Agronomy Notes

July, 2002

Contents:

FORAGE AND PASTURES
RICE
COTTON
CORN
SOIL AND NUTRIENT MANAGEMENT
SOYBEAN

A Fair-Well From Dr. Malcolm Broome

This will be my last article in Agronomy Notes, as I have chosen to retire effective July 1, 2002. This last article revisits what I consider to be a vital management steps in continuing to grow quality forage, which is correctly managing Nitrogen and Potassium in our grasses. It has been my pleasure to share these monthly notes with you, and I hope in some way they were beneficial.

FORAGE AND PASTURES

Nitrogen, Potassium and Water Interaction in Grasses

Nitrogen and potassium are absorbed by plant roots when dissolved in the soil/water, thus their uptake is dependent on the moisture status of the soil. With adequate water, when nitrogen is absorbed, new plant proteins along with cell formation during the photosynthesis process create growth in grasses. Under inadequate nitrogen levels, grasses will absorb water that evaporates through the leaves, but new growth does not happen. Potassium is also critical to maintaining stands and producing quality forage. All our potassium fertilizers are water soluble and without water, uptake is lessened for plants. Both potassium and nitrogen rates should be adjusted to the yield potential as anticipated by rainfall amounts. On-going research at MSU suggests a 30 percent increase in yield of hybrid bermudagrass where one inch of water was applied weekly on a nitrogen rate of 68 pounds per acre compared to rainfall over a four week interval of time.

Nitrogen content of a grass is a direct measure of its protein content. The nitrogen that is extracted from a forage under laboratory analysis is multiplied by a factor of 6.25 and reported as percent crude protein. Nitrogen rates for grasses directly influence the crude protein level when harvested at the right stage of maturity. For example, a grass with two percent nitrogen contains 12.5 percent crude protein. If only three tons of hay are removed annually, it will contain approximately 150 pounds of nitrogen, 45 pounds of phosphorus, and 120 pounds of potassium. Other nutrients such as sulfur, calcium, zinc, etc. are also removed in much lower amounts.

Therefore, it is vitally important that hay fields be soil sampled on a regular schedule at least every one to no longer than three years. If nutrient levels are dropping, they need to be replaced as recommended by the soil lab report. A good rule of thumb for warm-season hay fields especially hybrid bermudagrass is to replace potassium at a rate of 30-40 pounds per ton of hay removed. This is best done in split applications to help prevent luxury consumption of potassium by the grass. A good plan would be apply potassium with first fertilizer in early spring, after the second hay harvest, and in the fall after the last hay harvest with the amount based on tons of hay removed since the last application. Taking a soil sample in the fall or winter will determine potassium needs for the next growing season. Potassium will also play a big part in stand persistence and cold hardiness. It is important that it be available in adequate amounts at all times, where nitrogen is only needed during the growth period of grasses.

Nitrogen will not be as effective without adequate water, but must be present for growth as well as protein. Proper fertility and adequate water is a two-way street without either part forage production will be lacking. However, we can control the fertility levels, and must do so before we can expect water to give that extra quantity and quality our animals need to give excellent performance. The best breeding program and health program will only go so far if the proper forage is not available for the animal to use.

RICE

Dr. Joe Street

Overall, the rice crop looks good and is progressing well. Actually, much of the rice is ahead of the DD50 predictions. The DD50 program compensated for the cold weather, but the rice apparently did not. Most of the early rice is well passed mid season and will be heading by mid July. As a reminder to those of you with later planted Cocodrie, it will reach mid-season in about 42 to 44 days from emergence and two-thirds of the fertilizer should be applied before mid-season. With our traditional late flooding, mid-season can occur before expected with Cocodrie. If at least two-thirds of the fertilizer is not applied prior to mid-season with Cocodrie or Priscilla, they have not reached maximum yields in research plots. For hybrid rice, the traditional mid-season application of fertilizer should be applied at late boot to five percent heading.

As this is written, the issue of applying Clincher within the buffer zone for peaches is being reviewed, discussed, and interpreted by all involved. Peaches are very sensitive to Clincher and drift should be avoided. Some aerial applicators have decided not to apply Clincher because of the restrictions. While the intent of the label was to prohibit the use of Clincher around commercial peaches, the label does not say commercial; thus, the Bureau of Plant Industry must interpret the label as written. Therefore, it is a violation of the federal label to apply Clincher by air within two miles of a peach tree if the wind is blowing away from the tree or four miles if the wind is blowing toward the peach tree. Clincher should not be applied if the wind speed is more than 10 miles per hour. We are looking into a special local needs label to address this issue. As of now, follow the label.

