What is the army cutworm?
The army cutworm larvae is an early season pest of several crops including alfalfa. They reach 1.5 to 2 inches in length. They are pale greenish-gray to almost brown in color with no real distinctive markings. They tend to be more of a problem in our western service region but outbreaks east of there are not uncommon. They begin to feed on alfalfa plants soon after plants break dormancy, preventing spring green up.
What is the life cycle?
Only one generation is produced each year. Moths emerge from the soil in late June and fly to mountainous areas and enter a period of inactivity through July and August. In the fall, moths fly back to the plains to lay eggs. Eggs hatch and larvae feed on alfalfa plants until late fall and then overwinter in the soil. Fall soil moisture is required for larvae to survive. When spring arrives and the soil warms, larvae emerge and begin to feed. Once larvae are mature, they pupate 2-3 inches below the soil and emerge as adult moths in June once again.
What damage can army cutworms do?
They feed on stems and leaves of alfalfa plants, preventing spring green-up. Although cutting of plants in established stands is unlikely, new seedings may be prone to cutting by the cutworm. Large numbers of cutworms can be very damaging and consume largeamounts of vegetation. Outbreaks can appear suddenly in the spring and are favored by dry summers followed by a wet fall.
What is the economic threshold?
For established alfalfa stands, 4 to 5 larvae per square foot usually warrants treatment, while new seedings may require treatment at 2 larvae per square foot. Fields should be monitored as soon as conditions allow for alfalfa to break dormancy in the spring. Larvae will likely be just beneath the soil surface during the day as they prefer to feed at night or on overcast days.
How is this pest controlled?
Army cutworm larvae have many natural enemies, including birds, predatory beetles, and wasps which can reduce populations. Although helpful, these beneficial insects cannot be relied upon as a control measure. If the economic threshold is reached and the initial spring growth is being affected, insecticide treatment will provide the best results. The pyrethroids Warrior and Mustang Max are both very effective. Best control will be obtained if applied when the larvae are still small (1” or less).
What is Brittle Snap)?
This is the condition where rapidly growing stalks are broken by strong, sudden winds, associated storms and similar related weather activity. During rapid growth, the cell walls are extremely fragile and stalk tissue may be at a greater risk of brittleness compared to other growth stages.
What Factors Affect Brittle Snap?
Many factors affect brittle snap severity. The timing and velocity of the wind are the most obvious, coupled with the hybrid involved. Heavy winds during cool morning hours will cause more brittle snap than if the wind occurred during the heat of the day when plants are more flexible. Strong-rooted hybrids with less give at the base will have more brittle snap than a shallow-rooted variety. Conditions that favor rapid growth will increase the incidence of brittle snap; some of these conditions include adequate nitrogen, high temperatures, good soil moisture and the use of growth stimulator herbicides such as 2,4-D, dicamba, and clopyralid. Field geography, soil type and crop management practices also influence brittle snap severity.
When is a Corn Plant Most Susceptible to Brittle Snap?
During a corn plants vegetative growth phase, rapidly elongating internodes are often brittle and susceptible to breakage. The two most common periods for brittle snap are the V5 to V8 stage, or when the growing point is just emerging from the soil line, and the V12 to R1 stage, which is about the two weeks prior to tasselling, until just after silking.
The V5 to V8 Stage?
When the growing point is just emerging above the soil line, the corn plant is entering a period of rapid change. The nodal root system is beginning to expand rapidly so the plants ability to take up water and nutrients is increased dramatically which enhances faster leaf and stalk growth in the plant. Fast growth means the cell walls become thinner or are more fragile. Also at this stage of growth, the many nodes and internodes are arranged together in a small area. This concentration may make the plant less flexible and more susceptible to breakage. Brittle snap at this stage usually occurs below the growing point so snapped plants usually do not recover.
V12 to Tasselling?
At this time the corn plant is going through its most rapid stage of growth. This is the 21 to 28 day time period when the corn plant increases in size from about 3 feet to its mature.
