Posts Tagged ‘field corn’

Corn and Corn Silage Dry Down Rates

Friday, August 24th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

I was asked this week about how fast corn dries down. The first question was about corn silage. Actual dry down rate varies depending on factors such as air temperature, solar radiation/day length (whether in August, early- or late-September, or October), hybrid, soil moisture levels, and a host of other factors. Most sources report an average drying rate of 0.5 percentage points per day during the month of September although the average rate by year has varied from 0.4 to 0.7 percent per day. If you look at the daily dry down rate within a given year, the rate varies tremendously from as little as 0% per day to as much as 1% in a given day. So for silage even though the average rate is 0.5% per day since making good silage is so dependent on having just the right amount of moisture so the silage will pack well and will ferment properly, you will need to watch your corn very carefully and do frequent checks to ensure the corn does not get too dry.

For grain, a number of factors impact the rate of dry down and these include weather, hybrid, maturity group, planting date, accumulated growing degree days or heat units, and husk and ear characteristics such as husk leaf number, thickness, and tightness of wrap and ear position (drop) and length protruding from husk. By far the most impact occurs with the type of weather we experience in any given fall. In years when the weather is cool and rainy, dry down will be very slow, perhaps less than 0.3% per day. In years where we have warm days, dry conditions, and plenty of sunlight, kernel dry down can reach 1% per day.

Dr. Bob Nielsen with Purdue University has studied the many factors involved in corn dry down and reports that the average daily dry down rate can range from about 0.8 percentage points per day for corn that nears black layer (physiological maturity) in late August to about 0.4 percentage points per day for corn that does not reach maturity until mid- to late-September. Although monitoring grain moisture loss is not quite as critical as with corn silage, we do know that harvest losses do increase as grain moisture falls below about 18 to 22%. With grain prices quite high, minimizing losses by harvesting when grain moisture is still slightly high can pay a healthy premium as can making adjustments to your combine to ensure the most efficient grain recovery possible.

Problems With Corn Seedlings This Year

Friday, June 1st, 2012

Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

Uneven stands have been seen this spring in corn fields. Corn seedling issues have been attributed mostly to environmental conditions, including dry soil at planting, resulting in variable depth of seeds and uneven emergence. Our early May weather resulted in wet, cool soil conditions conducive for fungi that invade young seedling roots and mesocotyls. Stress brought on by recent hot weather has exacerbated stress on seedlings. A recent article from Purdue University highlighted some issues also seen in the Midwest that apply to corn in Delaware:
http://extension.entm.purdue.edu/pestcrop/2012/issue8/index.html#seedling

Sulfur Deficiency in Corn

Friday, June 1st, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

After visiting a great many fields over the past few days, I came to the conclusion that our efforts in controlling air pollution and especially sulfur (S) emissions have been very successful, perhaps too successful. The number of corn fields that are showing areas that of yellowing plants likely due to S deficiency is as great as or greater than I can ever remember seeing. I’m seeing plants with both the traditional S deficiency we all learned about in school where the plant shows a general chlorosis and stunting (Photo 1) and interveinal chlorosis that has been the hallmark of S deficiency in the past few years (Photo 2). Although many agronomists in the area were unsure of the interveinal chlorosis symptomology when it first appeared, Dr. Greg Binford did a few fertilization studies that seemed to confirm that S was responsible for the symptoms or at least could eliminate the symptoms.

Photo 1. More traditional sulfur deficiency symptom on corn with general chlorosis of the leaves and stunting of the plant which was about half the size of less affected plants.

Photo 2. Less traditional sulfur deficiency symptom on corn with severe interveinal chlorosis of the leaves along with stunting of the plant.

