Agronomy Notes

June, 2001

Contents

CORN

Dr. Erick Larson

Irrigation needs - Corn's most critical and largest moisture requirement occurs during a four-week period following tasseling, which should occur during June and early July for most of Mississippi's crop. A water deficit during this period can reduce potential corn yields by up to 4 to 8 percent per day. Consequently, delaying irrigation can quickly reduce yield potential and evaporate profitability. Corn plants use up to 1.75 inches of water per week during peak water use, so producers must almost always supplement rainfall with irrigation to meet crop demand during this extremely critical period. Growers using irrigation should begin incrementally meeting crop demand before irrigation system capacity cannot replenish soil moisture, especially with center pivot irrigation systems.

Scouting Needs - Producers should continue scouting fields for potential problems and management information throughout the entire growing season. Producers with irrigation capacity should monitor soil moisture status nearly daily during the sensitive early reproductive period. Some likely insect pest problems to check include chinch bugs, sugarcane beetles and Southwestern corn borers. Numerous reports of chinch bug and sugar cane beetle damage occurred during the warm, dry conditions so prevalent during May. Historically, Southwestern corn borers have been another problem, particularly in the Delta and in some isolated north Mississippi counties; intensive, timely scouting is essential to diagnose, quantify and resolve the problem. Scouting should also reveal fertility deficiencies and prevalent weed competition problems. Weed problems can often be suppressed by applying various timely layby treatments. Although control options become more limited as corn becomes taller, scouting does provide insight into future problems. Understanding weed history and identifying current weed problems is important for future crops because corn weed problems can usually be addressed more effectively and economically with preemergence treatments than with postemergence treatments.

Grain Sorghum

Dr. Erick Larson

Irrigation timing - Grain sorghum is very drought-tolerant, but will respond positively to supplemental irrigation during droughty conditions. These characteristics make grain sorghum well suited for limited irrigation. Grain sorghum is most dependent upon moisture during the boot stage; boot stage is characterized by the head swelling inside the flag leaf sheath, immediately prior to heading. Grain sorghum water use is greatest during the rapid vegetative growth stages through the soft dough stage. Water use during this time typically peaks at about 1.5 inches per week. Water use rapidly declines after the soft dough stage. Therefore, a furrow-irrigation application just prior to the boot stage, followed by another at bloom (if needed) should provide nearly the same yield potential as full irrigation. Center-pivot irrigation systems typically require several applications since total water application is limited (compared to furrow irrigation) by runoff potential.

COTTON

Dr. Will McCarty

Roundup Ready Cotton - Apply Roundup Ultra, Touchdown or other glyphosate herbicides to Roundup Ready cotton according to all directions on the label. If applications are made in accordance with label instructions, no plant injury should occur. A major concern in making Roundup applications is drift onto non-Roundup Ready crops, or onto cotton that is past the size limits for over-the-top (OT) applications. Drifting Roundup onto Roundup Ready cotton that is past the labeled recommended size for OT applications may cause reduction in fruit set on lower branches. Use all precautions to ensure drift is minimized. If conditions will not allow safe OT applications, move on to directed applications. Again, when making directed spray applications of glyphosate materials to Roundup Ready cotton, it is essential that all directions and cautions on the label are read and followed. Using traditional materials such as fluometuron, prometryn, diuron, Cobra and/or MSMA can add to the effectiveness to a directed spray weed program and add residual control to the program. Directing with and laying by with residual herbicides is a sound weed control program in conventional and Roundup Ready cotton.

Hail Damage - Every year some fields are hit by hail, and deciding what to do with a field of cotton after a hail is often a difficult decision. When looking at a hail-damaged field, examine the plants to see what percentage of plants have a terminal, what percentage do not, and what percentage are cut off below the cotyledon node. Those cut off below the cotyledon node will probably not recover. Those that do not have a terminal will probably recover but produce a crazy plant with many branches. These plants can produce cotton but will mature late and be subjected to the problems associated with late cotton-i.e., insects, weather, and increased production cost with low potential returns. In other words, the risks are great.

Examine the stems of seedlings that survive. Stem damage may be severe enough to cause lodging later in the season. As the season progresses, additional considerations include the following: How "strong" is the soil? Where in the state is the field located, north or south? What is the variety in the field?

If the date is June 1 or later and the number of plants that are damaged to such a degree as to make survival unlikely is so great that the plant population will be below 20,000 plants per acre with numerous skips, destroying the stand may be in order. If the survivable plant population is greater than 20,000 plants per acre, and the stand is uniform, keep it. Plants with damaged terminals will produce vegetative branches that will set fruit. Maturity will be delayed, and management must be adjusted for a late crop.

If the weather turns favorable after a hail storm event, plant recovery will be phenomenal. One of the reasons for this is that the root:shoot ratio has changed tremendously. The plant should have the same size root system after the hail storm event as it did before the hail; however, the shoot, or leaf area, will be greatly reduced. The fact that the leaf area is reduced and injured is one of the reasons why attempting to foliar-feed hail-damaged cotton has not been successful. No miracle cures can be sprayed on the fields to increase survival or yields.