It appears corn ears have tipped back more than normal in a large number of fields and seed brands across a wide geography in the corn belt this year. What can we blame this on? Well, the list is long for possible causes of ear tip back from year to year. Drought, excessive post pollination heat, shortage of nutrients, hail, insects, disease, high planting populations, and genetics are just some of the many things that get blamed for this. Sometimes it’s a combination of more than one and sometimes it’s hard to pinpoint anything at all for why it happens. I would agree that in some instances loss of nitrogen can be to blame in those fields that were water logged early and often this year. But what about those fields showing excessive tip back that we know are not short of fertilizer, did not get flooded or hailed, have no real disease or insect pressure, experienced no drought, and are not planted at high populations? What about these that look absolutely beautiful and healthy but when you walk in and pull back ears, you see 3 inches of tip back? The answer isn’t always clear cut and may be fairly complex. One thing is certain. A stress or stresses at the time period following pollination triggered the corn plant to abort some of the kernels at the tip of the ear. Although there has been very little drought stress to our corn crop this year we have to remember drought stress and heat stress are not the same. A corn plant would rather go through its ear fill period at moderate temps than at temps much above 86 degrees. We did have a prolonged period of excessive temperatures during the post pollination period this year. Those nights where temps failed to dip below 70 degrees can be especially detrimental to grain fill and starch accumulation. This may have played a direct roll in some of this excessive ear tip back we are seeing in some fields this year. I would not try blaming it on any one hybrid either. Yes you will see some hybrids do it much worse than others at locations but I think it’s more about the way that specific hybrid responded to it’s environment at that location than the hybrid itself. The above picture shows two ears that I pulled from fields last week over 100 miles apart. The hybrids are both tipped back significantly and they share absolutely no genetic relation. In summary, the corn plant is a complex plant physiologically and reacts to the many different curve balls mother nature throws its way. As always, keep an open mind when trying to determine why things happen in a corn field. Often times there is no one absolute right or wrong answer.
When temperature and moisture conditions favor normal plant development, tassels emerge and begin to shed pollen one to three days before silking. Pollen shedding generally occurs early to mid-morning, after the dew has dried off the tassel. Since pollen is light, it may be carried by the wind one-half to one mile, but most will fall within 50 feet of the tassel. Pollen shed occurs for about one week; peak production is usually on the third day. It is estimated that one tassel can produce between 2 and 5 million pollen grains. Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry, and begins again when temperature and moisture conditions are favorable. On a typical midsummer day, the peak pollen shed occurs between 9 and 11 a.m. Under favorable conditions, released pollen will remain alive for 24 hours. For pollination to occur, silks must be receptive during the time that pollen is shed. The first silks to emerge are those from the base of the ear progressing to the tip. Pollination occurs when a pollen grain lands on a receptive silk. After pollination, the future kernel will start to develop in approximately 30 hours. Adequate moisture is extremely critical for successful pollination. When moisture is short, silks may grow very little, if at all, during the day. Most often, poor pollination results when the silks were not receptive the same time as pollen was available (often described as a poor nick in fields). Very high plant populations will delay silking more than pollen shed, especially under moisture stress. Silks also dry rapidly under hot, dry conditions and may not have enough moisture to support pollen germination and subsequent fertilization of the ovule. Failure of ears to set kernels during pollination can be attributed to:
- pollen killed by high temperatures
- blasted tassels preventing pollen shedding
- silks not receptive to pollen and
- tassels shedding pollen before silks emerge.
In most cases during hot weather, poor pollination is a result of tassels shedding pollen before silk emerges.
Most cropping seasons see delayed emergence problems show up in corn and soybeans somewhere in the Cornbelt. I would like to help answer the question of what conditions cause emerging corn to be delayed. Agronomists commonly point to three major conditions for delayed emergence in corn: inadequate moisture, inadequate temperature, & poor seed-to-soil contact. Herbicide overdose, insect feeding, and diseases can also play a role in delayed emergence, but are considered secondary conditions.
Corn seed takes a certain amount of consistent moisture to emerge. Moisture levels can change within a small area or affect an entire field depending on the soil characteristics and the microclimatic conditions of the field, resulting in delayed emergence. In addition, a hard rain can create a crust barrier on the soil surface that will prohibit emergence to varying degrees depending on the characteristics of the crust matrix such as thickness.
Even though corn seed can begin emerging when soils are 50° F or higher, corn likes to emerge when the temperature is consistently above 55° F. where the seed is placed (seed zone). Some of the things that can reduce temperature and lead to delayed emergence are poor soil characteristics, dense surface residue, above normal moisture, and deep placement of the seed.
Corn seed does not sprout well when it is surrounded by air, water, or plant residue. Only soil structure that completely surrounds a seed provides the right environment for germination. Mostly to a lesser extent, herbicide injury, insect pressure and disease pressure can cause delayed seedling emergence. These categories should be suspect after the 3 main categories have been ruled out.
What are the effects on yield?
A corn seedling is considered late emerging if it is more than a week behind a neighboring plant. If the delay becomes severe enough, the late plant will not be competitive. This situation produces a barren plant, which is essentially a weed to the other corn plants. As a general rule, if more than 2 stages of vegetative growth exist between adjacent plants, the younger of the two will be barren. University studies estimate a yield loss of 5 to 20 percent can occur if the emergence of the late seedlings is 10 days or more.
- Scout the fields during emergence 2-3 locations & 30 feet of each planter unit
- Choose the correct depth for your field conditions that year. Current & Future soil temperature & moisture conditions.
- Check the actual planter depth in the field. Does calibration match in-field results?
- Plant at a consistent depth. This may mean slowing down to speeds less than 5.5 mph when planting.
