Agronomy Notes

October, 2002

Contents:

CORN
WHEAT
SOIL and NUTRIENT MANAGEMENT
SOIL TESTING
RICE
SOYBEANS

CORN

Dr. Erick Larson

Addressing Fertility Problems - Fall is the best time of year to address many fertility problems. Soil acidity is a perennial problem due to our warm, rainy climate. Applying and incorporating lime during the fall allows pH neutralization before crop growth begins. This will also improve nutrient availability. The increasing use of corn in crop rotations has also contributed to phosphorus and potassium deficiencies. Phosphorus deficiency is especially prevalent when corn is grown following a rice crop, because the absence of a flood reverts soluble ferrous phosphates to unavailable ferric phosphates. Thus, considerable phosphorus application is required to overcome this phenomenon. Phosphorus deficiency also often occurs following cotton or soybeans, because corn requires double the amount needed for cotton or soybeans. Potassium deficiency often occurs following a high-yielding soybean crop, since 70 bu./a. soybeans remove about 100 pounds of potassium from the soil. Yearly soil testing generating recommendations for corn will prevent these problems. Thus, take soil samples this fall, so that incorporation and neutralization of lime and broadcast fertilizer may occur before next spring. However, delay application of potassium on low CEC soils until spring because of leaching problems.

Fall Corn Borer Control - Southwestern corn borers overwinter as larvae underground inside the extreme base of the corn stalk. Disruption of this site using various tillage practices will theoretically reduce the survivability of larvae during the winter. Thus, producers with corn borer infested fields should consider this opportunity to alleviate next year's problem. Discing is considered the most effective (disruptive) treatment, due to its cutting, shredding and turning activity. Stalk shredding is ineffective, since the Southwestern corn borer larvae are underground, inside the base of the corn stalk.

Fall Weed Control - Fall is the best time to reduce populations of some tough perennial weeds, including Johnsongrass and Bermudagrass. These perennial weeds are most susceptible to chemical application at this time of year, because they are storing energy in their rhizomes in preparation for winter. A translocated herbicide, such as Roundup or Touchdown, will be drawn into the rhizomes and have a higher likelihood of killing these reproductive organs. Chemical applications should be made when weeds are actively growing and at least two weeks before the normal first frost date. Tillage or stalk shredding should not be done after harvest, unless Johnsongrass has time to regrow to the boot stage. Successive tillage after chemical application should preferably be delayed 4-6 weeks.

WHEAT

Dr. Erick Larson

Keys to High Yields: Drainage and fertility are two extremely important factors governing wheat yields which should be addressed in the fall. Wheat is grown during the rainy season, potentially exposing it to saturated conditions at any time. Thus, field selection and physical improvements, such as multiple surveyed water furrows and clean ditches, capable of improving drainage should enhance wheat yield potential tremendously. Because wheat is a relatively inexpensive crop, growers often overlook fertility needs with the exception of nitrogen. Wheat is a very shallow rooted crop grown during the wet season, making it nearly impossible to mine nutrients from the soil profile, particularly if substantial amounts of mixed fertilizer have not been recently applied. Thus, growers will likely need to supply enough phosphorus and potassium to meet crop uptake and correct soil pH, if needed, or yields will suffer.

Don't Plant Wheat Early: Early planting unnecessarily exposes wheat to potential development, fertility, weed and numerous pest problems which ultimately reduce yield potential. Early-planted wheat may proceed past the tillering stages (when it is most tolerant of subfreezing temperatures) before winter induces dormancy, particularly during a warm winter. This substantially increases the likelihood of winter or spring freeze damage and nitrogen deficiency related to excessive fall development. Early planting also promotes infestation of insects and disease infection by increasing exposure. Lush vegetative development encourages fall infestation of aphids, Hessian fly and Fall armyworm. Aphids vector Barley yellow dwarf, a disease which stunts wheat development and may cause substantial yield reduction, particularly from fall infection. Fall infestations of both Hessian fly and Fall armyworms may destroy stands. Hessian fly also cause broken stems and lodging in the spring. The development of Take-all, a fungus which prematurely kills plants by rotting the lower stem and root system, is also encouraging by early planting. Early planting promotes winter weed problems by allowing the entire winter weed seed bank to potentially emerge and compete with the wheat crop. Delayed planting allows a flush or two of winter weeds to germinate before planting commences. Thus, producers may control these weed flushes with fall tillage or burndown herbicide application to reduce the potential weed population. This is particularly important for hard to control winter annual grass species, such as ryegrass and cheat.

