean varieties are determinate. Drought during this shorter flowering period can negatively affect a higher percentage of the blooms and ultimately yield potential. Severe drought can have a devastating effect on yield potential in determinate soybean varieties, because flowering stops and plants cannot compensate for lost pods.

 

How Heat and Drought Stress Effect the Soybean Plant

Drought Effects

Drought stress can cause flower and pod abortion, while reducing the number of seeds per pod and seed size. Moderate to severe drought stress can also substantially reduce or stop nitrogen fixation, disrupting seed development. If adequate rainfall occurs and photosynthates become available after R5, the plant may compensate for earlier losses by producing larger seeds (within its genetic capacity). Once the plant reaches R6, pods are not normally aborted.

If soybean plants are drought stressed to the point of losing leaves, it is time to decide whether to leave the plants in the field or cut them for hay. This decision depends on the stage of growth and condition of the plant, along with the producer’s need for soybean hay or the market for this type of hay. Plants with 30 percent of the leaves still attached may be considered for hay. These plants can produce 0.75 to 1.25 tons of dry matter per acre with 13 percent protein and 48 percent in-vitro dry matter digestibility.

Heat Effects

It can be difficult to distinguish the effects of high temperature from the effects of water stress on soybean plants. Often these stresses occur together and magnify each other’s effects. Temperatures above 95 °F (35 °C) can severely stress soybean plants, have been shown to substantially decrease pod set, and may potentially increase leaf loss. Very high soil temperatures of 90 °F (32 °C) or above can cause decreased nodulation and nitrogen fixation in soybean. High soil temperatures are most likely to occur on coarse textured soils and in later-planted bean (like those planted into double-crop production systems). While flower production of indeterminate soybeans can occur for 30 to 40 days or more under good conditions, moisture stress and high temperatures can shorten the flowering period.

 

Problems to Consider When Harvesting a Drought-Stricken Soybean Crop

  1.  Smaller seed size. Combines should be adjusted to keep harvest loss of small seeds to a minimum.
  2. Green seeds. Soybean plants that senesce before maturity due to stress may produce green seed that can result in dockage at the elevator.
  3. Green stems. Plants that die prematurely due to drought may have green stems at harvest that can slow harvest by wrapping on the header.
  4. Pod shattering. This is especially problematic if there are weather cycles of wetting and drying before harvest.
  5. Sprouted seed. Drought-weakened pods can allow moisture to infiltrate the pod and reach the seeds. This can result in seeds sprouting while still in the pod.
  6. Poor grain quality. Drought-stricken soybean pods are more susceptible to invasion by fungi, which can result in reduced grain quality.

 

Management Decisions

Managing stress from insect, disease, or nutrient sources can also help reduce the overall stress load on the plant and potentially limit drought stress-associated yield losses. When drought stress becomes severe, a management decision to keep the crop in the field or harvest the soybean for hay should be made when leaves start to curl and plants begin to defoliate. This decision should be based on the crop condition, growth stage, and on hay needs or hay markets.

Any producer who is considering using the production from a drought-stressed soybean crop for planting next year’s crop should understand that seed produced under severe drought stress, especially during the reproductive grow stages, may exhibit reduced germination and vigor.

 

Article Link

 

Sources
Lenssen, A. 2012. Soybean response to drought. Iowa State University Extension and Outreach, ICM News. https://crops.extension.iastate.edu/cropnews/2012/06/soybean-response-drought
Kness, A. 2020. Yield impact on heat and drought-stressed soybeans. University of Maryland Extension, Maryland Extension News. http://blog.umd.edu/agronomynews/2020/08/07/yield-impact-on-heat-and-drought-stressed-soybeans/
Wright, J., Hicks, D., and Naeve, S. 2006. Predicting the last irrigation for corn and soybeans in Central Minnesota. University of Minnesota Extension. Minnesota Crop eNews. https://blog-crop-news.extension.umn. edu/2018/08/predicting-last-irrigation-for-corn-and.html
Desclaux, D., Huynh, T.T., and Roumet, P. 2000. Identification of soybean plant characteristics that indicate the timing of drought stress. Crop Science. 40(3): 716–722. https://doi.org/10.2135/cropsci2000.403716x
Staton, M. 2020. Moisture stress and high temperature effects on soybean yields. Michigan State University Extension. https://www.canr.msu.edu/news/moisture_ stress_and_high_temperature_effects_on_soybean_yields.
Wiebold, B. 2018. Weather woes in the soybean field. University of Missouri. Integrated Pest Management. https://ipm.missouri.edu/croppest/2018/10/weatherWoes/
Dornbos, D.L. Jr., Mullen, R.E. and Shibles, R.M. 1989. Drought stress effects during seed fill on soybean seed germination and vigor. Crop Science. 29(2): 476–480.https://doi.org/10.2135/cropsci1989.0011183X002900020047x
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing,
soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be considered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2024 Bayer Group. All rights reserved. 1322_61731

How Do Cold February Temperatures Affect Insects That Overwinter?