Most universities base Nitrogen (N) fertility recommendations on a target yield. The assumption is that the target yield is accurate and that the crop is removing what was supplied. Excess N can leave corn vulnerable to rapid growth, poor stalk quality and increased lodging, and delayed maturity. Whatever formula you use to determine N needs, your N levels after removing the crop should be low and levels from year to year should not be increasing.
Ammonium works best in the fall for 2 main reasons. First, it is usually the cheapest source of N available, and second, if applied when soils are cool (soil temp at 2-4" depth is <50°F), the N stays in ammonium from instead of converting to nitrate which is susceptible to leaching. If in doubt about keeping the ammonium from nitrifying, use N-Serve* to stabilize the ammonium in the soil over the winter. Some areas have no choice about using a nitrogen stabilizer like NServe because of lighter soils. Furthermore, some areas are too sandy to do any fall fertilizing and must have broadcast in-season N applied to be at the lowest leaching risk.
--Advantages to Fall Application
Fall application redirects resources from spring to fall to when you have time available. Fall application is good insurance against getting fertilizer in late due to bad weather in the spring. In some years, it also protect against rising fertilizer prices. Soil sampling is usually much easier in the spring when the weather pattern is warm and dry.
--Disadvantages to Fall Application
The time period from when fertilizer is put down to when the next crop needs it leaves the fertilizer vulnerable to the environment. Nitrification of ammonium to nitrate is possible, which then leaves the N in a vulnerable from which can be leached away from where the crop can use it.
Gray Leaf Spot is an economically important disease in many midwestern and eastern corn belt states. It was initially detected in the southeastern coastal corn growing states of Virginia, Georgia and the Carolinas in the 1920s. In those states it was limited to the corn grown in foggy, humid, mountainous valleys where the warm weather and high humidity created a perfect environment for the disease to increase and spread. GLS has become a major problem across wide areas of the corn belt during the past three or four years.
Gray Leaf Spot, or GLS, is only known to affect corn. The symptoms of the disease vary with the severity of the infection and stage of corn development at which the infection occurred. The disease is first detectable as small grayish lesions on the lower leaves, which run parallel to the veins. As the disease progresses the lesions may coalesce (grow together) and cause the entire leaf to turn brown or gray. The lesions may also appear on the ear husks. Spores, commonly known as inoculum, that overwinter on the residue of the previous year’s crop spread the disease. Wind and surface water movements move these spores. In order to infect the plant, the GLS pathogen requires a moisture film on the corn leaf that lasts from twelve to thirteen hours or more. Then, if air temperatures remain in the 70 to 85 degree F range, the spores germinate and grow into the cuticle of the leaves. The disease moves up the plant with each successive generation. The disease can reach the top of the plant with as little as three generations. Once infected, the disease destroys the plant’s green tissue. This results in kernel abortion, shallower grain fill, reduced plant health, and reduced stalk and root quality. If the disease kills the leaf tissue late in its development cycle, the effect will be minimal. If the plants are infected early and a high percentage of the leaf tissue is lost for most of the growing season, yield losses could reach 30 to 50 percent.
As the advent of no-till and reduced tillage created higher residue situations over the corn growing area from Ohio to Nebraska, a perfect environment was created for inoculum to perpetuate itself from one season to the next. Plant pathologists also believe that the disease mutated slightly and became able to flourish under drier conditions. The climate in the western corn belt has changed since 1987 and many parts of Iowa and Nebraska now receive three to four more inches of rainfall than in the previous years. Pivot irrigation has become more popular in the more arid corn growing areas. The so called “opportunity time” mist emitted by the low pressure systems are also thought to create the 12 to 13 hour long moisture film on the leaves allowing entry by, and a rapid spread of, the foliar disease. True resistance to GLS is seen in some inbreds. However, none of these inbreds are currently being used in commercial hybrids. Currently, the best resistance is from inbreds developed in the southeastern states or from those deprived from tropical germplasm.
Chemical control of GLS is possible by applying one of several fungicides currently on the market with applications generally best around 5 days post tassel. Control of the disease to acceptable levels will take an effort on many growers’ part. The best defense against GLS is to plant hybrids with good GLS tolerance. This means that some corn producers may have to abandon their favorite hybrid. Good tolerance to GLS is available in different hybrids that also yield and perform well under other stresses. It is best to choose 3 to 4 hybrids of different genetics, and flowering dates, each containing good GLS tolerance. However, no hybrid is completely immune to GLS. If high levels of inoculum from the previous year, or an infected neighboring field are present, and weather conditions are perfect, even the immune system of a good hybrid can be overwhelmed. Therefore, the best management program should combine hybrid selection with a tillage program to bury the disease inoculum. All Hoegemeyer corn hybrids have a GLS rating listed in our seed guide as well as on individual hybrid tech sheets which are available on line at www.TheRightSeed.com
For some people, a soil analysis report can be somewhat confusing. There are all sorts of numbers and parameters on the report that are the numerical results of various tests performed on the soil. Some people find this information to be overwhelming because they don't know why certain parameters are tested. As you read through this publication, keep in mind that soil test results do not measure pounds available to the crop during the growing season, but rather the ability of the soil to supply nutrients to the crop. The following are explanations of the parameters measured in most soil laboratories of the Great Plains.