Optimum Planting Dates: The suggested wheat planting dates (within 10-14 days of the average first frost date in the fall) should provide warm enough temperatures and long enough days for seedling emergence and tillering to begin before dormancy occurs. This normally corresponds to:

  • North and Central Mississippi: October 15 - November 10
  • Delta Region: October 20 - November 15
  • South Mississippi: November 1 - November 25
  • Coastal Region: November 15 - December 10

Seeding Rates: Wheat growers should strive to establish 1.0 to 1.3 million plants per acre or 23 to 30 plants per square foot. Assuming 85% successful emergence planting with a grain drill, you will need a seeding rate of 1.2 to 1.5 million seeds per acre. Using the number of seeds per pound listed on the seed tag, you can then calculate how many pounds of seed per acre are needed. For example, 1.35 million seeds per acre divided by 13,500 seeds per pound is 100 pounds of seed per acre. This seeding rate is equivalent to 18 seeds per foot with a seven inch drill spacing. If planting with a drill is not feasible, assume about 70% emergence with broadcast seeding, combined with mechanical incorporation, or 55% emergence with aerial/broadcast seeding.

SOIL and NUTRIENT MANAGEMENT

Dr. Larry Oldham

DATE TO REMEMBER: Agronomic Professional Continuing Education Workshop, February 10-13, 2003 at the Bost Extension Center, MSU Campus, Starkville.

If a change in soil management system is planned, such as changing row spacing or adopting less intensive tillage, fall is the time to lay the foundation. One disadvantage of following some recently published recommendations on flooding fields for ducks is the loss of timely field work in the spring. We are only blessed with a few days to get a lot done when spring comes, and waiting for heavy clay to dry is very frustrating. As always remember to follow your soil test recommendations. Fall applications of phosphorus and potassium can be done on soils with CEC's greater than 8. There is likelihood that potash applied on very low CEC soils may be lost by leaching. However, again if the soils are to be flooded for any length of time, do not apply phosphorus in the fall. We only get about 10 to 20% efficiency with phosphorus fertilizers in the best of situations. "Flooded soil syndrome" is phosphorus deficiency in grass crops following a flood. It is common in Mississippi corn planted following rice. It often takes a full year or more non-flood conditions or banded phosphate fertilizers, even in high testing soils, to recover. It has been less of a problem in the more common rice/soybean rotation, but questions have risen about phosphorus fertility in the rice crop. Dr. Tim Walker is very actively addressing those issues through on-farm fertility experiments.

SOIL TESTING

Dr. Keith Crouse

Pelletized lime is a very fine ground limestone material that is pelletized with the aid of clay or synthetic binders to typically provide pellets in the 5 to 14-mesh range. Pelletized lime is made up of a very fine ground limestone material (finer than 100-mesh). That means it is a relativity fast acting material. However, some recent research has shown that some synthetic binders may inhabit dispersion of the pellets. This could cause an increase in the amount of time it would take to neutralize an acid soil. An advantage of pelletized lime is that it is easier to spread compared to pulverized aglime.

One ton of a typical aglime contains about five hundred pounds of particles finer than 100-mesh that bring about rapid soil pH change, and the rest of the other particles provide medium and long term acidity neutralization that prevents the need to relime each year. These particles of aglime, finer than 100-mesh, are used to make up pelletized lime. Even though each ton of aglime has about five hundreds pounds of fine material (finer than 100-mesh), that doesn't mean that five hundreds pounds of pelletized lime has the same neutralization value of one ton of aglime.

For most crops, lime should be incorporated into the top 5 to 6 inches of the soil, preferably at least 3 months in advance of planting. MSU-ES Soil Testing Laboratory's lime recommendations assume that limestone being used has a calcium carbonate equivalent (CCE) of 100 %. Remember, that Mississippi has two limestone grades A and B, which also determine the amount of lime needed.

RICE

Dr. Joe Street

Rice harvest was going well until hurricane Isidore arrived. The excess rain will probably reduce the quality of the late rice. Overall, early rice yields are higher than last year's record breaking yields. Some growers are reporting exceptional yields approaching the 200-bushel mark. It is too early to tell what the state average will be but it should be better than last year if we can get the down rice without significant yield loss. Quality of the early crop is good. Milling yields have been above average and pecky rice has not been a problem except in a few situations. Stinkbug damage was low during the early part of the heading period but the population increased in the later rice and caused significant damage in some rice. In a few situations, rice had spouted in the head prior to Isidore and that may increase if the temperatures remain warm.

With lodged rice, a harvest desiccant may be needed and the only approved harvest aid is Sodium Chlorate. From what I have seen so far, only the top layer of straw will be in contact with the Sodium Chlorate so about 3 pounds is sufficient to dry that layer of straw. At any one time, treat only what you can harvest within a three-day period

According to the county acreage survey, about 268,000 acres of rice were planted in 2002. The USDA revised their acreage down to 243,000 acres but that was not reflected in the county survey. The acreage survey indicated that 68 percent of the acreage was planted to Cocodrie with 16 percent in Priscilla, 6 percent in Lemont and 5 percent in Wells. Other varieties planted included Clearfield,

Cypress, Dixiebelle, Hybrid, Jefferson, and Saber. Last year, Lemont was planted on 60 percent of the acreage but Cocodrie replaced it as the most popular variety in 2002.