The month of February can be a time of significant temperature extremes through much of the crop growing regions of the United States and Canada. Cold snaps that occur in February, or even during March or April, may cause people to ask if fluctuating temperatures can adversely impact the survival of insect pests, and ultimately affect their populations in the spring and summer months. The short answer is, “probably not.”1 Entomologists and other experts that have studied the impact of extreme cold temperatures on the survival of insects have found that there are a variety of ways subzero temperatures can affect insect populations and that the insect ecosystem is extremely complex, which makes it difficult to predict summer populations based on winter temperatures.

 

How Do Insects Survive Freezing Temperatures?

Insects have evolved coping mechanisms that allow them to survive the fluctuating temperatures that often occur in winter. Most insects overwinter in a certain development stage – egg, larva, nymph, or adult. The two primary strategies for survival are freeze avoidance and freeze tolerance.

One way that freeze avoidance can be achieved is by simply avoiding freezing temperatures. A classic example of this is the migration of the monarch butterfly to Mexico. During the overwintering period, subsequent generations are produced that will make their way in turn to northern regions in the spring.

Insects that do overwinter must seek shelter to buffer them from extreme temperatures or must possess a mechanism that can help them avoid or tolerate freezing through biochemical means. Freeze-avoidant insects can tolerate a certain degree of chilling,
but do not die until the temperature falls below the freezing point for their body fluids – i.e., when ice crystals begin to form in their bodies, rupturing cells and damaging organs. This is because they have the ability to form a type of anti-freeze in their cells prior to winter. The anti-freeze, or cryoprotectant, lowers the freezing point of the body fluid. For many freeze-avoidant species, this lower freezing point is likely between zero and −20 °F (−18 and −29 °C).1,2 Examples of anti-freeze that can be produced by insects include glycerol (the same chemical that is often used to prevent freezing in windshield washer fluids in automobiles) and sugars called trehalose and mannitol. Insects begin acclimating to the cold weather by producing these cryoprotectants in the fall, as the weather turns cooler.

In comparison, freeze-tolerant insects are able to withstand the formation of ice crystals in their bodies by producing proteins that “control” the freezing process. Examples of freeze-tolerant insects include cockroaches, midges, and woolly caterpillars. A second-generation European corn borer can survive in the pupal stage for three continuous months at temperatures as low as −4 °F (−20 °C), even with ice crystals in its body.

 

Cold Weather Protection Using Overwintering Sites

Some overwintering insects find places that protect them from extreme air temperatures and biting wind chills. For example, corn rootworms, Japanese beetles, and wireworms overwinter in the soil, which provides a buffer from extremely cold temperatures and can be further insulated with a blanket of snow. However, dry soil is more susceptible to deeper frost and greater temperature fluctuations than wet soil, and a combination of dry soil and no snow can further reduce the temperature protection available to overwintering insects. Because of this, insects that lay eggs in the soil, such as corn rootworm beetles, typically lay overwintering eggs in the upper 4 inches (10 cm) of moist soil, though they do lay eggs deeper if the upper soil is too dry.

Temperatures below 14 °F (−10 °C) must be sustained for more than one week to increase the mortality rate of western corn rootworm (WCR) eggs. In 2021, soil temperatures were monitored at five locations following a cold snap in Nebraska in which air temperatures dropped to −30 °F (−34 °C). Despite the rapid drop in air temperatures, temperature changed very little four inches
(10 cm) beneath the soil, ranging from a 1 to 8 °F decrease from their initial temperatures of 30 to 35.6 °F (−1 to 2 °C). At all locations, soil temperatures remained well above the 14 °F (−10 °C) threshold necessary to kill WCR eggs.

Alternatively, insects that overwinter above ground—such as bean leaf beetles and European corn borers—shelter in plant debris and crop residue. Bean leaf beetles overwinter as adults and can only survive temperatures above 20 °F (−6.6 °C), so they must seek shelter in wooded areas or under plant litter to avoid extremely cold temperatures. Southwestern corn borers can survive temperatures of 14 to 19 °F (−10 to −7 °C) for several days if they are dry and overwintering in the root crowns of corn. A study done over three winters near Evansville, IN found that even though air temperatures fell below -2.2 °F (−19 °C) for up to five consecutive days, the temperature inside the root crowns averaged 17.6 °F (−8 °C) for periods of a few hours, which the researchers attributed to the temperature-buffering effects of freezing soil water. While the air temperature was low enough to be lethal to the southwestern corn borers, they did not experience those temperatures inside their overwintering sites.

 

How Do Extreme Cold Temperatures Affect Stored Grain Insects?

Stored grain is well insulated. Especially in large quantities, it prevents cold temperatures from reaching the center of the mass. One laboratory study examined the survival of six major stored grain insect species exposed to temperatures of 32 °F (0 °C) for seven days. Five of the six species tested survived that exposure, and only the population of rice weevils was reduced. In another study conducted at Winnipeg, MB, the rusty grain beetle survived two winters in metal structures that contained 1000 bushels of wheat. Outside air temperatures ranged from −4 to −22 °F (−20 to −30 °C) during the two coldest months. Rusty grain beetles will not freeze until temperatures reach −4 °F (−20 °C), so the combination of their freeze tolerance and the insulation from the stored grain allowed them to survive inside the grain mass despite the low temperatures outside the container.

 

Effects of a Mild Winter

Mild winter weather that does not expose insects to potentially lethal temperatures can cause insects to resume activity early in the spring before plants have regrown. Insects that emerge too early can deplete their energy reserves before food sources are readily available, so some insect species rely on cues other than temperature—such as day length—before becoming active again.

