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Anthracnose Stalk Rot
Credit: Crop Protection Network

There are a variety of stalk rots that infect corn, causing extensive damage to crops and losses in yield. Common factors make corn susceptible to stalk rot including warm and wet weather, stress after pollination, fertility issues, stalk boring insects, and the presence of other foliar diseases. There are key signs, symptoms and differences that distinguish the different types of stalk rot.

Anthracnose stalk rot is the most common type of stalk rot and is caused by the fungus Colletotrichum graminicola. The fungus is favored by wet, warm weather and overwinters in corn residue. Signs of the disease will be observed four to six weeks following pollination.

Scouting for Signs and Symptoms

The disease undergoes three phases with distinct signs and symptoms:
- In the first phase, foliar lesions will appear in the early part of the growing season. The leaf blight will begin on the lowest leaves, and will reach the upper leaves by late season.
- During the second phase, top-dieback will appear in the middle part of the season after tasseling, killing the parts of the plant located above the ear.
- In the third phase, shiny black lesions will appear on outside surface of stalks. Look for setae, or bristles that cover the surface of the stalk. A hand lens can be used to look for the bristle-like texture and black dots in the center of lesions.
Stalks will exhibit fragility and appear to be brittle when handled. Different from other forms of stalk rot, anthracnose stalk rot will cause plants to lodge at the upper portion of the stalk. Pinching or bending at the nodes can be used to test for stalk lodging.

Stalk rot can lead to death just before maturity and reduce yield. In addition, plants defoliated from hail damage and those that are nitrogen deficient are at an increased risk for being infected from the stalk rot.

Management Strategies

Planting hybrids with resistance to stalk rots is a helpful defense against these diseases.
Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Disease, Fall, Season, Summer
Latham Hi‑Tech Seeds

Rust Diseases in Corn

Southern Rust. Credit: Crop Protection Network

Common Rust and Southern Rust infect corn in the late summer. The diseases generate raised spores known as “pustules” on the surface of leaves, leading to reduced yield and poor grain quality.

Common rust (Puccinia sorghi) and southern rust (Puccinia polysora) fungi are unable to overwinter in the Midwest and require a host plant to remain alive. The spores created by rust diseases are transported by wind to the Midwest from Southern states.

Temperatures ranging from 61–77° fuel the growth of rust diseases. Cool and humid temperatures, especially when exhibited overnight, can further drive the development of the fungi.

As long as the weather conditions are right for rust diseases, the cycle of spore development will continue. The return of hot and dry weather can prevent further development of the fungus and kill off the spores.

Implications

Rust can reduce yield and decrease grain quality. Foliar damage from rust diseases can interfere with water transpirationand reduce photosynthetic leaf area.

Nutrients designated to support plant growth are rerouted in response to the damage incurred by leaves. Damage from rust diseases deplete carbohydrate reserves in corn leaves. As a result, the plant will begin sourcing the nutrients from stalks and roots, leading to reduced yield and stalk rot.

Common Rust. Credit: Crop Protection Network

Scouting for Rust Diseases

While common rust has less of an impact on yield, southern rust has been found to reduce yield by 25 bu/acre in corn with no fungicide application. The fungi can begin to infect plants under favorable conditions in as little as six hours.

Southern rust signs are evident on the upper leaf surface and are round, as opposed to elongated in plants infected with common rust. The pustules will be orange compared to the darker color of common rust. Overtime, southern rust pustules will become brown or black.

Common rust pustules are found on the upper and lower leaf surface and are oblong. Common rust pustules will be brick red in appearance and can coalesce to kill parts of leaves. In order to determine the difference between common and southern rust pustules, use a magnifying lens to inspect the leaf surface.

Management

Planting early is one of the best ways to reduce corn’s vulnerability to rust diseases. Corn planted late in the season is most susceptible to experiencing yield loss and grain damage. Many hybrids are also equipped with resistance to rust diseases, though the extent to which they are protected from the fungus can vary.