Red rice was more prevalent this year than in recent years. This could have been due to the cool spring, which prohibited early canopy closure and allowed more red rice to germinate. In some cases, the burndown treatment did not provide complete control of red rice. In general, the Clearfield rice system worked well for red rice control. However, there were some situations with marginal results. Soil moisture is critical for effective results with Newpath. If you had a red rice problem, consider planting Clearfield rice next year. At this time, CL 161, the most Newpath tolerant Clearfield variety is not yet approved. Approval is expected at any time. CL 161 is the highest yielding Clearfield line; however, it generally yields less than Cocodrie. Clearfield rice is the best option for dealing with red rice.

SOYBEANS

Dr. Alan Blaine

Although it seems like only yesterday that this crop went into the ground, the 2002 growing season is rapidly coming to a close. As of late-September, Mississippi was approximately 50 percent harvested. The September crop report has predicted a 33 bu/a crop. This is near a record high for us, but this estimate is low, and final yield for the state soybean crop could be in the high 30's.

Even going on record as the best crop ever, it has not been void of problems. Some things that have caused concern are: 1) Group IV's remaining green, 2) late season diseases: frogeye leaf spot, late season cercospora, SDS (Sudden Death Syndrome), stem canker, charcoal root rot, phytopthora and phomopsis, 3) irrigation problems 4) fertility problems, and 5) widespread insect pressure. I will attempt to address these problems briefly in this article and in more detail over the next few weeks.

Every year we experience varying disease problems, but this year we saw more than usual. Frogeye leafspot and late season cercospora were very widespread are the worse we have seen since in the late 80's. Late season cercospora has been positively identified as the cause for the discoloration and spots many have observed on Group IV's. It caused premature leaf drop which contributed to shriveled seed.

The hill area of the state experienced a fairly widespread problem with SDS (Sudden Death Syndrome). Although this disease pops up from time to time, it is normally more devastating in the mid-west than in the mid-south. An exception to this is irrigation of an extremely susceptible variety. SDS can be much worse in the presence of cyst nematodes, a concern for predominately hill growers. Normally when you see SDS in Mississippi it is an indication of an above average crop. It occurs under high anagement/excellent growing conditions. Most producers observed this disease on early planted Group IV's, predominantly on a susceptible variety. This scenario will not occur most years, but if it caused you concern, choose a more resistant variety and be sure to sample fields this fall for the presence of cyst nematodes.

Late in the season, we saw charcoal root rot show up mainly in dryland fields. Charcoal is a stress type problem. When you go from one extreme to another, it will express itself. No known resistance exists to charcoal. Although we had above average rainfall most of the season, dry weather over the last month was just what was needed for Charcoal to show up. It is by far the number one disease in the mid-southern United States and hopefully in the future its effect can be minimized.

Irrigation/drainage problems plus a cool, wet May caused phytopthora to rear its head. It was not widespread, but showed up where irrigations were delayed or drainage was not adequate. This was worse on the early planted part of the crop. Too many of us are still trying to water based on the calendar not the crop needs. In the south delta this year many acres needed water the last week of May. Some beans were 40-60 days old in late May and were in greater need of water than later planted beans.

When the initial irrigation is delayed, the result is stressed plants and ultimately plant death. If the soil is extremely dry, it will take longer to irrigate. This extended, saturated condition can kill plants. Following plant loss, the first reaction is to delay the second irrigation, and that is the wrong decision. Delaying irrigation stresses additional plants or once again stresses those that may be affected, but survived the first shock. Once the second irrigation has begun, additional plants may die but delaying irrigation will only add to the problem. The third scenario causing stress is where water cannot get off the low ends of the field. Getting water off a field is just as important as getting water on. I am a firm believer in turning on a little early versus late. Problems will be minimized when following this rule.

Although, only 30 percent of our soybean crop is irrigated, we need to rethink our approach to irrigation. A large percentage of our irrigated acreage is not watered timely. Many fields were watered only two maybe three times this year. Top yields may have required four to five furrow irrigations. Even in a year with above average rainfall, more than two furrow irrigations are needed on most fields.

Several have called regarding what they felt was a repeat of last year's seed rot conditions. Very little of this has been observed, but where early beans were allowed to stay in the field longer than they should some problems occurred. A lot of shriveled seed were observed on early plantings, but this condition is not phomopsis and occurs where the plant shuts down prematurely. In addition to shriveled seed, green seed are also a sign of the plant shutting down prematurely.

Phomopsis is a seed rot condition and, like aflatoxin, it is everywhere. Whether or not it expresses itself depends on conditions at and prior to harvest. A small amount of phomopsis was observed, but only in fields where beans were allowed to stay in the field unharvested for an extended period of time.

Several fields of early planted Group IV's retained leaves and the stems remained green. Pods were dry but this condition was deceiving in many instances. We observed problems in certain fields with some varieties, and I will attempt to discuss this in detail in the next agronomy notes.

 

Department of Plant and Soil Sciences
Box 9555
Mississippi State, MS 39762

Will McCarty, Ph.D.
Extension Leader

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