 

Effects of Cold Snaps and Fluctuating Temperatures

Sublethal temperatures, while not low enough to cause mortality, can still reduce insect growth, development, and the reproductive potential. The impact of repeated cold cycles is highly dependent on the duration of those cold temperatures.

 

What Happens if Spring Arrives, Followed by a Deep Freeze?

If insect activity has resumed due to a mild winter and/or an early spring, reproduction is likely to follow. Insects use a large amount of stored fat and sugars to survive the winter, potentially leaving them with low reserves in spring that could be further taxed by reproduction. Therefore, if a sudden cold snap occurs in late March or early April, for example, some insect populations could be devastated because they lack the resources to survive the cold.

 

Summary

Insects are very adaptable creatures. The survival mechanisms that they have developed in response to cold winter weather make it unlikely that insect mortality will be high in any given year, except under particularly unusual circumstances.

 

Article Link

 

Sources:
Dean, A. and Hodgson, E. 2020. Survival effects of fluctuating temperatures on insects. Iowa State University Extension and Outreach, ICM News.
https://crops.extension.iastate.edu/cropnews/2020/04/survival-effects-fluctuating-temperatures-insects
2021. The insect freeze-tolerance mechanism. Northern Pest.
https://www.northernpest.com/blog/the-insect-freeze-tolerance-mechanism/
DiFonzo, C. 2023. How insects survive cold: The potential effect of a mild winter. Michigan State University Extension, Field Crops. https://www.canr.msu.edu/news/how_insects_survive_cold_the_potential_effect_of_a_mild_winter
Anderson, M., Dean, A., and Hodgson, E. 2021. Insect overwintering: A bit like Goldilocks? Iowa State University Extension and Outreach, Integrated Crop Management. https://crops.extension.iastate.edu/blog/ashley-dean-erin-hodgson-meaghan-anderson/insect-overwintering-bit-goldilocks
Peterson, J., McMechan, J., Meinke, L., and Bradshaw, J. 2021. How have the cold February temperatures affected insect overwintering in Nebraska? University of Nebraska-Lincoln, CropWatch.
https://cropwatch.unl.edu/2021/how-have-cold-february-temperatures-affected-insect-overwintering-nebraska
Johnson, D. 2015. The inevitable questions about insects surviving the winter. University of Kentucky Extension, Grain Crops Update. https://graincrops.blogspot.com/2015/02/the-inevitable-questions-about-insects.html
Bonjour, E. 2021. Did the extreme cold temperatures kill stored grain insects? Oklahoma State University Extension, EP-20-2. https://extension.okstate.edu/e-pest-alerts/2021/did-the-extreme-cold-temperatures-kill-stored-grain-insects- february-24-2021.html
 Legal statements
Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be consid-ered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions.Bayer and Bayer Cross are registered trademarks of Bayer Group. ©2024 Bayer Group. All rights reserved. 1215_359244.

Managing Stored Grain during Fluctuating Temperatures in the late Fall and Winter

Managing grain quality during late fall and winter is an ongoing chore that can be even more challenging when temperatures fluctuate on a daily basis. To avoid grain quality loss, growers should be aware of what changing temperatures can possibly do to stored grain and what important steps that can be taken to manage grain temperatures.

 

Why changes in temperature can cause storage problems for grain.

Inconsistent air temperatures can occur frequently across much of the grain producing areas of the United States and Canada in late fall and throughout the winter. Checking the condition of stored grain during this period is crucial to maintaining the quality and value of the product. Crusted, wet, or sticky kernels can be signs of trouble inside the grain bin.

Solar radiation in the winter can cause issues when it comes to grain temperature. The amount of solar energy on the south side of a bin in February is much greater than in June. Grain within two feet of the bin walls may be warmer than the average air temperature (Figure 2).

 


Figure 1. Grain bin in winter.

 


Figure 2. Illustrating the effects of potential temperature swings throughout a given day during the fall and winter months.

 

The most important cause of deterioration of dry stored grain is grain temperature. If temperature is not controlled, moisture can migrate from one part of the grain mass to another, where it can accumulate and potentially cause spoilage.

What causes air and moisture to migrate within a grain bin? It is estimated that the air space within a grain mass can range from about 30% to 60% of the total space. The temperature of the air surrounding the grain is about the same temperature as the grain. As average daily temperatures outside of the bin decline in late fall/early winter to 20 °F and colder, the walls of the bin also become cooler. Since grain has fairly good insulation properties, most of the center mass of grain (and the air surrounding the grain) remain at about the same temperature as when the grain was placed in storage. These temperature differences create a circulation of air and moisture known as convection currents. The cooler air surrounding the grain near the bin walls becomes denser and settles near the bin floor. It then migrates toward the center of the grain mass where the warmer grain increases the air temperature, causing it to become less dense and rise through the warm grain. As it rises, the air absorbs small amounts of moisture. Then the air continues to make its way into the upper part of the grain mass and the top of the bin, which is cooler. As it cools, condensation can occur, and moisture is deposited in the grain. This can lead to spoilage (moldy grain) and/or crusting, usually in the top center of the grain surface.

 

What is Equilibrium Moisture Content and why is it important?