When pustules are observed on 50% of scouted plants, it is advised to begin implementing a treatment plan. Fungicides can also be used to treat corn infected with common and southern rust. Be sure to consult with your local Latham representative to determine the best management options for rust diseases.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Disease, Fall, Season, Summer
Latham Hi‑Tech Seeds

Western Bean Cutworm

Credit: Iowa State University

The Western Bean Cutworm can dramatically reduce end-of-season corn profit. The Western Bean Cutworm does not cut stalks but feeds on ears, posing as a threat to grain quality and corn yield. The cutworm moths are gray to brown with a wing span of 1 ½ inches. As a late summer insect, moths first emerge in early July and only one generation is produced each year.

Female moths lay eggs in whorls just ahead of the pollination stage and will lay an average of 50 eggs at a time. Eggs develop over the course of 5 to 7 days. Eggs will first be white, then become tan as they develop and will turn purple once they are close to hatching.

Only a small percentage of eggs typically survive, but larvae that reach full maturity can cause measurable damage to corn.

Scouting and Implications

Pheromone traps can be used to identify Western Bean Cutworm in fields. When multiple moths are caught at a high frequency, scouting for symptoms should take place. When scouting, focus on fields that are close to shedding pollen and examine 20 consecutive plants in 5 different locations.

Credit: Purdue University

Western Bean Cutworms feed on leaf tissue and silks as they approach the ear where most of the damage is incurred. The Western Bean Cutworm can be confused with other species of cutworm. The dark brown stripes behind their head that appear during the third instar distinguishes them from other cutworms.

The most mature larvae will feed on fully developed ears and can sometimes burrow into the sides of the ear. When scouting, it is important to pull back the husks to fully determine if the cutworms are present.

After feeding on the ears, the larvae will drop to the soil and burrow deep underground where they overwinter. It is common for many larvae to feed on one ear at once, increasing the severity of feeding damage. Ears with multiple larvae can exhibit up to 50-60% in kernel loss.

An average of one larva per plant has resulted in yield loss of 4 bu/acre in Iowa and Nebraska. Aside from yield loss, damaged kernels are prone to mold growth which reduces overall grain quality.

Managing Western Bean Cutworm

Managing Western Bean Cutworm should take place close to hatching, just before pollination. Once larvae hatch and move underneath tight leaves surrounding the ear, they become difficult to exterminate. Applying a foliar insecticide is recommended when 5-8% of plants have egg masses or young larvae present but not before at least 90% of plants have emerged tassels.

SmartStax, Viptera, and eventually we will have Duracade traited hybrids that provide aboveground protection against Western Bean Cutworm. Though Western Bean Cutworm overwinters, there is no evidence that tillage is an effective way to combat infestation. Be sure to consult with your local Latham representative to design the most effective treatment plan.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Insects, Season, Summer
Latham Hi‑Tech Seeds

Fall Frost Damage in Corn and Soybeans

Frost damage occurs in corn and soybeans when plants are exposed to freezing or below-freezing temperatures. Damage can occur to the plants above and below the soil when temperatures range from 28 to 32°F and colder. Corn and soybean plants exposed to air temperatures below 28°F are often lethal and prevent plants from undergoing full recovery from injuries. The key in assessing frost damage is waiting five days to allow for any potential growth recovery or rehabilitation to occur.

Credit: Michigan State University

Fall Frost in Soybeans

Once soybeans begin maturity and already have developed pods, they are most often immune from frost injury. Soybeans placed in narrow rows can have more protection from freezing air temperatures in being covered by leaf canopies. Pods growing on the lower portion of the plant are less vulnerable to frost damage than those on the top part of the canopy. Injured soybeans exhibit elongated pods that shrink to smaller than normal sizes upon drying. Most yield loss occurs during the full seed maturity stage.

Soybeans damaged by frost should be dried at a temperature no higher than 130°F and may have lower oil content. Both frost damaged corn and soybeans may also have delayed dry down.

Credit: University of Minnesota

Fall Frost in Corn

Frost-damaged corn can exhibit softened kernels prone to breakage and should be dried at temperatures below 160°F and be stored at a moisture level no higher than 14%. The storage life for frost-damaged corn will be cut in half and damaged corn should be handled separately from uninjured corn.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Fall, Frost, Season, Soybeans, Weather
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Nitrogen Deficiency in Corn

Photo credit: University of Minnesota Extension

Nitrogen is an essential nutrient and its depletion can lead to severe yield loss. Nitrogen deficiency can be difficult to spot as different hybrids exhibit different symptoms. Most corn plants deficient in nitrogen will exhibit pale-yellowish leaves with a spindled appearance.