pH is an indication of the relative acidity or alkalinity of the soil. It is based on a logarithmic scale from 0 to 14, with 7 being neutral. Being a logarithmic scale each change of 1.0 unit is a 10x unit change. For example a soil pH of 6.0 is 10 times more acid that a pH of 7.0. A soil pH of 5.0 is 100 times (10x10) as acid as a pH of 7.0. Most row crops perform best, and a wider range of nutrients are adequately available, with a soil pH between 6.0 and 7.0. The buffer ph test is conducted to determine the amount of lime to apply in order to reach the desired soil pH. It does not represent the intended or target pH for that crop. This test is required due to the effect of the soil CEC (See below).
Organic Matter (OM)
Soil organic matter performs many beneficial functions in soil. It provides nutrients, holds water and improves soil porosity by preventing clay particles from sticking to each other. "Organic matter" to a soil scientist and as shown in soil-test reports does not actually include all organic material in the soil. It refers only to the stable, highly decomposed, tar-like organic material that gives soils a dark color. (However, soil does not have to be dark to have a significant amount of OM.) Organic Matter is usually given as a percentage of the total sample.
CEC stands for Cation (pronounced "cat-ion") Exchange Capacity. Cations are elements with a positive charge such as K+, Ca++, Mg++, Cu++, Fe++, Mn++, Zn++, Al+++, Na+, NH4 +, H+, and others. CEC is an indication of the soils ability to attract, hold, and supply cations to plants. Large CEC values indicate that a soil has a greater capacity and strength to hold cations. Therefore, it will be more resistant to a change in the soil test, or pH level. When the soil test level is good, it offers a large nutrient reserve. A high CEC soil also requires a higher soil cation level to provide adequate crop nutrition. Low CEC soils hold fewer nutrients, and will likely be subject to leaching of mobile nutrients such as nitrate nitrogen (NO3-N), sulfur (S), boron (B) and molybdenum (Mo). These soils may benefit from split applications of several nutrients. The particular CEC of a soil is neither good nor bad, but knowing it is a valuable management tool. Nitrate-N (NO3-N) Row crops show the greatest yield response to additions of Nitrogen sources. It is no surprise that this test is run on nearly all analysis of soils for row crop production. Nitrate-N (NO3-N) is the predominant form of Nused by most plants. It is an anion that can be lost through normal environmental soil conditions. Many variables can affect plant availability, so use caution if using a recommendation based on the level of nitrate reported.
Phosphorus is essential to many plant functions and is a component of genetic material. The common P tests were developed to provide an index of P available to plants under a variety of soil conditions. This index is reported in pounds per acre or parts per million (ppm x 2 = lb./A), depending on the report. Due to its strength in soils with calcareous parent material, the Olsen P test is commonly used west of the Missouri River though the Mehlich-3 (colorimetric) P test would do equally as well.
Potassium is a cation usually found in adequate amounts in the Great Plains soils. The amount contained in the sample is reported in either pounds per acre or parts per million (ppm), depending on the report format. Additional information may be reported as the percent saturation. Percent saturation is best described as the percent of the CEC that is occupied by the element. The desirability of a particular percent saturation for each of these nutrients is sometimes affected by other soil conditions and the plant species to be grown.
Secondary nutrients Calcium Ca, Magnesium Mg, and Sulfur (S), are not often lacking in soils that are formed from loess such as the soils of the Great Plains.
Secondary & Micronutrient Tests
Micronutrients are as important to plant growth as the levels of macronutrients in the soil. However, they are required only in very small quantities and are often supplied adequately by the soil. Of the micronutrient tests available, the results of Zinc, Manganese & Iron are the most valuable to soils of the Plains though instances of deficiency are rare. Sodium (Na) & Soluble Salts Because high levels of Sodium (Na) & soluble salts are generally damaging to plant growth, some labs run tests if this is a suspected problem. Sodium is reported both as parts per million (Na ppm) and percent saturation (Na Sat %). Soluble salts are reported as a measurement of electrical conductance of the soil solution called millimhos/centimeter (mmhos/cm). This value increases as the salt content of the soil increases.
Soil texture refers to the percent sand, silt, and clay contained in the soil. The proportions of these components determine the name assigned to the soil (sandy loam, silty clay, etc.) as shown in the USDA textural triangle. The name of the texture is reported in one column, with the percentages of sand, silt, and clay in the following 3 columns. This information has several applications, but is probably used most frequently to identify drainage characteristics of the soil.