Equilibrium moisture content (EMC) is the percent moisture content at which grain will stabilize, given a certain temperature and relative humidity (RH) of the air surrounding the kernels. The EMC charts for several types of grain crops can be found at this link: https://extension.okstate.edu/fact-sheets/aeration-management-knowing-when-to-run-aeration-fans. html.

Why is this information so important to grain storage managers? Regardless of how much air fans supply to a bin, the temperature and RH of that air will dictate whether the grain will decrease or increase in moisture content (MC). The stabilization time is impacted by the amount of air supplied. However, the final grain moisture content is determined by the temperature and relative humidity of the air. If a certain MC is desired for the grain being stored, it is important to know whether air being supplied will either deposit moisture in the grain or remove moisture from the grain. If the desired condition of the grain cannot be met given the temperature and RH of the air, then it is not cost efficient to run the fans. For example (Table 1), if corn is being stored in a bin and the outside air conditions are 50 °F and the RH is 70%, the resulting MC of the grain aerated over time will be an EMC of 15.7% (using the EMC chart for corn found in the link above). If the goal is to maintain or reduce the moisture content, do not run fans in conditions that would cause a higher MC as found in the EMC chart. Once a stored crop is close to a safe storage moisture, aeration can be more efficient. If corn inside the bin is at 16% moisture, and you want to dry it to 15%, running the fan in air condition scenarios A, C, E and F (Table 1) would help achieve that goal, as the EMC’s are lower than 15%. Scenarios B and D would not achieve that goal as the EMC’s are above 15%.

 

Table 1. Equilibrium Moisture Content for corn resulting from three different temperature and two different relative humidity levels.
Air condition scenario Air Temperature (°F) Relative Humidity (RH) Equilibrium Moisture Content
A 40 50 12.7
B 40 70 16.4
C 50 50 12.2
D 50 70 15.7
E 70 50 11.2
F 70 70 14.5
Adapted from Aeration management: Knowing when to run aeration fans. Oklahoma State University.4

 

Tips on managing stored grain during temperature fluctuations.

 

Safety

The dangers of grain handling cannot be stressed heavily enough. NEVER enter a bin when the grain is flowing and be extremely cautious around all grain handling structures and equipment. EXTREME CAUTION should be used if entering a bin with moldy grain or if the upper layer of grain is crusted. Be sure to have safety precautions and emergency plans in place and make them known to all workers and bystanders on the farm.

 

Article Link

Sources:
1Mahrenholz, A. 2022. Keeping your grain safe in fluctuating temperatures. Purdue University Extension.
https://extension.purdue.edu/news/county/pike/2022/03/pike-keeping-your-grain-safe-news.html
2McKenzie, B. and Van Fossen, L. 1995. Managing dry grain in storage. Purdue University Extension. AED-20.
https://www.extension.purdue.edu/extmedia/AED/AED-20.html
3Hellevang, K. 2020. Proper spring grain drying and storage critical. North Dakota State University. Extension and Ag Research News.
https://www.ag.ndsu.edu/news/newsreleases/2020/march-23-2020/proper-spring-grain-drying-and-storage-critical
4Jones, C. 2018. Aeration management: Knowing when to run aeration fans. Oklahoma State University Extension. BAE-1116. https://extension.okstate.edu/fact-sheets/aeration-management-knowing-when-to-run-aeration-fans.html
5Dawson, A. 2013. Knowing when it’s time to turn on the aeration fan. Manitoba Co-operator. https://www.manitobacooperator.ca/crops/knowing-when-its-time-to-turn-on-the-aeration-fan/
Additional sources:
Cloud, H.A. and Morey, R.V. 2018. Managing stored grain with aeration. University of Minnesota Extension. https://extension. umn.edu/corn-harvest/managing-stored-grain-aeration
Legal Statements
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary , from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommen-dations in this material are based upon trial observations and feedback received from a limited number of growers and growing environments. These recommendations should be considered as one reference point and should not be substituted for the professional opinion of agronomists, entomologists or other relevant experts evaluating specific conditions. Bayer and Bayer Cross are registered trademarks of Bayer Group. ©2023 Bayer Group. All rights reserved. 1018_157027.

Field Edge Effect in Corn

Many producers have noticed an “edge effect” when assessing corn yields on the edge of the field as compared to yields on the interior of the field. Yields tend to be lower when the edge is oriented on the south or west side of the field and when adjacent to soybean, hay, or pasture. It is thought that the micro-climate at the field edge causes the edge yield penalty. Interestingly, when corn is grown in a narrow strip intercropped with soybean, the outside corn rows out yield the inner rows presumably because of increased light interception by the outer rows.(1) Research is currently being conducted at Iowa State University to determine the cause for the yield reduction associated with the field edge.(2)

The common explanation for this phenomenon is that hot and dry winds, blowing from the south or west across a lower statured crop (soybean, hay, pasture) to a corn field impact the outer corn rows by increasing the heat and/or drought stress. As temperature increases, the vapor pressure deficit increases as the surrounding air is much drier than the interior of the leaf. This in turn creates an increase in water demand by the corn plant, and in some cases it can double.

But that can occur throughout the field, so why does it impact just the field border?