Nitrogen is a mobile nutrient and moves to the newest leaves first, leaving the oldest leaves more susceptible to deficiency. By moving from the oldest to youngest leaves, signs of yellowing will often form a “V” pattern on the plant leaf.

Causes of Nitrogen Deficiency

Cold or saturated soils are the primary causes of nitrogen deficiency in corn. Periods of heavy rainfall increase nitrogen leaching, depleting saturated soils of the vital nutrient. Aside from soil leaching, nitrogen can be lost through denitrification – where the nutrient is converted to a gas form and lost in the atmosphere.

When soil conditions are dry, sandy or poorly fertilized, early-applied nitrogen fails to be absorbed by plants. Insect diseases that injure root systems can further prevent proper absorption of nitrogen and lead to deficiency.

Other unavoidable circumstances happen later in the growing season when the increase in plant height and density can block sunlight absorption and reduce photosynthesis. This leads corn to use nutrient reserves within the plant, which will weaken stalks.

Implications

60% of the nitrogen needed to support corn growth is built-up between V4 and pollination, making this an important time to monitor for deficiency. Scouting for nitrogen deficiency should also take place after episodes of heavy rainfall.

While having negative implications on yield potential and crop quality, nitrogen deficiency can also contribute to other corn disorders including tip-dieback and kernel abortion. Plants that are nitrogen deficient will cannibalize their stalks to compensate for the nutrient loss. This makes stalks more vulnerable to lodging and pinching.

Management Options

Tissue sampling can provide insight into how severe deficiency is. When testing for nitrogen deficiency in corn, gather samples from different areas of the field to compare nitrogen levels in deficient corn with healthy plants.

Nitrogen deficient corn should be harvested early in order to prevent additional yield loss from stalk lodging. When planning for next year’s crop, avoid planting hybrids with a history of poor nitrogen uptake. Some hybrids also demand a higher level of nitrogen during grain fill than others, so it is important to consider when planning for the next crop.

Be sure to consult with your local Latham representative to determine the best plan for managing nitrogen deficiency in corn.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Fertility, Growth Stages
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Anthracnose Leaf Blight

Photo Credit: University of Minnesota

Colletotrichum graminicola is a fungal pathogen that causes anthracnose leaf blight. Anthracnose leaf blight is a foliar disease that appears in the early and late stages of growth in corn plants. The fungus survives in infected corn residue that remains in the field over the winter. The disease creates elongated lesions with a dried, brown appearance across the length of the leaf blade and is bordered by a darker reddish-brown color.

In the earliest part of the season, leaf blight will impact the lower leaves of the plant and expand toward the top of the plant by late season. The upper part of the plant will begin to exhibit early senescence while the lowest part of the corn plant will remain green and healthy.  This is a characteristic of the Top Dieback part of this disease.

Disease Causes

Anthracnose leaf blight develops predominately from the infected residue left behind in the field. No-till, reduced till and corn on corn rotations can increase the likelihood of the disease to emerge. Though no-till and reduced-till methods are critical for preventing erosion and other corn disorders, it can lead to the accumulation of corn debris that is conducive for housing the fungal pathogen.

The fungus thrives in a warm and wet environment. Moisture from rainfall will often create black specks that appear across the lesions. Wind can also act as a transportation method for the fungus as spores can travel by air or water.

Implications and Treatment

The disease will infect at the seedling stage, causing foliar damage, and end at the growing season, causing stalk rot. Although anthracnose leaf blight has the potential to occur later in the growing season, early signs of the infection do not guarantee that it will resurface closer to harvest. Iowa State University researchers state that because of the early-season nature of the leaf blight, impacts on yield are rarely demonstrated. The late season stalk rot phase of the disease tends to be more detrimental on yield and harvestability.

