Agronomy Notes

July, 2003

CONTENTS:

 

FORAGE AND PASTURE CROPS

Dr. David Lang

An Unusual Summer in Mississippi: Get Ready for Fall

We have hardly had much of a summer compared with most years with all the rain and "cool" weather so far in May and June. Although it has not been good for cotton, cool season forages have stayed actively growing into early July in the northern half of the state. Combined with the cool wet weather, the continued growth of cool season grasses has reduced the growth of summer grasses, particularly if ryegrass was over-seeded last fall. Being able to graze ryegrass or tall fescue into July has benefited animal performance since these cool season forages have better forage quality than warm season forages. A good practice is to graze or clip the late growth of cool season forages in order to allow the warm season forages to have adequate sunlight for growth. This keeps cool and warm season forage vegetative, particularly tall fescue, and improves forage quality. It's unusual to have tall fescue stay actively growing most summers in Mississippi, but if the temperature stays less than 90º F and we get adequate moisture, it will continue to grow. Ryegrass, since it's an annual, will die out once the seed heads mature. By the time you read this, the heat of summer may have finally arrived, and we will be looking for cool rains to break a mid-summer drought.

It will not be long before August is here and it will be time to plant winter annuals or tall fescue. Last fall there was a considerable problem with blast or gray leaf spot in ryegrass planted early prior to the tropical rains in late September and early October. Later ryegrass plantings were not as severely affected, so should you delay planting ryegrass this year? Probably not, but it might be wise to include oats or wheat in the seeding mixture as these small grains are not susceptible to blast. Add about a bushel (40 to 60 lbs.) of wheat or oat seed per acre to 20-30 lbs. of ryegrass seed. The oats will germinate quickly and provide early fall grazing, but may winterkill if the temperature drops into the teens. Wheat will not winterkill and it provides good mid-winter grazing even if ryegrass growth is slowed by a cold spell. Adding a small grain will provide an alternative winter forage if blast severely affects ryegrass again this fall. The occurrence of blast is directly related to tropical storms so if it's dry this fall we probably will not have a reoccurrence of blast.

Choosing a ryegrass variety can be complicated, but there are many good varieties sold by reputable seed companies, so you generally cannot go wrong if you select a variety that has been around for a while. See MAFES Information Bulletin 391: Mississippi Forage Crop Variety Trials 2002 for comparative data on many ryegrass (Display text cannot span more than one line) varieties tested in Mississippi. This publication also has data on other forage crop such as bermudagrass and tall fescue and will be updated in September.

As you plan for fall you should consider planting tall fescue if you are located in the northern half of the state. There are exciting, new varieties of tall fescue that contain a non-toxic endophyte marketed as MAXQ by Pennington Seed and ARKPlus marketed by FFF Cooperative. Research has shown that MAXQ persists in Mississippi similar to older lines of endophyte infected tall fescue. It's NOT like endophyte free tall fescue introduced in the 1980's that did not persist. Animal performance on MAXQ has been similar to ryegrass in terms of animal gains and milk production. It's also safe for horses, so check it out.

CORN

Dr. Erick Larson

Nitrogen loss - Wet, saturated conditions promoted substantial nitrogen loss in corn fields this year. Last month's article gave a formula for estimating denitrification loss from nitrogen fertilizer applied prior to the rainfall. However, mid-season field inspection is revealing more nitrogen loss than expected, especially on heavy clay soils. Nitrogen deficiency is characterized by yellowing (and later dying) beginning at the leaf tip and progressing along the leaf midrib on lower corn leaves. Growers can also submit leaf samples for nutrient analysis at many soil testing laboratories. Nitrogen deficiency symptoms are now readily apparent because many soils stayed saturated for two to three weeks, likely causing nitrogen loss ranging from 50 to 90%. Since high yielding corn requires large amounts of nitrogen, supplemental nitrogen application would likely be warranted, particularly on well drained soils. However, corn yield is most responsive supplemental nitrogen application a week or two prior to tasseling. Although the majority of this year's crop is well past tassel and will not likely respond to more nitrogen fertilizer, growers should strongly consider pre-tassel nitrogen application if wet weather persists in future seasons.