The plants on the field border, particularly on the border that receives the prevailing hot and dry winds can have an increased vapor pressure deficit as the air at the leaf surface is continually replaced by drier air. In turn, this increases water demand by the plant and if this occurs in conjunction with a soil deficit, then the plant suffers stress resulting in a yield reduction.(3)


Figure 1. Note the stressed corn on the border with the road on the left and foreground.

 


Figure 2. Stressed corn along the field border with road.

Article Link

Sources
1 Winsor, S. 2011. Farming on the edge: Strip intercropping edges capture more light, reward with higher yields. Farm Progress. https://www.farmprogress.com/precision-ag/farming-edge-strip-intercropping-edges-capture-more-light-reward-higher-yields/.
2 White, T. and Licht, M. 2020. Corn edge effect on-farm project. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/blog/mark-licht-tyler-white/corn-edge-effect-farm-project/.
3 Westgate, M. and Vittetoe, R. 2017. Addressing the edge or border effect on corn yields. Integrated Crop Manage-ment. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/blog/mark-westgate-re-becca-vittetoe/addressing-edge-or-border-effect-corn-yields/.
Web sites verified 9/29/22.
Legal Statements
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.
Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2022 Bayer Group. All rights reserved. 1214_79442

Corn Leaf Diseases

KEY POINTS

• Different diseases may have similar symptoms, particularly during the early stages of disease development.
• It is not uncommon for a corn plant to have several different diseases present at the same time.
• Multiple diseases present on a corn plant can make disease diagnosis difficult.

Anthracnose Leaf Blight

Symptoms of anthracnose leaf blight include small, oval to elongated, water-soaked lesions that appear on youngest leaves and turn tan to brown with yellow to reddish brown borders (Figure 1). Small, black, hair-like structures (called setae) may sometimes be seen in the middle of lesions. Lesions may coalesce, blighting the entire leaf. Heavily infected leaves wither and die. Leaf symptoms are most common on the lower leaves early in the season and on the upper leaves late in the season. Infection occurs in warm, humid weather. The same fungal pathogen is responsible for both anthracnose leaf blight and stalk rot; however, the presence of leaf blight does not necessarily indicate that stalk rot will be a problem later in the season. The stalk rot phase is of greater concern than the leaf blight phase.


Figure 1. Anthracnose leaf blight with setae in lesions

 

Common Rust

Common rust causes small, cinnamon-brown, powdery, circular-to-elongated pustules to occur on upper and lower leaf surfaces, often in bands across leaves (Figure 2). In contrast, pustules of southern corn rust are orange-colored and occur primarily on the upper leaf surface. Rust pustules rupture the leaf surface (epidermis) and powdery rust spores can be rubbed off. Pustules become dark brown to black late in the growing season. The disease is favored by moderate to cool temperatures and high humidity. The fungus does not overwinter in the Corn Belt.


Figure 2. Common Rust.

 

Southern Rust

Similar to common rust, southern rust symptoms are small, circular, light cinnamon-brown to orange-colored pustules occur on upper surfaces, leaf sheaths, and husk leaves (Figure 3). Pustules often are very dense in areas of infected tissues. Pustules break the leaf surface (epidermis) less frequently than common rust. Infection is favored by warm, humid weather.


Figure 3. Southern rust.


Eyespot

Eyespot appears as small, circular to oval, translucent lesions surrounded by yellow to purple margins that gives them a halo effect (Figure 4). Lesions occur on leaves (most commonly as plants approach maturity), sheaths, and husks. The disease is favored by cool, moist weather


Figure 4. Eyespot


Gray Leaf Spot

Gray leaf spot has gray to tan, rectangular lesions on leaf, sheath, or husk tissue (Figure 5). Spots are opaque and long
(up to 2 inches). Lower leaves are affected first, usually not until after silking. Lesions may have a gray, downy appearance on the underside of leaves where the fungus sporulates. The organism thrives in extended periods of warm, overcast days and high humidity. Gray leaf spot has become more prevalent with increased use of reduced tillage and continuous corn.


Figure 5. Rectangular shaped
lesions of gray leaf spot.


Physoderma Brown Spot and Node Breakage

Physoderma brown spot first has small yellow spots that appear at the base of the leaf and over time turn brown in color. As infection progresses, spots can often be found occurring in bands across the leaf. Spots in the mid-rib of the leaf become reddish to brown in color and combine to form irregular blotches (Figure 6). Sheath, husk, tassel, stalk, and leaves may exhibit symptoms late in the season. Infected stalks may break at a node. This disease is favored by warm, wet weather.


Figure 6. Physoderma brown spot.


Northern Corn Leaf Blight

Long (up to 6 inches), elliptical to cigar-shaped, gray-green lesions that become tan, brown are symptomatic of infection by northern corn leaf blight (Figure 7). Infection begins on lower leaves and moves up the plant. Lesions may form in bands across leaves because of infection in the whorl. The disease is favored by high humidity and moderate temperatures.


Figure 7. Cigar shaped lesions
of northern corn leaf blight.


Southern Corn Leaf Blight

Southern corn leaf blight produces small, elongated (up to 1-inch long) parallel-sided lesions that are tan with brownish borders (Figure 8). Symptoms vary considerably on different corn products, often requiring microscopic examination of the fungal structures to confirm diagnoses. This blight primarily attacks leaves and is favored by high humidity and warm temperatures.


