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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
Latham Hi‑Tech Seeds

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
Latham Hi‑Tech Seeds

Protect Soybeans from Cold Temperatures
Many of our minds are already on the upcoming planting season. This week someone posed the following question, “How hard of a frost can soybeans withstand?”

It’s a great question, so I wanted to address the topic of early planting a bit, well, “earlier” than usual!

The first thing to keep in mind is that cold temperatures at or before planting can negatively affect the growing point of the plant. For corn, that growing point stays under the soil surface until the V5-V6 stage, helping protect the plant to a certain degree from colder weather spells for several weeks. For soybeans, however, the growing point comes out of the ground at emergence. Therefore, a soybean seedling is immediately vulnerable to cold weather.

Using a fungicide seed treatment will help protect young soybeans from seedling diseases at this early stage, but they are not designed to protect against cold temperatures. Soybeans typically require over 100 growing degree units (GDU’s) to accumulate before emergence, which is similar to corn that requires about 125 GDU’s. Abiding by the minimum soil temperature of 50 degrees Fahrenheit will keep you away from poor emergence and the seedling disease risk associated with soil temps below 50 degrees. That’s why I suggest watching the weather forecasts before you plant soybean seed, and do your best to ensure hard frosts (which take place at 28 degrees Fahrenheit) are no longer possible.

Remember, when soybeans emerge, they have a growing point at the base of each cotyledon and at the main shoot. The main shoot is the small leaves in-between the cotyledons. If you notice brown on the stem below the cotyledons, the plant will not recover. Early planting is proven to provide higher yields, but it is is fine balance between the two, so watch weather forecasts and soil temperatures so you can find the balance on your own farm.

Additional tips to keep in mind before planting:
1. Grab a clump of soil and watch how easily it crumbles. If it stays in a ball, conditions are NOT right for planting. If it crumbles easily, the soil is fit for planting.
2. Make sure your planting date is covered in your farm insurance policy – this includes your “do not plant before” dates. If you plant outside those dates, your insurance could be jeopardized.
Team Latham

April 1, 2019

Agronomics, Crop, Emergence, Frost, Season, Soybeans, Tech Tuesday, Weather, Winter
Latham Hi‑Tech Seeds

Identifying and Controlling Cutworms

Cutworms are insects that show up during the earliest growing stages of the season. The presence of cutworms can pose a threat to the well-being of corn plants, but their severity is highly variable and depends on the species. Delayed planting and corn plants shorter than 18 inches are most susceptible to undergoing severe damage from cutworms.

Black Cutworm

Black Cutworm

Black cutworms are the most common species found in corn throughout the Midwest. The larvae of black cutworms can be up to 1¾ inches long with their appearance characterized by a dark-gray segmented body. Black cutworms are most likely to be seen between stages VE – when the shoot first emerges from the soil and V5 – when the first five leaves exhibit visible collars. The sets of paired spots unequal in size that run along the length of the black cutworm make it distinct in appearance. Black cutworms cause damage by chewing holes in leaves and larvae will cut the lower portions of the corn plant just above the soil line. The youngest larvae will feed on leaves whereas older cutworms will feed exclusively below ground level. The first generation of black cutworm will cause the most damage, though three to four generations can be produced in a year.

The black cutworm thrives best in wet and weedy fields with poor drainage. Cover cropping can make conditions conducive for the growth of laid eggs, especially if weeds are prevalent. Insecticide is advised if cutting is evident across 2-3% of corn plants and larvae do not exceed ¾ inch in length.

Dingy Cutworm

Dingy Cutworm

Similar to the black cutworm, dingy cutworms can form larvae up to 1¾ inches long and often emerge in fields with heavy crop residue. However, unlike black cutworms, the pairs of black dots running along the segmented back appear to be equal in size. When fully grown, dingy cutworms reach a size of one inch in length. Dingy cutworms typically only feed on leaves and do not cut plants.

Glassy, Bronzed and Sandhill Cutworms

Glassy Cutworm

These three classes of cutworms are characterized predominately by the color of their larvae. Glassy cutworms have a white, translucent segmented body with a solid orange head and cause damage primarily to seedlings.

Bronzed cutworms are colored with light orange, bronze and brown stripes running the length of their body.

Like glassy cutworms, sandhill cutworms have a translucent, light brown body that is uniform in color, including the head. Glassy cutworms are known to cause cutting damage in addition to chewing and feeding damage exhibited by other cutworms.