Many growers are already taking steps to reduce the impact of the ‘cleaner air’ by adding some ammonium sulfate to the corn starter fertilizer or to their sidedressed nitrogen (N). In Dr. Binford’s field trials, he did get a yield increase when S fertilizer was added; although in studies a number of years ago, I didn’t find a yield response to added broadcast S fertilizer. In many cases as the corn root system continues development, it is able to pick up S from the deeper soil layers and the deficiency symptoms disappear on their own accord. Another complication in the story is that we have changed from using the old superphosphate fertilizer (rock phosphate treated with sulfuric acid to make a 0-20-0 fertilizer) to new formulations, MAP, DAP and ammonium polyphosphates. This change has reduced the amount of S we were adding to our soils without consciously realizing it. I think as we go forward more and more growers will be using ammonium sulfate at some point in their cropping rotations to add needed sulfur to the topsoil.

You should keep in mind that S is either in an anion (negatively charged ion) form (SO42-) or is rapidly converted in warm, moist soil to the anion sulfate form. Anions such as sulfate and nitrate are subject to leaching loss from the topsoil. Dr. Tom Sims did find large quantities of sulfate in the deep subsoil layers of even the sandy soils in Sussex County, Delaware but the corn and other crops are not able to obtain S from these layers until much later in the growing season when the root system is nearly fully established. Early in the season, we are likely to find more and more fields showing S deficiency unless S fertilizer is regularly applied to the crops.

Look at Those Early Planted Corn Fields

Thursday, May 3rd, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Some of the earliest planted corn fields were sprayed with preemergence herbicide, but then had 7 to 10 days without rain to activate them. You need to check to those fields for emerging weeds and be prepared to spray earlier than you may have expected. Also, I have seen more yellow nutsedge this year than I have in the past few years. So be sure to identify those “grasses”, and be sure you know what grass species it is or whether it is nutsedge.

Early Planted Corn Risk

Thursday, April 5th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

The warm late-March air temperatures and reports of soil temperatures in many locations well above the minimum 50º F required for corn to begin the germination process have encourage a number of growers, especially those with many acres to plant, to get an early jump on corn planting season. Recently the weather pattern has brought in cold air over our region and some areas are experiencing frost, albeit light frost. If even colder air arrives, early emerging corn may be frost injured. Until the corn’s growing point extends above the soil surface, corn often grows out of frost or freeze injury, although some minor yield reductions may occur. In the past we have seen such severe leaf injury on no-till corn which was at the third to fourth leaf stage that the growing point was unable to recover. This resulted in very thin, weak stands. It was thought that so much leaf tissue was killed that the decay process caused free-radical formation which overwhelmed the ability of the growing point to survive.

I point this possibility out so growers will be aware that there is a greater risk that more of the early planted corn fields will need to be replanted. I understand that the seed supply, especially for the better hybrids, will be very limited this year due to unfavorable weather conditions in Argentina where a lot of our seed corn is grown. Although growers who need to replant may be able to find replacement corn seed, it is likely that the best genetics will not be available. This fact should be kept in the back of the grower’s mind when planting early.

Burndown No-Till Fields

Friday, March 30th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Fields that will be planted to no-till corn or soybeans may have excess weed growth due to the warm winter. This will make burndown treatments more challenging, and in some cases it is unrealistic to expect complete control with only one application. In those cases, you may need an application now, followed by an additional application at planting. For weeds that are hard to kill with glyphosate, additional herbicides such as 2,4-D can enhanced the control (for instance, mustards); while other herbicide combinations can reduce glyphosate control (for instance, atrazine in combination with glyphosate for ryegrass control). Be sure to assess each field, and determine the best approach. Do not assume you can spray a week ahead of planting and achieve a clean seedbed to plant into.

Corn Herbicide and Soil Insecticide Interactions

Friday, March 30th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Last year a few farmers had severe corn injury because they had used an organophosphate insecticide and an ALS-inhibiting herbicide at planting. Remember, there a number of corn herbicides that have label precautions about use when an organophosphate insecticide is used at planting. The herbicides include both soil-applied and postemergence herbicides. This includes the insecticides Counter (terbufos), Lorsban (chlorpyrifos), and Fortress (chlorethoxyfos). The list of herbicides is quite extensive and includes multiple herbicide families so follow this link for a detailed list of herbicides http://www.rec.udel.edu/weedscience/CornGuideWeb/CornLinks/CornTable19.pdf

Unfortunately, most corn seed companies no longer designate hybrids as either IT or IR. So if you are not sure, take the cautious approach and assume the hybrid is a “standard” hybrid (no enhanced tolerance for imidazolinone herbicides); and follow the most restrictive guidelines.