Figure 8. Southern corn leaf  blight.


Goss’s Wilt

This bacterial disease causes both a seedling and adult-plant wilt. Adult plant wilt is typically associated with leaf blight, not Goss’s Wilt. Systemically infected seedlings may wilt and die. Vascular bundles can be discolored. More common later-season infections of leaves produce dull gray green to necrotic lesions often with irregular margins. Small, water-soaked “freckles” appear within developing lesions (Figure 9). Bacterial droplets may ooze from infected tissues early in the morning, leaving a shellac-like appearance when dried on leaf surfaces. Plant injury, such as hail or wind damage, enhances infection.


Figure 9. Goss’s wilt leaf freckles and ooze.


Stewart’s Bacterial Wilt

Symptoms of Stewart’s wilt or Stewart’s disease on leaves are long, green-gray, water-soaked lesions with wavy margins, accompanied by stunting and wilting which may lead to plant death at the seedling stage (Figure 10). Cavities may form in the stalk near the soil line. The more common leaf blight phase appears after tasseling. Leaves are streaked with gray green to yellow-green lesions, each distinguished by the presence of a flea beetle feeding scar toward the base of the streak. Streaks are long and irregular, turning tan as the tissue dies. Flea beetles are the primary vector, and incidence of the disease is relative to the size of the beetle population.


Figure 10. Stewart’s wilt water-soaked lesions with wavy margins.


Tar Spot

A relatively new disease, tar spot was first found in
the Midwest in the mid 2010’s. It is a fungal disease and is primarily found on the leaves. The symptoms include small irregularly shaped black lesions on both upper and lower leaf surface that cannot be rubbed off (Figure 11). It can also produce lesions that have a halo appearance with the black spots surrounded by a tan to yellowish halo circled with a dark border, referred to as “fish-eye” lesions. A field diagnostic technique is to wet the leaf and rub the lesions between your thumb and index fingers — tar spot lesions will not rub like rust spores on the leaf surface, for example. Corn products that are susceptible can be infected at any developmental stage when conditions are favorable. The pathogen overwinters on infested corn residue and serves as a source of inoculum for the following season. Management includes burying residue, crop rotation, tolerant corn products, and fungicides. An application, Tarspotter, is available to assess the risk of tar spot.For more information see: https://www.dekalbasgrowdeltapine.com/en-us/agronomy/tar-spot.html


Figure 11. Tar spot.


Management

Timely scouting is important to help protect corn plants from diseases caused by fungal pathogens.
Since much of a corn plant’s energy from photosynthesis is produced by the leaves immediately surrounding the primary ear, those leaves should be protected from foliar diseases, if possible. Fungicide applications made before a fungal disease spread throughout the corn canopy may help maximize yield potential in high disease pressure environments. However, since Goss’s Wilt and Stewart’s wilt are both caused by bacterial pathogens, these diseases are not affected by fungicide applications. Fields with foliar diseases should be scouted for stalk health as the reduction in photosynthesis can predispose corn plants to stalk lodging. Identification of foliar diseases can help determine the need for future management practices such as tillage, crop rotation and the selection of disease-tolerant corn products to help reduce disease occurrence next season.

Article Link

Sources:
1. Bissonnette, S.M., Pataky, N.R., Nafziger, E.D., et al. 2010. Field crop scouting manual. X880e.
University of Illinois Extension.
2. Brouder, S.M., Camberato, J.J., Casteel, S.N, et al. 2014. Corn and soybean field guide, 2014 edition.
ID-179. Purdue University.
3. White, D.G. 1999. Compendium of Corn Diseases, third edition. The American Phytopathological Society.
4. Hershman, D.E., Vincelli, P., and Kaiser, C.A. 2011. Foliar fungicide use in corn and soybean.
University of Kentucky. PPFS-GEN-12. http://plantpathology.ca.uky.edu/.
5. Kleczewski, N. et al. 2019. Tar spot. Crop Protection Network.
https://crop-protection-network.s3.amazonaws.com/publications/tar-spot-filename-2019-03-25-120313.pdf
Legal Statements
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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Causes & Effects of Shorter Statured Corn Within the Stand

 


Figure 1. Corn in V5 growth stage.

 

Drivers of Internodal Growth

Stalk elongation begins at the V5 growth stage (Figure 1). Most cell expansion occurs at the base of internodes and is affected by light and shade interactions, day length, and temperatures. Later planting dates often result in taller corn because longer days typically produce elongated internodes. Corn fields with high populations can have a ‘shading effect’. This shading leads to increased auxin production.1 Auxin is a plant growth hormone that helps facilitate the expansion of internodes, resulting in taller plants. Conversely, intense solar radiation can reduce auxin levels, leading to less internode elongation (Figure 2).


Figure 2. Shortened internode on plant to left compared to normal internode elongation on right.

Cell wall expansion within the internodes is limited by cold temperatures, and internodes may become rigid if exposed to a cool period during vegetative growth. Therefore, early planting dates can be associated with short corn heights as they have a higher chance of being exposed to cool spring weather and shorter day lengths. Earlier planting dates usually result in shorter corn compared to later planting dates as early planted corn has more vegetative growth occurring when days are shorter, soils and air temperatures are cooler, and often in saturated soils. Saturated soil is unfavorable for root and shoot development and is prone to compaction when driven on during spring field work. Compacted soil from equipment can lead to shorter corn in rows adjacent to the tracks.2 Early root development that is inhibited from these early-season conditions can limit moisture and nutrient uptake during the rapid growth stage of corn. Water stress can impact plants with normal root development as cell expansion depends on water uptake. Reduced water uptake can result in shorter internodes because of limited water availability.