Sheath blight is beginning to occur in several areas, but I have not yet seen any blast. Some leaf blast has been reported on Wells in southern Arkansas and it has been observed on Bengal in Louisiana. Wells and the Clearfield varieties are the most blast susceptible varieties we grow, but they are planted on less than 10 percent of the acreage. Cocodrie and Priscilla are rated susceptible to blast, but we have not seen a problem with them in the field. We have not had a favorable blast year, but we should watch the weather and be ready to treat it if weather conditions occur which favor blast (cool/wet). Two new fungicides, Stratego and Gem, have received a federal label for use on rice this year. Try the new fungicides on a limited basis to become familiar with them. Stratego is a premix material and has activity on sheath blight and smut, but if it is applied early in the growing season for sheath blight, it may not last long enough for kernel smut control. Thus, timing will be critical. Gem may be used for sheath blight or blast control. With current rice prices, sheath blight pressure will have to be fairly heavy to justify treatment. Both Cocodrie and Priscilla are susceptible to kernel smut and treatment should be considered especially under high fertility situations. False smut is generally more prevalent on late planted rice.

I am seeing stinkbugs around fields already so it appears that this may be a heavy stinkbug year. Rice quality will be important again this year because of the high stocks of rice. Last year, those growers who applied a Karate initially had less peck damage than those who started with methyl. This year, Fury will also be available for stinkbug control.

COTTON

Dr. Will McCarty

The Mississippi cotton crop is in the widest array of growth stages for this time of year that I can remember. Planting lasted about eight weeks. May was about nine degrees below normal and had a tremendous effect on seedling development. June was warmer, but dry conditions persisted in much of the state. Entering July, our crop ranges from pre-square to near mid-bloom. Fruit retention has been good thus far, and major production problems have been limited.

The USDA / Mississippi agricultural Statistics Service crop report released June 28, 2002, estimated the Mississippi crop at 1,180,000 acres. I think that number is very realistic. Harvested acreage may be a little lower than that due to flooding or other problems. That indicates a reduction of 220,000 acres from the 1,400,000 acres predicted by the planting intention estimate released earlier this spring. Also, this indicates that Mississippi growers planted some 440,000 acres less than the 1,620,000 acres planted in 2001. Overall, USDA estimates that US cotton growers have planted a total acreage (all cotton) of 14,415,500 acres, down from the 15,768,500 acres planted in 2001. However, according to USDA, only 13,827,700 acres were harvested in 2001. By the way, the 1,180,000 planted acres in Mississippi places us third in acreage in the US in 2002. (#1 - Texas @ 5,820,000 acres and #2 - Georgia @ 1,500,000 acres)

Weed Control-When using hooded sprayers, be sure the spray stays under the hood. Some very effective chemicals can be applied with a hooded sprayer. However, if the hood is being used to apply a directed spray to the base of cotton plants, a material labeled for directed applications must be used. Watch tractor speed, tool bar height, hood bounce, and spray pressure. There have been questions about use of Gramoxone as a directed spray. Gramoxone is labeled for use under the hood, not as a directed spray. Do not apply Gramoxone as a directed spray to cotton.

Irrigation-Where irrigation can be used, implement cultural practices such as side dress fertilizer application and layby herbicides promptly to clear the way for timely irrigation. Be prepared to begin watering at or around first bloom if needed, and water as needed until open boll. Take all measures to ensure you are ready to start on time. Always consider soil moisture as you time irrigation. Looking at the soil can help prevent getting behind with limited output systems.

NAWF-The number of nodes above the first position white flower (NAWF) can be an informative measurement. To take this measurement, count the terminal as zero and count down the plant until you find the node with a first-position white bloom. When cotton begins to bloom, it should have from eight to nine nodes above this white bloom. If not, find out why; if it has more, find out why and then correct these problems. This measurement is a relatively good indicator of vegetative horse power in the plant and can be helpful in management. NAWF will generally be in the 8 to 9 range at first flower and will decrease as the bloom period progresses and boll load increases. As the plant reaches 5 NAWF it would be considered in cut-out.