Laboratories vary on how or if they choose to provide recommendations for amending the soil. Discussions of recommendations are beyond the scope of this document, but remember to be cautious to not interpret the soil test results as absolute figures when they are only an index. As stated before, soil test results do not measure pounds available to the crop during the growing season, but rather the ability of the soil to supply nutrients to the crop.
When Should Replant Be Considered?
The replant decision is a tough call. Things to consider in this decision include:
- Productive Plant Population: You will need to determine the productive plant population in several areas of the field to help estimate the potential yield of the field if left as is.
- Stand Uniformity: If the productive plant population is not uniformly distributed within the row, additional yield loss will likely occur.
- Original Planting Date: The original planting date plus the remaining productive plant population will be used to estimate the yield potential of the field.
- Likely Replanting Date & Target Plant Population: These will be used to estimate the yield potential of the replanted field.
- Likely Replanting Costs: The cost of replanting a damaged field often makes or breaks a replanting decision. Usual costs include seed, fuel (tillage and planting), additional pesticides, and additional dryer fuel.
- Expected 'Normal' Yields: Estimates of the yield potentials of the damaged field and the replanted field are based on a percentage of 'normal' yield for the field in question. Unless you are excellent at predicting yields for the coming year, consider using a five-year average.
- Expected Market Price for Corn: The dollar gain or loss by replanting obviously depends greatly on what you expect to receive for the grain this fall. The volatility of the grain market this year makes it especially difficult to plug in' a value for determining a replant decision. Use your best guess.
Row length equal to1/1000
acre for various row widths.
|Row width||Row length equal to 1/1000 acre|
To figure the plant population, use the chart above:
- Using the chart, find the row width of your planter
- Using the chart, determine how many feet it takes to make 1/1000th of an acre (example: 30” = 17’ 5”)
- At multiple locations throughout the field, count the number of remaining plants in 1/1000th of an acre lengths
- Average your 1/1000th of an acre counts
- Multiply the average of your counts times
- 1000 for the average population in the field
Corn plant skips or gaps in the field cause yield loss. Longer skips usually reduces yield more due to fewer plants, uneven plant placement or possible weed competition. The following chart lists the plant spacing at different row widths and plant populations.
- Corn plant spacing (inches) at four different plant populations and row widths
|Row width (inches)||Plant population|
Original Planting Date & Stand Compared To A Later Plant/Replant Date & Stand.
- Corn yield expressed as a percent of the optimum stand and date.
|Plant Date||April 20 to May 5||May 20||June 1||June 10|
|26,000 to 30,000||100||90||81||67|
* Assumes reasonably uniform stands. Source: G.O. Benson, Iowa State University
If Corn Plants Are 100% Defoliated At Different Growth Stages, What Is My Potential
The Perfect Hybrid There is no perfect hybrid that fits every situation or need. Therefore, when selecting those hybrids for your farming operation, you’re the one that must assess your farming operations strengths and weaknesses in order for you to properly evaluate the hybrids that have the
What Are Some Corn Hybrid Selection Factors to Consider?
Don’t put all of your eggs in one basket and plant one variety. No two years are the same and planting a portfolio of genetic backgrounds will give you diversity to help give you yield consistency from one year to the next.
Because you most likely can’t plant your entire crop in one day and in one field, chances are you will be planting in different weather conditions, soil types, soil temperatures, and overall environments. Plant the hybrids at the times and in the areas they can best handle.
Each hybrid has its most advantageous population at which it expresses its uppermost yield potential. Consider ear type and its interaction with the corn production system you use in your farming operation.
Ear types are either fixed or flex. With-in reason, fixed ear types make the same size ear regardless of population while flex ears can make either longer or girthier ears if competition is decreased by reducing population.
The less that you till the fields, the greater are the chances you will encounter cooler soil temperatures, wetter soils, and more residues which may well mean increased insect pressures at or after seed germination.
Continuous Corn or Rotation With Another Crop
Crop rotation tends to break insect and weed cycles. It could also help in reducing some of the residue buildup that possibly will be the host for insect and disease survival. Poorer stalk quality might also be a problem in many continuous corn on corn fields.
Dryland, Irrigated or Drought Tolerance
Hybrids that can flex in ear length or girth fit dryland or drought conditions better. Irrigated or adequate moisture situations are more manageable, so hybrids that can handle high populations, have high yield potential, or produce determinate ears are good choices.
Soil Fertility, Soil Type and Topography
Lower fertility soils get the best yield potential from flex ear type hybrids and varieties that do not need higher populations to produce yields. Another advantage of flex ear hybrids in lower fertility soils is at lower populations less vegetative matter is produced. Lower plant population means a smaller amount of vegetative matter is produced so fewer plants means less demand for moisture and nutrients needed from the soil. Topography, what’s the lay of the land? Canopy cover is advantageous to help conserve moisture and shadow out weeds. Consider the hybrids height when planting in hills or on poorer soil types.