Crop rotation and the use of resistant hybrids are the best ways to combat leaf blight. Fungicides can keep anthracnose leaf blight in control, but it likely will not be effective for combatting the stalk rot phase. Further, corn hybrids that provide resistance against the earliest stages of leaf blight are not often effective for preventing the onset of late-season stalk rot.

If tillage is used, methods that bury infected corn residue can prevent leaf blight from emerging again during the next season. Crop rotation has also been deemed as an effective way to prevent the continued onset of anthracnose leaf blight. For corn that has perpetually been impacted by leaf blight, two-year rotations away from corn are also advised.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Disease
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Imbibitional Chilling

Causes of Imbibitional Chilling

Imbibitional chilling occurs during the process by which crops absorb water prior to germinating, a phase known as imbibition. Under optimal conditions, seeds should be planted when soil temperatures are above 55°F. When seeds are planted in soils below optimal temperature, the uptake of cold water can damage cells and cause seeds to rupture. This can lead seeds to become shriveled and cause seedlings to emerge late, in a corkscrew shape, or not at all.

If an injured seed eventually develops into an emerged seedling, it can become more vulnerable to disease or damage from herbicides. The risk of imbibitional chilling especially increases when soil temperatures fall below 50°F. Imbibitional chilling or cold injury can occur within 24 to 36 hours of planting, making the relationship between planting timing and soil temperature critical.

Preventing Chilling Injury

As the injury to seedlings occurs after planting, there is little preventive action that can be taken aside from planting when soil temperature is optimal. In the best case, if enough time is afforded between planting and the drop in soil temperature, a seed is less likely to undergo chilling if it is able to absorb warm water. There are ways to determine if imbibitional chilling has occurred after planting. When scouting, look for signs of inconsistent emergence. If a plant looks to be missing, dig into the soil around the area to see if a seedling can be found. If it has a corkscrew shape, underwent leaf emergence below ground, or is missing parts, these are also signs of imbibitional chilling. Delayed emergence of a seed can be the result of reduced seed vigor that can result from imbibitional chilling.

Soil temperatures should be monitored and averaged for the week preceding the projected planting date. To determine the soil temperature on the chosen planting day, take the temperature of the soil just after sunrise – the coldest part of the subsequent 24-hour period. Soil temperature changes more slowly than air temperature, but air temperature can still be a strong indicator for what to expect with soil temperature. If it is projected that soil temperature will remain above 50°F for 24 to 48 hours after planting, imbibitional chilling can be avoided.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Emergence, Soybeans, Spring
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Rootless Corn Syndrome

Credit: Iowa State University

Rootless corn syndrome is a disorder, often a result of hot and dry soil surfaces and planting into dry soil. With rootless corn syndrome, the nodal roots will fail to attach to the soil. Nodal roots are essential conduits for transporting water and nutrients to corn plants. Their absence is highly consequential for the quality of stand and overall yield outcomes.

Dry soils warm more rapidly than moist soils, and combined with conventional tilling, corn plants can become susceptible to failed nodal root development. Heavy rainfall and planting when the soil is too wet can compact the soil, preventing nodal roots from extending downward.

The erosive effects of rainfall and wind combined with shallow planting depth are the primary drivers of rootless corn syndrome. In addition to weather-related causes, when corn is planted at a depth less than 1 inch below the surface, nodal root development can take place at a depth shallower than what is needed for having access to moist soil. Nodal roots should form between 1 to 1.5 inches below the surface.

What to Look for

Nodal roots first appear around the V1 and V2 stage. Rootless corn occurs in plants with poorly developed root systems and is usually observed in plants from about V3 to V8. When rootless corn syndrome is suspected, look for signs of lodged and collapsed corn plants. Corn plants may still be standing but later on they will lose vigor and fall over. Test plants in the area of concern by tugging on them to determine whether nodal roots are established and growing down.

Preventative Action

Rootless corn can largely be prevented by ensuring that seeds are planted at least 1.5 to 2 inches below the soil surface. For corn plants whose nodal roots fail to grow, the prospects for survival are bleak. Corn nutrient and water uptake hinges on having a developed nodal root system. For plants that do survive, poor stands and low vigor will be exhibited.