If NAWF is greater than nine at first bloom it may be an indicator that vegetative growth may be out of control. If this condition exists find out why. In this investigation consider factors such as variety, square set, moisture, fertility and weather factors. If excessive vegetative growth looks like a potential problem, an application of a PGR may be in order.

Cotton should maintain a NAWF of about 7 through the first 2 weeks of bloom and then drive downward as it approaches cut-out. Changes in NAWF during this period may be related to weather or to changes in fruit retention. NAWF can be a good tool in PGR decisions.

Study Square Retention-Also, look at square retention on the first positions above the white bloom; this should be relatively high, in the range of 90 to 95 percent or more. At minimum, the square set above the WF should be above 80 percent. As the crop progresses, the white bloom will move up the plant and slowly catch up with the terminal until the crop reaches cut-out, which should occur when nodes above the white bloom reach about 4 to 5. As the bloom moves up the plant, keep up with boll retention on the first position of the branches below the white bloom.

Considerations in Using PIX-First of all, let me say when I mention PIX, I am referring to mepaquat chloride. It is available on the market in several products (PIX Plus-BASF, Mepex-Griffin, Mepachlor-Microflo, etc.).

Moisture supply and heat generally result in vigorous growing conditions early in the season. Plant height may easily exceed 30 inches at early bloom in some fields. Herbicide injury and drainage problems may impact this in many fields most years. Regardless, it is important to monitor and manage plant growth. Growers need adequate vegetative growth to support the soon-to-develop boll load, but if the plant is allowed to run away, it can impact management, especially fruit retention. History of vigorous early season growth and current crop condition may be the major factors in helping select the proper program or if PIX is needed at all. Several components of a crop monitoring program can help make PIX decisions. One of these is looking at plant vigor measured as inter node lengths (height:node ratio, HNR). Information still needs to be gathered to fine tune this system. HNR will vary but should be in the 1.5 to 1.8 range during mid- to late square. If the HNR exceeds 1.8, perhaps PIX is in order if growing conditions are good. If HNR is above 2.0 at first bloom, it is an indication the plant has tremendous vegetative horse power, and plant growth and fruit set must be closely monitored and managed.

Another measurement I have used is what I call Top-5 Length:Node Ratio (LNR-T5). I think this measurement, along with fruit set and Nodes Above White Flower (NAWF) can be helpful in plant management. Why so? Number one, because it is simple and can be measured quickly, thus increasing the likelihood it will be done. Second, the top five internodes represent the area of the plant where vegetative expansion is occurring. To take this measurement, count the uppermost unfurled main-stem leaf as 0 (zero) and count downward, 1-2-3-4-5. Measure and divide the length by five. The LNR-T5 is often similar to the HNR but is not affected by earlier growth. However, it is an accurate reflection of current growth. At early bloom, LNR-T5 should be in the 1.5-1.8 range. If greater than 1.8, the potential for rapid vegetative growth exist. Monitor NAWF and fruit set and make PIX decisions accordingly. As the NAWF progressively gets smaller, say six or five; the LNR-T5 should also be getting shorter if the plant has an average boll load of about 60 percent retention of first position sites. As fruit retention goes down, the plant will want to grow more vegetatively, and, therefore, the LNR-T5 will increase and the likelihood of a positive response to PIX will also increase. If first position boll retention is around 55 to 60 percent and the LNR-T5 is less than 1.5, take a long look at such things as previous PIX used, NAWF, soil moisture, etc., and then make a decision. These measurements are tools and can be a tremendous help when properly measured and applied.

Please monitor your fields. Of the measurements discussed, fruit retention and Nodes Above White Flower (NAWF) are the most powerful. If you keep track of development, you can make informed decisions regarding production practices.

Under conditions of good moisture and warm temperatures, cotton will want to produce vegetative growth. If you apply PIX, be sure you use a high enough rate to do the job. This year, fewer applications at higher rates may be better than many applications at low rates. As cotton grows bigger, it requires a higher rate, especially if the boll load drops.

All the measurements I have mentioned above are helpful and educational. However, the more I work with PIX, the more I gravitate to the "at-bloom" treatment followed by another application 10 to 14 days later with rate selection based on the variety, field condition and filed history. This method has been the most consistent method across the Cotton Belt. Of course, you should make all decisions on a field by-field basis and based on the needs of the cotton in the field. Note: The most consistent and highest probability of getting a positive yield to PIX has been on late planted cotton. I feel that a large portion of the 2002 crop may be candidates for PIX this year.