Plant Growth Type (early or late flower for hybrid maturity)
Flowering or pollination in relation to length of grain fill is a yield consideration. Later flowering hybrids many times produces a larger stature hybrid, the grain fill period for yield potential is shorter, and yield may be hurt if a prolonged period of heat coincides with the shorter grain fill period. Shorter grain fill periods sometimes make softer kernels and lower test weights. Early flowering hybrids use longer grain fill periods to generate yields but plant stature may be smaller. Areas where heat could be a problem during grain fill choose to use early flowering type hybrids.
Stalk Quality and Root Lodging Resistance
Stalk quality is the ability of the plant to stand and stay intact through harvest. The two main sources of stalk quality are rind thickness and staygreen. It is not necessarily the diameter of the stalk, but the thickness of the rind that provides resistance to lodging. The rind is made of lignin and lignin provides the rigidity that keeps the plant upright into the harvest season.
Drydown and Grain Test Weight
Drydown, or the rate at which moisture leaves the kernel, is influenced by husk looseness, plant staygreen and test weight. Test weight is influenced by how staygreen a hybrid is. Hybrids that are fast-die and fast-dry are more apt to have lower test weights.
Corn Borer and Insect Tolerance
Hybrids differ in tolerance to corn borer. Hybrids that are planted early or grow fast early are more attractive to first brood corn borer. Later planted or immature corn is more attractive to second brood corn borer. If other insects are a concern, consider genetically altered varieties or ordering specific seed treatments for the varieties you choose.
Herbicide tolerant hybrids are becoming more popular and work well when properly applied and utilized. However, we also need to be good stewards of herbicide use and understand that we still need to rotate herbicides. Good stewardship will help delay weed resistance to a herbicide and prolong its overall effectiveness. According to the chemical company’s representatives, no new herbicides are on the horizon. If we abuse the herbicides we are using today, and resistance becomes a problem, there is not a new lifesaving herbicide waiting to replace it!
Stalk rot seems to show up every year somewhere. The pictures you see are some of the more common stalk rots that may be found out in a corn field. Several fungi and bacteria can cause stalk rots both earlier and/or later in the season. Generally though, most stalk rots will show up later in the season.
Disease development is generally initiated by an early environment that favors kernel set followed by a late environment that is stressful such as (a) lack of moisture (b) nutrient imbalance or deficiency (c) excessive cloudiness (d) nematode, rootworm or other insect damage, (e) hail or other mechanical damage to the leaves, stalks or roots (f) loss of leaf tissue (g) excessive plant population (h) extended periods of very wet or dry periods (i) abrupt weather changes especially several weeks after silking. Other factors associated with stalk rot development include (j) high yields, (k) high N levels associated with low potassium levels, (l) high levels of decaying plant residue and (m) other plant diseases and stresses.
Balanced soil fertility is very important especially when it comes to potassium levels. Research has also shown the importance of adequate nitrogen during the entire season and how it can help reduce the severity of stalk rot. Take this into consideration, especially if nitrogen leaching or denitrification has occurred during the growing/grain production season. Most importantly, do not guess on the fertility needs of your field. Fertilizer application rates should be based on the results of soil tests. Soil tests may save you money in the long run via establishing the fertility needs and limiting excess fertilizer costs and helping to promote better plant health if the correct nutrient rate/balance is provided.
Hybrids vary in many ways and a producer needs to better understand the hybrids he has chosen to grow. Population in some cases may be the major culprit for a stalk rot problem with a hybrid. Some hybrids when planted at excessive rates can result in spindly stalks with reduced standability that may promote stalk rot which in turn probably means yield loss.
Stalk rots cannot be completely controlled but damage can be reduced. Here are several food for thought items to help reduce stalk rot influenced harvest loss. (a) Understand the hybrid you are growing and the capabilities it has, (b) follow a balanced fertility program, (c) control insects (d) plant at the proper rate (e) if you irrigate, avoid putting stress on the plants (f) foliar disease prevention can help with stalk rot potential associated with fungus and (g) good weed control.
Check your fields to make sure that stalk rot will not be a problem. Hybrids that have a thicker rind or other complimenting characteristics may not appear to have stalk rot but they may. Squeeze stalks above ground level to make sure they are not hollow or diseased. If some are hollow, this might be a field which you may want to consider harvesting sooner rather than later.
What is Stalk Rot?
Corn stalk rot is a family of diseases caused by several species of fungi and bacteria. Severity of the disease changes from year to year due to climatic conditions, agricultural practices, hybrid genetics and stresses such as available water, fertility, plant population, foliar diseases, insect damage and weed competition. Stalk rot causes internal decay and discoloration of stalk tissues which directly reduces yield and standability by impairing water and nutrient uptake which can result in lodging and pre-mature death.
What Are Some Stalk Rot Symptoms?
