It’s time to scout soybeans!! Tune in for a 10 minute soybean blitz on what to look for in the field.
| Insects: Japanese Beetles | 1:55 |
| Insects: Gall Midge | 2:35 |
| Insects: Aphids | 3:55 |
| Diseases: Sudden Death Syndrome | 4:45 |
| Diseases: Frog Eye | 6:10 |
| Diseases: Soybean Cyst Nematode | 7:14 |
| Disorders: Iron Deficiency Chlorosis | 8:22 |
| Disorders: Root Development | 9:33 |
| Disorders: Herbicide Injury | 10:55 |
If you’re fortunate to be done with planting your crops, it’s time to get back out there and check your stands. This year I’m especially concerned with soybean stands for three main reasons:
Walking fields right after emergence gives you the most time to make corrections or to replant. Stand reductions rarely occur evenly across a field. That’s why I recommend taking 10 stand counts in the area where the problem is the worst, as well as taking 10 counts in an area that was not affected or is slightly affected. Most university researchers recommend keeping a final stand of at least 100,000 plants per acre.
University trials also indicate that planting soybeans on or before June 1 in northern Iowa and southern Minnesota gives 95% of expected yield. It is usually June 15 before soybean yields drop below 85% of what is expected. Over the years, we have seen decent soybean yields when soybeans were planted around the 4th of July.
Scouting early and often is the best advice I can give, so you can remedy the situation as soon as possible. Different insects, diseases and pests may be present due to weather conditions and stage of crop development. Scout diligently all growing season long!
Rotting of soybean stem and root tissue, or “damping off,” can jeopardize stand quality and reduce yield. The Phytophthora fungi can impact seedlings both before and after emergence. Even if seedlings successfully emerge above the soil, they will have poor vigor and slow early growth.
Poor stand is one of the primary consequences of damping off, though replanting may be possible. North Dakota State University research cites that Phytophthora-related yield loss has reached up to 30% in states throughout the Midwest.
Cool weather is a major cause of damping off as it slows germination and stifles growth. Phytophthora thrives in soil temperatures between 70 and 77°F but can also survive in extremely cold temperatures. Warm temperatures, poor drainage and/or clay soils create a susceptible environment for damping off.
Before seedlings emerge, the fungi can cause seeds to rot. Rotten seeds will appear to be caked in soil with discolored roots. Roots may not be fully developed or even exist.
Wilting can occur in emerged seedlings as the cotyledons will appear brown and saturated. Plants that developed leaves before showing signs of damping off will begin to turn a grayish color before turning brown.
Damping off can sometimes be confused with herbicide injury. Whereas fields impacted by herbicide injury will have uniform damage, damping off will create inconsistent patches of impacted crops.
With the overwintering nature of the Phytophthora fungi, controlling the amount of field residue can make the environment less conducive for fungal growth. Also, when planting early or in fields with poor drainage consider using fungicide seed treatments to protect seedlings.
Varieties equipped with genes resistant to Phytophthora will protect plants after they emerge and later in the season as well. Contact your local Latham® representative to determine which varieties will work best for your needs.
Sclerotinia stem rot – also known as White Mold –can lead to significant yield loss in soybeans. Yield loss from white mold is attributed to the damage it causes to leaves, pods and stems. Research from the University of Wisconsin estimates the disease has costed growers in the U.S. and Canada 101 million bushels of soybeans – equal to $1.2 billion.
White mold is caused by the fungus Sclerotinia sclerotiorum and overwinters in the soil for a number of years. After the fungus emerges from the soil, mushroom shaped structures known as apothecia will form on the soil surface. The apothecia, ranging between ¼ and ½ an inch wide, will first infect through soybean flowers before it reaches the stem.
While the fungus primarily spreads through the air via spores, moisture is required for infection to take place. As a result, cool and wet weather along with high humidity are the main causes of white mold.
While Sclerotinia sclerotiorum is often confused with other fungal pathogens, the sclerotia distinguishes white mold from other look-alike diseases. Symptoms of white mold will be most prevalent between R3 and R6. Infected plants will exhibit white fuzzy growth on the lower stem.