CORN

Dr. Erick Larson

Scout for Corn Borers - The peak flight of second generation corn borers is expected to be quite large this season and occur in late June and early July. Although pheromone traps are a good timing tool, do not solely rely on pheromone trap counts or your neighbor to determine an insect infestation - intensive scouting is normally necessary to quantify the infestation. Late-maturing corn generally suffers more yield loss from corn borer damage than early-maturing corn, because it is more attractive to corn borers (more succulent vegetation) and the damage occurs at earlier growth stages when plants are more susceptible to physiological stress. Heavily infested fields should be harvested as early as possible so that harvest losses (lodging and ear drop) are minimized.

Irrigation termination - One common irrigation error is terminating irrigation before physiological maturity (black layer) occurs. Mississippi corn planted during the suggested planting dates normally reaches physiological maturity beginning about the last week in July. Early irrigation termination will accelerate maturity, prohibiting kernels from reaching their full potential size and weight. Although kernels appear mature and corn water use is steadily declining at the dent stage, it is still too early to terminate irrigation. Potential kernel weight is only about 75% complete at the dent stage. Thus, termination of irrigation at the dent stage can reduce grain yields as much as 15-20%. Therefore, continue irrigating until physiological maturity occurs. Producers using center pivot irrigation systems can compensate for reduced demand by applying less water, rather than decreasing frequency. Producers using flood systems can only decrease irrigation frequency to compensate for lower water demand.

Kernel maturation: Corn kernels continue to accumulate seed weight until physiological maturity is reached. Physiological maturity normally occurs about 60 days after silking or 20 days after denting. Hard starch begins forming at the kernel tip when denting occurs. This hard starch layer gradually progresses to the kernel base over the next 20 days. This progression may be monitored observing the "milk-line" on kernels and is very important to irrigation scheduling. An abscission layer forms when the hard starch layer reaches the kernel base. Physiological maturity is signified by this black or brown abscission layer which is referred to as the "black layer". This abscission layer stops water and dry matter transfer into the kernel. Kernels will have a moisture content of 28-35% at this stage. The black layer may be found by shelling kernels from an ear and gently scraping away the seed coat to expose the abscission layer. The black layer formation occurs progressively from kernels at the tip of the ear to the base.

Check the milk-line: Corn producers can monitor kernel maturity be observing the progression of the milk-line. The milk-line is the borderline between the bright, clear yellow color of the hard seed coat outside the hard starch layer, compared to the milky, dull yellow color of the soft seed coat adjacent the dough layer. To observe the milk line, break a corn cob in half and observe the cross-section of the top half of the ear (which is the bottom side of the kernels - the side opposite the embryo). If the milk-line is half-way down the kernels, it will take about another 10 days to reach physiological maturity, since it takes about 20 days for the milk line to progress from the kernel tip to the base. Thus, the field needs supplemental irrigation water to supply moisture for 10 more days.

Sorghum black layer: Grain sorghum physiological maturity is characterized by formation of a black layer similar to corn. However, the abscission layer is visible without scraping the seed coat. The sorghum black layer can be found at the kernel base opposite the embryo. Kernels at the top of the head mature first, followed by kernels at the base of the head. Seed weight accumulation is complete and moisture typically ranges from 25-35% when physiological maturity occurs.

SOIL AND NUTRIENT MANAGEMENT

Dr. Larry Oldham

We need to realize and better appreciate the complexity of soils. It has been interesting over the past few years to work with people trying to make soils and soil fertility management conform to the rules of mathematics. However, soils have great variability in buffering capacity, or rather they differ in response to inputs of fertilizer or lime. In soils I like to say 1 plus 1 sometimes equals 2, sometimes it equals 1.1, sometimes it equals 4.

Topography, simply the lay of the land, plays a very important part in successful crop production. Often this is tied to overall climatic conditions: low spots perform well in dry years but high spots likely perform better in dry years.

There are several interrelated soil properties and practices connected to this observation. Soil water holding capacity depends on clay content and organic matter. Internal drainage depends on aggregation of the soil particles, organic matter content, tillage management, and other factors.

Despite this complexity, as the growing season progresses keep good notes on crop growth to aid future soil management decisions such as tillage systems or leveling. We likely never will have a magic equation for site specific management, but good management will always depend on careful observation of the system.