Side-dress Nitrogen - Watch the rate of side-dress nitrogen you apply; excessive rates of nitrogen will delay maturity while reducing yields and quality. Match nitrogen applications to nitrogen needs. Also, make your side-dress applications as soon as you can. There is no such thing as putting out side-dress nitrogen too early; avoid late applications.

Cotton requires about 50 to 60 pounds of supplemental nitrogen per bale of production on sandy loam to loam soils and about 60 to 70 pounds per bale on clay loams or heavier soils. If some of your cotton is on new cotton land, or has been in corn, rice, or soybeans for several years, or is just "strong" land, those rates may be reduced by 20 pounds and even 50 pounds in extreme cases. If you are planting cotton into a field where moisture is available and rapid, rank growth has been a problem, evaluate your nitrogen program carefully. Do not assume that you can put out any rate of nitrogen you want and control growth with mepaquat chloride (PIX Plus etc.). PIX Plus is a great material and a good management tool, but this is not the way to use PIX Plus or to grow cotton. There are several options as to how to use this product; these decisions must be made on a field-by-field basis. This product, or similar products, will not substitute for good management or make a poor crop into a good crop. Under good management, however, this product can improve plant efficiency and increase earliness. Proper use should be based on yield history, plant development, fruiting, and crop status. Plant monitoring goes hand in hand with mepaquat chlorate (PIX Plus, etc.) use. A key to successful use is to not let the crop become vegetative (with heavy fruit loss) before implementing a plant-growth-regulator program. Once the crop goes vegetative and fruit is shed, it is difficult to "bring back" into fruiting. For Mississippi, the best approach to successful use of PIX Plus generally involves an application at first bloom and a follow-up application in 14 days if needed. Rates should be based on individual field needs.

June is a critical month for cotton in Mississippi. Essentially, the squares set in June and early July will be the state's 2001 crop. Every precaution should be taken to prevent plant damage during this period. The weather is a factor that cannot be controlled, but growers must control all possible stress factors during square set. Keep in mind that it is extremely rare that a plant will physiologically abort a square before bloom.

RICE

Dr. Joe Street

The rice crop is progressing well and is ahead of average in many locations. Cocodrie will be the most widely planted variety this year followed by Priscilla, Lemont and Wells. Cocodrie will get to midseason (half-inch internode) earlier than the varieties that Mississippi rice producers have been growing. The average time from emergence to one-half inch internode is 44 days for Cocodrie, 50 days for Wells and 53 days for Priscilla and Lemont. To get a more accurate prediction based on weather for this year, use the DD50 program on the Internet (www.deltaweather.msstate.edu) or at your county agents office.

With the recent rains, it is tempting to hold the water and put fertilizer directly into the water. That will work but the best use of fertilizer is to apply it to dry soil and then flood. Many times this is difficult to do and it becomes necessary to apply the initial fertilizer into the flood. If the rice is young enough, split the fertilizer into three applications about 7 to 10 days apart. If there is not enough time for three applications before midseason, split the fertilizer into two applications and make the first application a little less than the second. Cocodrie and Priscilla yield better if two-thirds of the total fertilizer is applied prior to flood.

Growers continue to ask questions about the size of grass that Ricestar will control. Ricestar is not a big grass herbicide like Whip. Ricestar will consistently control three- to four-leaf barnyardgrass, but it is inconsistent for larger barnyardgrass. It will control one- to two-tillered sprangletop in most cases but may be inconsistent on that size grass also. The best thing is to follow the label for grass size for consistent control. No rice injury from Ricestar has been seen. Research is underway to increase grass activity by adding a small amount of Whip to Ricestar, especially for johnsongrass control, but the exact rates have not been identified. Tank mixing a broadleaf herbicide with Ricestar will (in many cases) cause antagonism. Aim and Basagran seem to be the least antagonistic. Permit would be a natural for nutsedge control, but antagonism has been a problem with this mixture.

For those of you who have not flooded and did not use Icon seed treatment, apply Karate or Dimilin within five to seven days after flood for water weevil control, especially if you have had water weevil infestations in the past. At this time, Fury has not received a label for water weevil control in rice.

SOYBEANS

Dr. Alan Blaine

With the exception of some acreage waiting on much needed moisture to complete planting and some double-cropped acreage, the Mississippi soybean crop is essentially planted. This crop was 80 percent planted by mid-May, a record for the state.

This crop has not been problem-free, but the vast majority of concerns have been associated with no-till.

The following points probably justify some attention now or on future crops.