Sandhill Cutworm

Bronzed Cutworm

What to Look for When Scouting

Corn plants succeeding soybeans or legumes are most susceptible to hosting cutworms. With shorter corn plants having the greatest vulnerability to cutworm damage, scouting should begin once seedlings first emerge and continue until plants achieve a height of 18 inches tall. Look for signs of cutting, wilting and irregular holes on leaves. Uneven stand or inconsistencies in cutting across rows are also signs of cutworm damage.

Cutworms gravitate toward moist soil for burrowing. When looking for signs of infestation, dig around the base of plants to look for burrows ranging in size from three to four inches. When soil is dry, dig deeper to three inches below ground to identify burrows.

Treatment

As cutworms are associated with reduced stand resulting from cutting or wilting, yield can subsequently be decreased. However, replanting is not usually necessary and is only advised if the presence of cutworms is not under control and stand has been severely impacted.

Controlling weeds can reduce overwintering and can remove an environment favorable for hosting cutworms. Tilling practices that reduce weeds and field residue will deter moths looking to lay eggs in the fall. Reduced tillage or no-till, delayed planting and overwintering cover crops are all management practices that increase chances of cutworm damage. If you see cutworm damage on 2-3% of plants and they are smaller than ¾ inch, it’s time to spray. When pre-applying insecticides to dry or crusted soils, it is advised to work the treatment into the soil so it is able to reach cutworms and burrows housed below ground.

Photo Credits

Black Cutworm: Iowa State University Extension and Outreach

Dingy Cutworm: Purdue University

Glassy Cutworm: University of Minnesota Extension 

Sandhill Cutworm: Iowa State University Department of Entomology

Bronzed Cutworm: Iowa State University Department of Entomology

Latham Seeds Precision Agronomy Advisors

April 1, 2019

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

Spring 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.

Spring Frost in Soybeans

If frost damage occurs below the soybeans’ cotyledons – the first leaves that emerge above ground – the plant will mostly likely fail to recover. Wilted and dried leaves will often remain on the plant after a frost event. In recovering soybeans, new leaves will emerge at the site of cotyledons – the first pair of embryonic leaves that appear above ground. If auxiliary buds growing at the juncture of the plant’s stem and cotyledons are not frozen, the plant is on track for recovery.

Spring Frost in Corn

Since corn plants are protected by soil for a longer period of time relative to soybeans, they are less susceptible to lethal frost injury. However, temperatures below 28°F can cause damage below the soil and compromise growth, leading to poor stands. Once the growing point is above ground, corn plants exposed to 32°F for a few hours and 28°F for a few minutes can be lethal. After an initial frost, continued cool temperatures can decrease yield due to the onset of stalk rot diseases.

If frost occurs before V6, yield loss is minimal. In recovering corn plants, you should see new leaf growth emerging from whorls. Yellow-colored tissue that exists above the growing point is a sign of regeneration.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Frost, Soybeans, Weather
Latham Hi‑Tech Seeds

Flooding and Saturated Soils

iStock Photo

For corn and soybean plants before and after emergence, flooding and saturated soils can jeopardize yield. Germinating seeds require oxygen to survive. After the first 48 hours following a heavy rain or flooding event, oxygen levels in the soil will become entirely depleted and prevent seeds from germinating and continuing to grow.

Yield loss for corn and soybeans depends on the duration of the flooding event and at what growth stage it occurs. The longer a plant is submerged or growing in saturated soil, the less likely it is to survive. Generally, smaller seedlings with lower stamina are less likely to survive following a heavy rainfall event compared to larger seedlings.

Warmer temperatures are associated with higher growth rates, and as a result, a higher amount of oxygen is used. When temperatures exceed the mid-70° range, survival may not exceed 24 hours following the heavy rainfall event.

Effects on Corn Plants

Before V6, the growing point is below ground and damage from flooding is more likely to impact yield or kill the plant.  After V6, corn plants fair better in saturated conditions if some of the plant is out of the water. However, the higher temperatures can speed up respiration and oxygen requirements, leading to more plant damage compared to cooler temperatures during a flood event.