Scout for Corn Borers - The peak flight of second generation corn borers is expected to occur in 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

Dr. Erick Larson

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. Herbicide harvest aid application or irrigation termination should not occur before the black layer signifies physiological maturity.

SOYBEANS

Dr. Alan Blaine

The state soybean crop ranges from just planted to harvest in less than 30 days. The North Delta, North Mississippi and parts of South Mississippi were repeatedly plagued with above average rainfall through early July. Although the state crop as a whole is early these areas never got a break from the wet weather.

More replanting occurred this year than in previous years, but I feel some could have been avoided if we would have utilized the proper seed treatment. I realize as it gets later, it warms up and the tendency is to back off of seed treatments, but it is the free moisture (rainfall) that causes us to lose a stand ninety plus percent of the time. In every situation where we decide not to use a seed treatment, we are trying to out guess the weather.

I will discuss this problem in detail later, but at this time I want to highlight some late season management options you might what to consider.

In our SMART program the majority of our fields have reached a stage where we are intensively scouting for insects and mid/late season diseases. If planted with an early maturing variety we have some fields that are less than 40 days from being finished.

The fact that these fields are early allows us to avoid some late season insect and disease problems (primarily worms and foliar diseases). Mother Nature helped out in this regard so many of the concerns we have in full season soybeans we often avoid with the early system.

Several options exist but one centers around the use of foliar fungicides; mainly Quadris and Topsin M. Every field is not a candidate for fungicides, this decision should be based on variety, maturity group, planting date and cropping system (rotated and irrigated vs. dryland). Due to earliness, our response to a foliar fungicide on Group IV's has been very inconsistent. This changes as you plant later or use a full season variety.

Before you make any decision regarding late season strategies you must stage soybeans to accurately time applications. Most of these products recommend being applied between the R1 and R3 growth stage. To stage a plant, find the uppermost node with the most fully expanded leaves. This is node one, count down four nodes and determine the stage of growth at this point. R1 is when you observe the first bloom on the plant. R2 is when the plant is in full bloom. The R3 growth stage is when pods at this node are 3/16's of an inch long, and R5 is when the pods are fully elongated and just beginning seed development.

Do not let the indeterminate varieties fool you. Make your decision based on the fourth node down, do not consider fully elongated pods on the bottom of the plant. Group V's (being determinate) appear to easier to determine the stage of growth than indeterminate varieties but if you always consider the same node this determination becomes much easier.

A second option is the use of Dimilin. SMART fields in the Delta are earlier than the hills, but due to the yield potential we wanted some protection on this crop. You might be asking, Why Dimilin? Dimilin is probably the most underused/misunderstood product on the market. It has been found over the years to provide three benefits: 1) insect control, 2) disease control, and 3) yield enhancement (for reasons often not understood).

When we began making late season decisions on our Group IV's we only had 45 to 50 days until the crop was finished. Given this time frame we did not need long term protection. Based on our observations and past history we made the decision to put two ounces of Dimilin on all our SMART fields both irrigated and dryland.

I have two gentlemen working with me that made the observation in plots dating as far back as 1983, where they applied Dimilin, no frogeye leafspot was present. It can provide a number of benefits but it depends on your situation and cropping history. We are applying it between the R3-R4 growth stage, and it will provide about three weeks residual.

Another reason for putting it out at this stage is to get it into the plant before problems get started especially since it has a long residual. Last year we waited too long and did not stop the initial infection. Based on our work increasing, the rate above two ounces does not increase the residual. In the case of worms, Dimilin will provide excellent control of veletbean caterpillars, green cloverworms, cabbage loopers and salt marsh caterpillars (it only suppresses soybean loopers). In the South Delta under heavy looper pressure we have found that Dimilin will suppress loopers 7-14 days depending on the infestation level.

In addition, if Dimilin will provide at least one of the benefits observed in the past it will more than pay for itself. It is a fairly inexpensive option (2 oz. at approximately $2.60) compared to using Quadris or Topsin M. Since our response to Quadris and Topsin M has been less consistent on early planted soybeans, we feel this is the most cost effective option to utilize in early planted beans.