  • There is no substitution for early burndowns. Regardless of whether you are going to plant no-till or not, early burndown will help eliminate unwanted vegetation, allowing you to better control time of plantings.
  • Earlier burndowns may help eliminate many of the insect problems that have been observed in no-till fields. Burning down early will remove a potential food source/home for many pests and may encourage their moving from planted fields before the crop emerges.
  • Continue to watch no-till fields for grasshoppers. Numbers are extremely high, but not present in all fields. Several materials are labeled, but Orthene has been the most widely and successfully used. Give any product you use sufficient time to work. Researchers are also evaluating preventive applications of low rates of Dimilin; results will be available once research is complete.
  • This crop was early, but many growers are still planting deep. If you are planting early, plant shallow. Rains prior to May 1are often big rains, and a tremendous detriment to soybean emergence.
  • Growers continue to report some minimal problems with the low rate of Apron. Researchers are investigating increasing the rate, but have no firm recommendations at this time.
  • Some fields will need to be replanted; two of the main reasons are deep planting or the failure to use seed treatment.
  • Several farmers have questions regarding plant populations. If plants are healthy, it is usually better to keep a 50 percent stand than replant. Soybeans have a tremendous capacity to compensate for thin stands and will do so. The down side is slower canopy closure, but using Roundup Ready soybeans and irrigation will help overcome this problem.

Weed control has been exceptional. However, two major concerns encountered have been lack of rainfall to incorporate pre-materials and the erratic emergence of weeds in many fields.

In the case of early plantings, many farmers were in an excellent situation concerning weed control. Weed emergence has been erratic. This is due to two reasons: cold conditions surrounding early planting, and dry weather. In many fields, early weed emergence was so erratic that although there were a few weeds getting large there were too few to justify spraying early. The dry weather helped out even more, because it kept that initial flush from occurring. Essentially, this meant free weed control. Whether because of using Roundup ready soybeans or because of the weather, weed control has been above average. If you sprayed early planted beans 7-14 days after emergence and had little emerged, you probably sprayed too soon.

In MSU's verification program, spraying was delayed until the fifth week after emergence.

In some fields where residual materials were added to the burndown, the fields have remained clean for an extended period of time. This was probably due to the lack of spring rains to keep these materials from breaking down; still, the combined effect was suppressed weed emergence.

The big question is, "Were there enough weeds to justify spraying?" As always, timing is much more important than the rate; you have to have something up in order to spray.

As an example, seven fields in the SMART program have had no application made entering the fifth week after emergence. Five of these fields had Goal applied in the burndown. One was land formed prior to planting and one following corn had Gramoxone put out behind the planter. When looking at these last week using the Herb computer program, researchers agreed that only one needed spraying. Four that did not need spraying had Goal applied previously. One was the land-planned field, and the other field behind corn will need spraying following a rain. Out of the seven fields, two will probably not receive any post herbicides at all. This is the result of a good residual burndown and early plantings. This points out field variability and the need to evaluate fields individually.

FORAGES AND PASTURES

Dr. Malcolm Broome

Nitrogen, Potassium and Water Interaction in Grasses - Nitrogen and potassium are absorbed by plant roots when dissolved in the soil/water, so 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 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. Ongoing 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 4-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 therefore directly influence the crude protein level when grasses are harvested at the right stage of maturity. For example, a grass with 2 percent nitrogen contains 12.5 percent crude protein and if only 3 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.

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 is to replace potassium at a rate of 30-40 pounds per ton of hay removed. Taking a soil sample in the fall or winter will determine potassium needs for the next growing season. Nitrogen will not be as effective without adequate water but must be present for growth as well as protein. Potassium will also play a big part in stand persistence and cold hardiness. It is important that potassium be available in adequate amounts at all times, where nitrogen is only needed during the growth period of grasses. Proper fertility and adequate water is a two-way street: without either part, forage production will be diminished.

WEED CONTROL

Dr. John Byrd

Pastures, pastures, and more pastures have been targeted for treating during May for weed control. Two sites have been treated for smutgrass. Oasis will be compared to Velpar and Dowpon M in areas that were burned this past spring, areas that will be burned this fall, and areas that will not be burned. Demonstrations conducted in 2000 on smutgrass treated before seedheads emerged with Oasis at 8, 10, or 12 oz/A provided better smutgrass control than those treated after seedheads emerged. However, plots treated with Velpar at 3 pints/A, regardless of application timing before or after seedhead emergence, provided the best smutgrass control. The photograph below shows the effect of these treatments on smutgrass one year after application.

This spring, researchers applied several treatments to prickly pear cactus to evaluate control. The best treatments appear to be Grazon P+D at 1 gallon per acre or Weedmaster applied at the same rate. Although the pads were not completely desiccated, there was no new growth. Gramoxone applied at 4 oz/gallon of water desiccated pads present at the time of application, but new pads were emerging. Grazon and Weedmaster applied at 1 or 2 quarts/A were not as effective as the higher rate. At 12 oz/A Oasis looked fair for prickly pear control, but completely killed the bahiagrass in the plot. At this evaluation timing, Arsenal, Velpar, Redeem, and Remedy were not effective for prickly pear control.

Several treatments have also been evaluated on bulrush, including Oasis, Arsenal, 2,4-D, Weedmaster, Grazon P+D, and Remedy. All products, except Oasis, were applied at only one rate, but were applied with nonionic surfactant, with 1 quart/A ammonium sulfate or 1% by volume with diesel fuel and 0.5% by volume nonionic surfactant. At three weeks after treatment, none of these treatments provided an acceptable level of bulrush control. Researchers will continue to evaluate these plots to determine if there is an acceptable treatment strategy for bulrush.

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

Will McCarty, Ph.D.
Extension Leader

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