The two most striking external symptoms are pre-mature death and stalk lodging. Visually, the leaves may appear to turn dull to grayish green while stalks, depending on which stalk rot is developing, may show brown or black or pinkish-red internal and/or external discoloration. A major portion of the pith tissue is usually destroyed and the remaining strands of vascular bundles inside the stalk are usually discolored. Advanced stages of stalk rot leave the stalk spongy, soft and hollow.
When is a Corn Plant Most Susceptible to Stalk Rot?
Stalk rot, in one form or another, can attack the plant as early as the seedling stage or any time there after. The seriousness of stalk rot is dependent on the types of stresses and the timing when these stresses impact the plant. To date, no true stalk rot resistant hybrids are available however; hybrids vary greatly in tolerance to stalk rot. Foliar diseases increase the severity of stalk rot by impairing leaf tissue thus reducing the amount of photosynthetic activity that can be done by the plant for nutrient manufacture, grain production and acrossthe- board survival. Yield is reduced because the plant draws on stored nutrients in the stalk for survival which otherwise would have been used for grain fill / production.
What Are Some of the Most Common Stalk Rots?
Fusarium Stalk Rot is one of the most common stalk rots. Its pathogen survives on crop residue and in the soil. Fusarium infects the plant by the pathogen being splashed on the leaf and washing down the leaf into the sheath and infecting at the nodes. It can also infect directly through the roots causing decay in the roots or lower stalk. Wounds from hail or insect feeding can provide additional sites of entry. Fusarium stalk rot along with Gibberella stalk rot produces a reddish-pink discoloration on the internal stalk tissue.
Gibberella Stalk Rot, which is a pinkish color too, also survives on plant residue or in the soil. Wind blown spores are dispersed to stalks and infect by direct penetration. Infection may also occur through the roots, wounds on the stalk and leaf scars. The spores can also be splash-dispersed and infect the ears and kernels.
Diplodia Stalk Rot usually occurs three to six weeks after silking. It Is distinguished by internal brown stalk discoloration and dry rot in the lower two internodes of the plant. The pith tissue is usually shredded and black spore forming structures are commonly found on the surface of the lower stalk. Spores can be transferred by wind, rain and insects. As the disease progresses, small brown / black reproductive structures form on the stalk surface near the nodes. Anthracnose Stalk Rot has three components (A) leaf blight (B) stalk rot (C) top die back. Prolonged periods of high temperatures and humidity are conducive to this stalk rot. Top die back occurs mid to late summer and affected fields appear to have a green band across the middle of the plants because the lower leaves are drying up due to normal senescence and the upper leaves are dying from anthracnose. Anthracnose has black discoloration on the inside of the stalk as well as on the surface.
Charcoal Stalk Rot is caused by a fungus which attacks the roots, enters the crown and eventually disintegrates the pith leaving only the vascular bundles. Numerous small dark specks called sclerotia form on the bundle strands and can easily be seen when the stalk is split. Sclerotia develop in dry areas where soil temperatures are high and soil moisture is low.
Pythium Stalk Rot occurs under warm wet conditions. Unlike most stalk rots which occur after tasseling, Pythium stalk rot can appear at any time. The rind and pith may become soft, brown and water-soaked and the decayed tissue may have a strong odor. The stalk typically twists and falls over, but the plant may remain green for several weeks because the vascular tissue is not destroyed. Pythium stalk rot may also cause top die back.
What is Test Weight? Test weight of corn determines the weight of a bushel volume (1.244 cubic feet) of grain. Test weights determined on dry (15.5% moisture) corn can indicate whether the grain crop reached full maturity. Low test weights indicate immaturity. The minimum test weight for USDA No. 2 corn is 54 pounds per bushel.
What causes low Test Weight? When we speak of test weight, we are more specifically talking about the accumulation of starch in the kernel during grain fill. Grain fill and thus test weight may be adversely affected by early frost, drought, high temperature, nutrient deficiency, disease or insect injury, shading, hail damage, overpopulation, and other stress factors. The relationship of stress and test weight is most severe during the early stages of grain fill and lessens as the starch levels get closer to full accumulation (black layer).
How does low test weight affect me? In most cases it is assumed that a higher test weight is better when comparing similar maturity hybrids. Wet millers and dry millers choose this attribute for quality purposes, as do feedlots for livestock feeding value. University research from Minnesota has shown that the effects of low test weight corn (<54#) are minimal on feed value. Due to this and other similar findings, feedlots should continue with full season hybrids and put less emphasis on test weight. Elevators and processors will dock based upon test weight, particularly when the weight falls below 54 pounds per bushel. They do this for a variety of reasons; higher transportation costs, lower milling quality, greater potential for mycotoxins and storage problems
Table 1. Grain corn test weights and potential dockage.
|Grade||Test Weight Minimum (lb/bu)||Potential Dockage $/bu|
Table 1 outlines potential dockage that growers may experience when delivering lower bushel weight corn to an elevator or processor. (Note: these discounts will vary fromelevator to elevator and from year to year and are provided as an example only.)