Moving soil to cover roots may allow them to recover – but if an operation is following a no-till plan, this may not be viable. Further, row cultivation for bringing soil around nodal roots will be ineffective if the soil below the surface lacks moisture for supporting recovery. Adequate rainfall and the absence of drought conditions will support optimal nodal root development and prevent rootless corn syndrome.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Disease, Drought, Emergence
Latham Hi‑Tech Seeds

Corn Rootworm

Left to Right: Southern, Western and Northern Rootworm. (Credit: Iowa State University).

Corn rootworm causes negative impacts for farmers every year. On average, corn rootworm costs farmers $1 billion annually, with costs equating to $800 million in lost yield and $200 million in treatment expenses.

The Western, Northern and Southern corn rootworms are three variations of this insect. They grow to be ¼ of an inch long when fully mature. The larvae appear white in color with a dark brown head. After mating in the late summer months, rootworm eggs overwinter and eventually hatch in May or June of the following year.

Rootworm Causes

Rootworms develop across four stages – egg, larvae, pupa and adult. The larvae feed on roots which leads to lodging and overall poor plant stand. Adult rootworms feed primarily on corn silks which can interfere with pollination, leading to lost yield.

Rootworm Larvae (Credit: Iowa State University)

The greatest impacts on yield and quality of stand are larvae feeding on the nodal roots. Mature rootworms tunnel throughout the root system and cause significant damage or death to corn plants. Root feeding and tunneling alone can lead to a loss in yield of up to 50 percent.

While rootworms primarily feed on corn, weeds are also a food source for larvae and mature beetles. Moist soil conditions with high organic matter content create favorable conditions for females to lay their eggs.

Scouting and Treatment Options

When scouting in the spring and early summer, dig up corn plants and check for damage on the root system.  Look for signs of tunneling or larvae actively feeding on roots. Placing the roots of a corn plant along with attached soil in water and waiting for larvae to float to the surface is another strategy to use. In the later stages of summer, watch for beetles feeding on corn ears and silks.

North Dakota State University found that complete loss or severe damage to a single root node can lead to a yield loss of 15 to 18 percent. Crop rotation is considered the best method for combatting continued infestation.

Below is a chart to help guide your insecticide application decision.

We have Latham® hybrids equipped with resistance to rootworm have been deemed an effective method for staving off infestation. Contact your local Latham® representative to determine which hybrids will work best for combatting corn rootworm.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Insects
Latham Hi‑Tech Seeds

Armyworm

The true armyworm – not to be confused with the fall armyworm – can pose a threat to corn stands and overall yield as an early season pest. Armyworm larvae are characterized by alternating light and dark bands.

The larvae feed primarily on seedling leaves and are associated with causing defoliation. When feeding, armyworms start at the base of the corn plant and work their way up, primarily feeding on softer leaves and during the nighttime. During the day, armyworms will migrate to the whorl of the corn plant as well as inside of soil cracks.

Cool and wet weather in the springtime supports the development of armyworms and fields with a heavy presence of weeds and grasses are conducive for allowing them to thrive. Armyworm moths migrate up from the south and look for the grassy fields or areas with lush vegetation. Therefore, winter rye cover crops have been associated with a higher prevalence of armyworm infestation. That is why it is important to terminate cover crops at least two weeks prior to corn planting.

Treatment and Mitigation

Death in corn plants from armyworm is not common, but if the armyworm feeds on a budding corn plant, this can lead to poor stands and significant loss in yield. When armyworm infestation causes defoliation in more than 25% of corn plants, it is advised to begin using an insecticide. Additionally, when armyworms are still developing and larvae is only ¼ to ¾ inches in length, treatment is considered economical and is advised.

Controlling excess grass growth will prevent moths from laying eggs and will offer protection from future infestation. If herbicides are applied, the loss of a weed habitat can drive armyworms to feed predominately on corn plants.

Treating an armyworm infestation with small corn plants requires quick decision making because large populations of armyworms can spread quickly across a field. Keep an eye on those fields that have a cover crop or are close to armyworm habitat. Be prepared to act if conditions warrant treatment!

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Insects