Impact on Pollination and Yield Potential

Most corn plants reach full height by the end of pollination. Corn heights may appear to even out across the field as tassels completely emerge. Successful pollination of shorter corn within the stand is still expected; however, full canopies are needed to reach yield potential. While shorter plants within the stand may yield less than neighboring full-size plants, pollination is expected to be successful.

An early planted field with short plants interspersed with tall plants can have a higher yield potential than a later planted field with uniform tall plants. Even when plants appear to be short or non-uniform, growing conditions result in the field having similar or greater yield potential compared to later planted fields. Additionally, the yield penalty for replanting a field may be greater than potential yield loss from an uneven stand.(4)

Article Link

Sources
1Nielsen, R. L. 2001. Short corn at tasseling. Purdue University. https://www.agry.purdue.edu/ext/corn/news/articles.01/short_corn-0712.html
2Larson, E. 2016. Will short corn limit your yield potential? Mississippi State University. https://www.mississippi-crops.com/2016/06/09/will-short-corn-limit-your-yield-potential/
3Nafziger, E. 2022. Assessing potential of the 2022 corn crop University of Illinois. https://farmdoc.illinois.edu/field-crop-production/assessing-potential-of-the-2022-corn-crop.html
4Licht, M. 2023. Uneven corn heights. Iowa State University.
https://crops.extension.iastate.edu/encyclopedia/uneven-corn-heights
Legal Statements
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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Effects of Flooding on Corn Emergence and Young Corn Plants

Key Points

Survival of Corn Plants

There are differences among corn products in response to flooding. Generally, germinating seeds will survive for four days. Longer flooding results in lower yields especially at lower nitrogen levels. The effects of flooding on yield potential depend on the growth stage of corn, length of time corn is submerged, and temperature. Corn plants need oxygen to survive, and oxygen is depleted after about 48 hours.1,2 Corn plants at or below the soil surface are at the highest risk of dying when the field is flooded. Submerged seedlings that are at or below the soil surface can survive for 2 to 4 days.2 Emerged corn and corn with a growing point above water have a better chance of survival. Temperature is one of the most critical components of plant survival while the field is flooded. If temperatures are above 77° F, the plant may not survive 24 hours beneath water.1 If temperatures are cooler (<77° F), corn with fewer than six leaves can survive approximately four days of flooding.(1)


Figure 1. Corn younger than the six leaf growth stage can survive four days of flooding.
Daren Mueller, Iowa State University, Bugwood.org.

 

Potential Flooding

Problems Significant loss of nitrogen (N) through denitrification or leaching can occur in corn fields submerged for more than two days. Saturated soils result in denitrification, which tends to be more prevalent in heavier-textured soils, whereas leaching is more prevalent in sandy soils. Soil moisture can increase N losses due to denitrification. Research conducted in Nebraska indicated approximately a 10 to 25% nitrate loss when soil is saturated for 5 and 10 days, respectively.3 This was reported while soil temperatures were between 55 and 60° F. Sidedressing more N is a possible solution if considerable N was lost in the field. As wet soils dry, the soil surface can form a crust potentially inhibiting seedling emergence. Fields may be at greater risk for soil crusting if they have:

A rotary hoe can help break up the crust and aid seedling emergence. Timing is essential, and breaking the crust as soon as possible is most beneficial. Without disease infection, cooler soils can allow seedlings to survive longer as they break through the crust.

Scouting and Replanting Options

It is important to scout corn fields 3 to 5 days after the water has receded.1,2 Pull up seedlings and look at the growing point. A white or cream-colored growing point that is still firm means the plant is recovering. Growing points that are darkening and soft are beginning to die.2 Stand counts need to be taken to determine plant population.

Several options are available if a field needs to be replanted. Guidance can be obtained from the corn (growing degree days) GDD Tool at located at High Plains Regional Climate Center (HPRCC), https://hprcc.unl.edu/agroclimate/gdd.php. It will provide GDD for any location in the Midwest for any starting date and end date. In addition, forecasts are provided using historical data for physiological maturity in relation to corn product relative maturity that can help determine the best relative maturity choice for replanting.

If replanting with corn, minimum or no tillage is recommended to maintain the efficacy of any herbicides and/or soil insecticides already applied to the field. Switching to alternative crops when replanting corn fields must be carefully considered. Before replanting with soybeans, check your herbicide label and consult local experts to determine if the previously applied corn herbicides could damage the replanted crop. It is important to scout fields entirely before making the decision to replant.


Figure 2. Flooded fields.