Nitrogen loss is another way flooding impacts corn yields. Corn consumes two-thirds of its nitrogen by the start of the reproductive stage and relies on a functional root system. If a flooding event compromises plant roots, yield can be reduced significantly. Research from Iowa State University found that a 30-inch corn plant that had been flooded for 48 hours with minimal nitrogen uptake experienced a 20% reduction in yield. Flooding can also promote seed decay, crazy top that exhibits proliferated tassels, stunted ears or completely barren plants

Impacts on Soybeans

For soybean plants at stages V2 or V3, survival is possible. However, nitrogen fixation can be restricted and reduced yield is still likely. For soybeans submerged for less than 48 hours, yield loss is rarely observed.

Once the first bloom appears at stage R1 the number of pods per node will be greatly decreased if sitting in saturated conditions. Wilting, stunting and yellow-leaves will be expressed in damaged or dying soybean plants. Further, research has found that greater yield reduction has been observed in soybean plants grown in heavy clay soils as opposed to silt loam soils.

Assessing Outcomes

Flooding and prolonged saturated soils pose the greatest threat to young plants that have yet to emerge above ground. As water recedes, any remaining residual mud on corn and soybean plants can reduce photosynthesis. For plants that survive a flooding event, they will be more vulnerable to diseases and stresses over the course of the growing season.

The survival outlook for saturated seeds and germinating plants will not exceed four days. Plants that survive after water levels recede will continue to grow within three to five days.

Latham Seeds Precision Agronomy Advisors

April 1, 2019

Agronomics, Corn, Crop, Flooding, Soil, Soybeans, Weather
Latham Hi‑Tech Seeds

States Focus on Nutrient Reduction Strategies
Reducing the excessive use of nutrients was the focus of presentations made recently during the annual Agribusiness Showcase and Conference in Des Moines.

Most Upper Midwest farmers are very aware of problems in the “Hypoxia Zone” of the Gulf of Mexico. This area where the Mississippi River discharges into the Gulf is negatively affected by the abundance of nitrate nitrogen (N) and phosphorus (P) found in the river water. Excess nutrients can come from many sources including: sewage treatment plants; soil erosion; deposition of atmospheric nitrogen and fertilizers used on farms; lawns; and golf courses.

The EPA in March 2011 issued a letter to encourage states bordering the Mississippi and Missouri Rivers to reduce contaminants, specifically N and P, found in lakes, rivers, streams and groundwater. Phosphorus is tightly bonded to soil particles, so erosion is the main reason it is found in water. Nitrogen, on the other hand, converts to nitrates and easily leaches down through the soil profile. This allows nitrates to infiltrate groundwater and eventually reach lakes, streams and rivers through tile systems or aquifers.
Below are a few recommendations from experts who spoke at the agribusiness conference:
- Eliminate “insurance” and “build” applications of nutrients. We tend to base our fertilizer needs on soil tests and what our yield goals are, then add an extra 10-20% to make up for losses due to weather, timing, etc. We need to stop this practice.
- Bioreactors at the field’s edge can lower nitrate in runoff water before it can enter a stream or tile drainage ditch.
- Saturated Buffers can help reduce both erosion and nitrate runoff for farms that have a river or stream flowing alongside or through the field.
- Cover Crops can greatly reduce erosion and help with more efficient nitrogen use. Cover crops are one of the few practices that may help an entire field, rather than merely an edge-of-field strategy. Long-term benefits of cover crops include managing weeds, increasing organic matter and building overall soil health.
- Precision Agriculture. Programs like Climate FieldView™ and Latham’s Data Forward™ bring economics and conservation together by using your own farm data. This leads to better variety selection and crop input decisions and often better use of soil and fertilizer resources.
- These are just a few of the most popular strategies, but you could visit with your local NRCS staff member for more ideas. Most state strategies are voluntary, but Minnesota is considering making some of their strategies mandatory. Fall application of nitrogen fertilizer might be the first practice banned in Minnesota.
- One farmer put it very simply, “Either join the effort now and have some freedom in what practices you use or wait until it is mandatory and then be told what to do.”
Contact your Latham RSM or our Technical Agronomist Phil Long to talk about ways our cover crop portfolio or Seed-2-Soil® services can help you and our customers raise the most profitable and sustainable crops.
Mark Grundmeier, Product Manager

March 19, 2019

Agriculture, Cover Crops, Crop, Industry News, Tech Tuesday
Latham Hi‑Tech Seeds

5-Year Cover Crop Plan

Looking to implement cover crops on your farm? Phil Long walks through a 5-year plan to get started. Tune in below!

Laura Cunningham

March 7, 2019

#AskTheAgronomist, Agronomics, Cover Crops, Crop, Soil