Seed Corn Maggots Control in Field Corn

Friday, March 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

With the warm winter conditions, we have observed flies actively laying eggs earlier and for a longer period of time. Adult flies are active in temperatures down to the mid 40s so it very likely that maggot populations could be higher in early planted field corn. Conditions that favor egg laying activity include decaying cover crops, high organic matter, freshly plowed fields, and/or manure applications. Control options include commercial applied seed treatments, or soil insecticides. It should be noted that seed treatment labels indicate that they only provide early season protection of seedlings against injury from seed corn maggots.

Dealing With Corn Ear Rot Infected Grain

Friday, September 23rd, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

We continue to get samples of stalk rot, and now ear rots in field corn. More samples of Fusarium ear rot caused by Fusarium moniliforme also known as Fusarium verticillioides have been received in the diagnostic lab this week. Hybrids that have been holding their ears vertical and have poor ear cover can be more susceptible to ear rots that benefit from moisture trapped in the ears. Ears that have been damaged by insects, particularly corn earworm, can also have more ear rot fungal infections. Fusarium moniliforme can produce mycotoxins called fumonisins.(see below), but not all isolates of the fungus produce fumonisins. Infected grain should be dried to 15% or below to prevent mold growth in storage.

When evaluating an ear rot problem, remember that certain ear rots are a warning sign to suspect toxins, but ear rots do not always lead to toxin problems. When potentially toxigenic ear rots are noticed in the field, grain can be managed to minimize toxin development. If more than 10% of ears have a significant amount of mold (25% of the ear or more), these fields should be harvested and the corn dried as soon as possible. The combine will remove some of the moldiest kernels.

Fusarium ear rot caused by Fusarium moniliforme

The best option for moldy grain is to feed it or sell it instead of storing it. However, it should be tested for toxins before feeding. Testing for mycotoxins can be done before putting the grain in storage. The best sampling method is to take a composite sample of at least 10 pounds from a moving grain stream, or to take multiple probes in a grain cart or truck for a composite 10-pound sample. If toxins are present, it is possible that it can be fed to a less sensitive livestock species, such as beef cattle (depending on the specific toxin and its concentration). A veterinarian or extension specialist can help with these decisions. If the grain is sold, there may be a reduced price due to mold damage.

Cleaning the grain removes fine particles that are usually the moldiest and most susceptible to further mold development. Good storage conditions (proper temperature and moisture content, aeration, insect control, clean bins) and regular inspection are essential in preventing mold and toxin development in any stored corn. G. Munkvold (Iowa State Univ. Ext.)

Charcoal Rot Identified in Corn

Friday, August 26th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Charcoal rot was identified in corn this week. Charcoal rot caused by the fungus Macrophomina is a common disease in soybean during hot, dry seasons. Occasionally it is seen in corn causing a stalk rot that in the early stages can look like the common stalk rots that we see here such as Diplodia, Fusarium and Giberella stalk rots. However when the stalk is split the characteristic sign of charcoal rot is the abundant small reproductive structures (sclerotia) inside the rind, especially on the vascular bundles. The inside of the stalk especially the lower 3-4 nodes are gray black giving it the name charcoal rot. Hybrids that have good resistance to other stalk rots often have some resistance to charcoal rot but the hot, dry conditions and early senescing of stalks can lead to infection and symptom development. Harvest in a timely manner to avoid lodging problems.

Charcoal rot on corn. Note the black sclerotia attached to the vascular bundles in the pith. That is the best diagnostic feature for identifying charcoal rot.