Article Link

Sources
1Elmore, R., Daugherty, R.B., and Mueller, N. 2015. Corn and soybean survival in saturated and flooded soils. University of Nebraska-Lincoln. Cropwatch.unl. edu
2Thomison, P. 2005. Ponding effects on corn. Corn Newsletter. Ohio State University Extension.
3Ferguson, R.B. 2008. Assessing nitrogen loss due to saturated soils. University of Nebraska-Lincoln.
4Al-Kaisi, M. and Pedersen, P. 2007. Wet conditions: challenges and opportunities. Iowa State University Extension. Integrated Crop Management.
Other information:
Elmore, R. 2014. Flooding and Corn Survival. University of Nebraska-Lincoln. https://cropwatch.unl. edu/flooding-and-corn-survival Elmore, R. and Specht, J. 2014. Early-Season Flooding and Soybean Survival. University of Nebraska-Lincoln. https://cropwatch.unl.edu/early-season-flooding-and-soybean-survival
Legal Statement
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. Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved.1222_124643

Considerations on Cold and Corn Planting

 

Asking the What Ifs:

There will always be risk involved, no matter when a grower decides to plant. The few Ifs will always come to mind.

But many factors affect the amount and timing of environmental stress. Determining the greatest risks are judgement calls that vary from one grower to the next.

Factors to Consider:

These above-mentioned factors could impact each operation differently. However, certain facts relating to corn planting and management must be taken into consideration when deciding to plant into less-than-ideal conditions.

Corn Germination and Quality

 


Figure 1. Seedling development impacted by cold imbibition.

 

Management Options

 

Takeaway Points

We cannot predict the future to assure a perfect crop stand, but we can analyze conditions and assess risks to help in determining the best corn planting options.

Article Link

Sources
1Knox, S. 2018. Cold germination test for corn and soybeans. Crop Watch. Institute of Agricultural and Natural Resources. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2018/cold-germination-test-corn-and-soybeans
2Elmore, R., Specht, J., Ress, J., Yang, H., and Grassini, P. 2018. Cold soil temperature and corn planting windows. Crop Watch. Institute of Agricultural and Natural Resources. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2018/cold-soil-temperature-and-corn-planting-windows
3Thomison, P., Paul, P., and Hammond, R. 2015. Corn planting nearing completion—time to troubleshoot emergence problems. The Ohio State University Extension. C.O.R.N. Newsletter. https://agcrops.osu.edu/newsletter/corn-newsletter/2015-14/corn-planting-nearing-completion
4Nafziger, E. 2015. Planting into cool soils—yes or no? University of Illinois. The Bulletin. https://farmdoc. illinois.edu/field-crop-production/crop_production/planting-into-cool-soils-yes-or-no.html
5Nielsen, R. L. 2012. Early planted corn and cold weather. Corny News Network Articles. Purdue University. https://www.agry.purdue.edu/ext/corn/news/articles.12/EarlyCornColdWthr-0412.html
Legal Statements
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.
Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1222_64397

Rootless Corn Syndrome

Causes & Symptoms

“Rootless corn syndrome”, sometimes called “floppy corn syndrome”, occurs in young corn plants when the root system is limited or there is a lack of permanent root system development (nodal roots). During permanent root system establishment, young plants (V2 to V4 growth stages) are vulnerable to environmental stress factors, particularly hot and dry surface soils, but also shallow planting depths, compacted soils, and loose or cloddy soil conditions. If young plants lack enough root support, the occurrence of strong winds or thunderstorms can cause plants to lean and fall over (lodge). Affected plants lack all or most nodal roots; any existing nodal roots may appear stubby, blunt, and not anchored to the soil (Figure 1).

Factors that Prevent Good Permanent Root Development

Under normal soil conditions, nodal roots begin developing at the growing point (crown) located where the top of the mesocotyl and base of the coleoptile meet. If corn seed is planted 1½ to 2 inches deep, then the nodal (or crown) roots begin developing at about ¾ inches below the soil surface. However, in rootless corn scenarios, the nodal roots may have stopped developing because upper soil conditions were too dry. Young roots that emerge from the crown area of the plant will die if their root tips dry out prior to successful root establishment in moist soil.

How Corn Plants are Impacted

In addition to anchoring the plant, the nodal roots are vital in providing water and nutrients that the corn plant needs for normal growth and development. Therefore, due to a lack of root mass, rootless plants may wilt or eventually die in extreme conditions. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume. After lodging, adequate rainfall can promote crown root development and many plants may recover. However, recovery is severely hampered if conditions are dry.

What May Help

Row cultivation may help plants with rootless corn syndrome by placing soil around the base of the plant to help with support. Cultivation may also aid in new root development if rain occurs. Cultivation can also help with soil aeration and improve growing conditions for young plants. In the end, however, adequate rainfall to promote new nodal development and deeper reaching roots to anchor the plant is the best solution.

Article Link

Sources
Licht, M. and Vittetoe, R. 2021. “Floppy Corn – another side of effect of dry conditions. Iowa State University. Extension and Outreach. Integrated Crop Management. https://crops.extension.iastate.edu/blog/mark-licht-rebecca-vittetoe/%E2%80%9Cfloppy%E2%80%9D-corn-%E2%80%93-another-side-effect-dry-conditions#:~:text=The%20dry%20conditions%20are%20causing,a%20look%20at%20the%20roots.
Nielsen, R. 2022. “Rootless” or “floppy” corn syndrome. Corney News Network. Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/floppycorn.html
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.
Bayer and Bayer Cross are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. ©2023 Bayer Group. All rights reserved. 1214_59231