What, if anything, should I do if I’m concerned about low test weight? Producers who deliver all of their corn to elevators or processors may want to switch to earlier hybrids to increase the potential for suitable test weights at harvest. Producers in shorter season areas who fear significant yield losses by switching to earlier maturing hybrids may consider staying with full season hybrids but switching to hybrids which have higher test weight scores. Test weight concerns should also be taken into consideration when selecting hybrids for planting in a delayed spring.
WESTERN BEAN CUTWORM IN CORN
Western Bean Cutworm (WBC) and the potential devastation this pest can inflict on cornfields is becoming a more urgent concern for Western Cornbelt producers. There is also an increased awareness that detection of and protection from this pest is difficult. By knowing more about the WBC’s history, life cycle, physical damage and economic loss, top producers can minimize the impact by this pest.
The WBC is native to the high plains region of the United States, where it was documented as a pest in dry beans years ago. Sometime in the last half-century, the pest developed an appetite for corn and migration to cornfields to the east was inevitable. The WBC adult moths prefers lighter soils when overwintering but have been known to cause economic damage anywhere west of Interstate 35 in Iowa. This leads entomologists to believe the WBC has adapted to laying eggs in finer soils or flight distance is much greater than previously thought. All field corn in the western cornbelt without an in-plant insect-protection trait like Herculex™ I * should be scouted beginning in mid-July. Field corn in the Western Cornbelt has traditionally been treated with a broadcast liquid insecticide.
Depending on the number of heat units accumulated during a given year, the WBC moths can usually be found in light traps in early July. Scouting for egg masses on upper leaves and larvae in the tassels and silks starts in mid-July. The eggs are pumpkin-shaped and become purple when hatch is close. Magnification of the egg mass is necessary for initial identification. Once hatched, the larvae move from the whorl to the tassel. Silks soon follow and the WBC quickly migrates to the ear where insecticides are not effective. The larvae start out dark brown and become lighter with each growth stage until reaching a pinkish-tan color. The larvae are often confused with Corn Earworm that have similar features and occupy corn silks and ears at the same time. Damage and management of these two insects is not the same, so correct identification is important.
In the ear tip, the WBC increases in size over several weeks. Nearly all of the damage is done by the last stages of the larvae by the grain they consume and the diseases they introduce. In the final stage of larvae growth, the larvae are over one inch in length and have an amazing appetite for their size. In addition, the WBC has no problem sharing thesame ear with many other WBC larvae unlike the Corn Earworm which is cannibalistic and generally less destructive.
While WBC is not a serious problem in every field every year, the occurrence of economic loss has been increasing. Warmer, dry winters and/or winters with snow cover keep the over-wintering population high. Documented losses of several bushels per acre have been found when an average of one WBC per ear and it is common to find more than one larvae per ear.
Most University extension departments agree that the threshold level is between five and ten percent egg masses found. However, even professional agronomists will admit to having problems pulling the trigger on treatment. It takes sampling many locations in a field every few days to stay on top of this insect. To make matters worse, insecticides miss those cutworms protected by ear husks and latecomers that have not yet hatched. Herculex™ I * technology mentioned earlier takes care of the timing problems broadcast applications have by providing full season protection of the Western Bean Cutworm. Though the protection is not one-hundred percent, it is high enough to offer a substantial improvement over the downfalls of broadcast insecticide treatments.
*Herculex I Insect Protection technology by Dow AgroScience and Pioneer Hi-Bred. Herculex is a trademark of Dow AgroSciences LLC
THE AUTHOR DOES NOT GUARANTEE THE ACCURACY OF THE INFORMATION CONTAINED IN THIS FEATURE, ALTHOUGH IT IS BELIEVED TO BE ACCURATE. THE AUTHOR ASSUMES NO LIABILTY OR RESPONSIBILITY FOR DIRECT OR INDIRECT, SPECIAL, CONSEQUENTIAL OR INCIDENTAL DAMAGES OR FOR ANY OTHER DAMAGES RELATING OR ARISING OUT OF ANY ACTION TAKEN AS A RESULT OF ANY INFORMATION OR ADVICE CONTAINED IN THIS REPORT. THE AUTHOR DISCLAIMS ANY EXPRESS OR IMPLIED LIABILITY OR RESPONSIBILITY FOR ANY ACTION TAKEN, WHICH IS SOLELY AT THE LIABILITY OF AND RESPONSIBILITY OF THE USER.
CREDITS: University of Nebraska Cooperative Extension, Western Bean Cutworm in Corn and Dry Beans, publication G98-1359-A
Colorado State Universtiy Cooperative Extension, Western bean Cutworm: Characteristics & Management in Corn and Dry Beans, publication 5.538