Soybean blossoms are the first area of the plant to exhibit signs of infection and neighboring stems and pods may appear water-saturated. After infecting blossoms and pods, white mold may eventually spread through the entire stem causing it to turn tan or bleached of color. As the mold growth becomes thicker, black spots will begin to surface throughout the fuzzy white surface.
White mold also creates foliar symptoms, causing leaves to completely die while still attached to the stem. In infected soybeans, the tissue area between the leaf veins will turn gray and cause leaves to become wilted and curled.
Due to the overwintering nature of the sclerotia, a two to three-year rotation away from soybeans is advised. When it comes to genetics, some soybean varieties are more resistant to white mold than others. Varieties with resistance to the fungus may recover better than others. It is also important to consider planting practices that cause white mold growth. Shade created from high plant density and growing canopies can lead to the fungal disease. Increasing row width and reducing planting populations are the best methods to improve airflow through the canopy and reduce infection from white mold.
In addition, broadleaf weeds are notorious for hosting white mold and herbicides should be used to control weeds. Fungicides are a viable method for treating white mold and can reduce the negative impacts incurred by soybeans. However, they are most effective when applied just before infection takes place. Be sure to consult with your local Latham representative to determine the best treatment plan for white mold.
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.
Physoderma stalk rot is caused by the pathogen Physoderma maydis, the same fungus responsible for causing Physoderma brown spot. The fungal disease seems to be showing up in more and more corn fields each year, but typically shows up on random plants and and has minimal impact on yield. Like most stalk rot diseases, warm and wet weather favor the development of Physoderma stalk rot.
Physoderma stalk rot infects corn between the V4 and V9 stages. The disease is not associated with any foliar signs, so it is important to inspect plants closely at the base. Dark brown or black lesions will appear at the base of the stalk, and rotting of the pith will be observed upon splitting the stalk open. Overtime, blackening of the pith will move to higher nodes. Sporangia can also be found on the outside of nodes and within the rotted pith tissue.
Scout for symptoms of Physoderma stalk rot across five areas of the field. Stalks will make a distint “pop” and snap at one of the first 3 nodes above the soil line. If more than 10 to 15% of plants exhibit stalk rot, the field should be harvested early.
With this being a newer disease we are still learning differences in hybrid tolerances to both stalk and foliar phases of this disease.
As a majority of stalk rots overwinter, one to two-year rotation away from corn and controlling corn residue are key for preventing the return of the disease. Fungicides may also be applied to prevent Physoderma leaf blight , but these studies are in early phases as well given the novel nature of this diesease
Frogeye leaf spot is a foliar disease caused by the fungus Cerospora sojina. The fungus primarily spreads from infected plants through air and water droplets. During particularly wet years, frogeye leaf spot can lead to yield loss as high as 30%.
Warm, humid weather and heavy rainfall are key drivers of frogeye leaf spot. Areas with standing water and high moisture are notorious for hosting the fungus and fuel the damaging disease. Soybeans grown year after year in the same field are also more susceptible to frogeye.
Frogeye leaf spot most often infects plants after flowering, and signs are most evident in the upper canopy of plants. Dark spots with a gray center and a red-purple border will form on infected eaves. The smaller spots can join to create larger lesions, leading to defoliation that can reduce photosynthetic leaf area.
In addition to causing defoliation, frogeye leaf spot often leads to premature leaf drop. The disease can also infect stems and pods. Later in the growing season, reddish-brown lesions will form on stems and turn the centers of the stems gray. Gray or brown cracked seeds can also form as a result of the disease and pods will be discolored with long lesions.
Selecting varieties with resistance to frogeye leaf spot is the best way to prevent the disease. As the fungus Cerospora sojina is able to overwinter, tillage practices that reduce weeds and bury residue will decrease the likelihood of future infection.
Fungicide application for treating frogeye leaf spot is most effective between the R2 and R5 growth stages. Be sure to consult with your local Latham representative to determine the best strategy for managing frogeye leaf spot.
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.
The disease undergoes three phases with distinct signs and symptoms:
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.
Planting hybrids with resistance to stalk rots is a helpful defense against these diseases.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.