SOYBEAN

Dr. Alan Blaine

The recent rains were a blessing to many, but numerous areas received little if any moisture. The crop is quite varied (June 27) with plate fields filling pods to planting just taking place behind the MS floodwaters. The cold wet weather in May did not affect the state soybean crop to the degree it did cotton. Although many experienced (particularly south of Hwy. 8) slower growth, this was due mainly to lack of available moisture not cool conditions.

Normally, we do not see dry conditions this early in the season, but it has happened twice in the last five years. If you are utilizing the early planting system, you need to be prepared to address irrigation needs early. Most years, you can trigger this decision at first bloom, but this season was an exception. South of Hwy. 82, we had two fields in our verification program that needed supplemental water the last week of May. In these fields, plant growth was less than desired, but the soil profile had virtually no available moisture 18 inches deep. Spraying was not complete; therefore, irrigation was delayed a few days.

If you have fields that were planted early, but failed to grow off as you normally expected, the lack of moisture early was the likely cause. Avoid the urge to irrigate by the calendar; base irrigation on the crop's needs. Probing fields is essential to accurately determine moisture needs.

Allowing the crop to stress will alter maturity and translate into reduced yields. If you can irrigate, once you start, stay on schedule. Do not use visual crop stress as an indicator. Once stress is visible, a yield reduction has occurred.

Every year we get calls regarding beans turning yellow following irrigation. If this occurs one of two things has happened: 1) the crop was allowed to go too long without water, and the oxygen supply has become limited, or 2) it has taken on a surge of new growth following irrigation. Look at the canopy; if the yellowing is on the uppermost leaves/terminal, the plant is rapidly responding to water.

I personally like to start a little early, that way you do not get hurt as much by a rain event. When you delay irrigation, it takes a long time to water a field causing crop damage to be more severe. Base your needs to irrigate on the stage of the crop and available moisture to about 18 inches on heavy soils. Do not use the calendar.

I over heard Jim Thomas, Extension Ag Engineer, suggest to a grower that was concerned about irrigating in front of a potential rain, to water on 12 hour sets. Continue to water across the field and start over. This is not the problem, although many feel it is. You are usually not watering the entire field if a rain does occur. Watering early will avoid this problem, and I personal think this is the best approach. Earlier planting causes things to happen much sooner. Keep this in mind for the future.

Calls continue to come in about grasshoppers. Control thus far has been excellent. Check no-till fields carefully. We have treated ditches and turnrows in some areas to prevent an infestation later in the season. Keep in mind; we did not get in the grasshopper business over night. Without some measure of control or a cold, wet winter, we are not going to see them disappear over night.

Stink bugs are beginning to show up in early planted fields. We sprayed a field of Group IV's in mid-June that was planted in late-March. Stink bugs will primarily be found in Group IV's at this time. From bloom to mid-podfill, the threshold is one per three foot of row. As the crops get older, the threshold changes (mid-podfill through podfill). During the latter part of the season, the threshold is one per foot of row. The exception to this is seed beans where one per three foot of row should be used.

As corn, sorghum, and rice start to mature expect a migration of stink bugs into beans that are at a desirable stage of growth.

Time is fast approaching for decisions regarding late season management tools such as Dimilin, Quadris, Topsin M, and various insecticides. These are not whole farm decisions and every field is unique. Consider cropping history, bordering vegetation, irrigation, maturity group, and time of planting when making these decisions.

If you have questions regarding our findings as to what to use and when, do not hesitate to ask. We feel we have a good handle on the ins and outs of these late season options.

Weed control is rapidly coming to a close. The dry weather in some areas made many glad they had used a Roundup system considering the lack of pre-activity in some fields. Weed control has been average but post-activity of both conventional and Roundup Ready have experienced some lack of control. Weed emergence early was erratic in many fields and higher than normal rates of Roundup and tank mixes worked quite well. If you get behind the eight increasing, the Roundup rate above a pound can help you dig out of a mighty big hole. Depending on the material used cost will not be prohibitive.

Many of you will want to check with your Syngenta representative regarding a program they have for the use of Quadris and Karate Z as a tank mix on soybeans. You must leave untreated check for comparison and this program is for beans that have a history of 40 plus bushels per acre.

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

Will McCarty, Ph.D.
Extension Leader

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