Is that application needed on every acre?, NO. Base it on the time of year, planting dates, variety and past cropping history. It is probably too late on early planted IV's (we sprayed our SMART fields between 6/20-7/9). One area of the state that will benefit greatly from the use of Dimilin is the hill area. Given the spectrum of worms, average planting dates, and particularly if you do not have someone checking your fields, growers in this region would be well served to blanket apply Dimilin at the R3 growth stage. Finally, consider this, if you will talk to your Uniroyal representative they have a guarantee program on this application, but it must be applied at the proper time.

Our final objective was to piggyback a pyrethroid or methyl with Dimilin (if needed) to clean up any early insect problems. Out of all the early planted fields we have in our program only three had stink bugs at a level that needed spraying prior to July 8th. There are treatable numbers out there, but they are quite erratic at this time. Fields needing spraying this early may be due to a past history, the field is serving as a trap crop, or you may be near over wintering areas.

In the case of early planting/early maturing varieties the plant avoids a lot of late season problems, not all but many. As our full season plantings (Group V's) approach R3-R4 we will be making additional decisions that will include Quadris. We feel that in order to achieve top yields it requires some additional late season management. We plan on applying Quadris plus Dimilin and a material for stink bugs if needed on all our irrigated Group V's. If insect pressure is not present we will not include an insecticide at that time. Fields will be monitored for pests and treated as necessary.

Traditionally south of Hwy. 82 (in the Delta) we have to spray for loopers every year. Since loopers are usually not as widespread North of Hwy. 82 a well timed Dimilin application may be all that is needed. However, do not fail to check soybean fields for late season insects. If loopers develop we have several excellent options available: Larvin, Tracer, etc. In addition we received a section 18 for Intrepid again this year for loopers.

We have an above average crop on the vast majority of the state's acreage so let's do what is necessary from a pest/disease stand point to reap the benefits.

RICE

Dr. Joe Street

Overall, the rice crop looks good and is progressing well. This is one of the most diverse crops that I have seen in a long time. Some rice is heading while some is still in the four-leaf stage. Actually, much of the rice is ahead of the DD50 predictions. The DD50 program compensated for the cool weather in May and June but the rice apparently did not. As a reminder to those of you with later planted Cocodrie, it will reach midseason in about 42 to 44 days from emergence and two-thirds of the fertilizer should be applied before midseason. With our traditional late flooding, midseason can occur before expected with Cocodrie. If at least two-thirds of the fertilizer is not applied prior to midseason with Cocodrie or Priscilla, they have not reached maximum yields in research plots. For hybrid rice, the traditional midseason application of fertilizer should be applied at late boot to five percent heading.

Herbicide drift continues to be a concern. The most critical time for drift of glyphosate or grass herbicides such as Select, Fusion, or Poast is from midseason to the boot stage.

Drift at midseason does not generally cause visual symptoms until heading and sometimes there are no visual symptoms. The only symptom may be reduced yield and/or reduced milling yield. Watch the wind when making applications near rice fields.

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 that 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 lately, but we should watch the weather and be ready to treat if weather conditions occur which favor blast (cool/wet). With current rice prices, sheath blight pressure will have to be fairly heavy to justify treatment. Cocodrie, Priscilla, and Francis 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 but there is no effective treatment.

Stinkbug infestations are scattered at this point but as more crops mature, I expect the stinkbug populations to increase. Rice quality will be important again this year because of the high stocks of rice. Last year, those growers who applied a residual insecticide like Karate or Mustang Max initially had less peck damage than those who started with methyl parathion. We have good yield potential this year so maintain the quality by controlling stinkbugs.

COTTON

Dr. Will McCarty

As was the case last year, the Mississippi cotton crop is in a wide array of growth stages for this time of year. Planting and replanting was spread over about eight to nine weeks. May and June brought above average rainfall and more than normal cloud cover. Fruit retention has been good thus far, and major insect problems have been limited.

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 your irrigation applications. 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 eight to nine range at first flower and will decrease as the bloom period progresses and boll load increases. As the plant reaches five 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 seven through the first two 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, and others, etc..). I will, for the purpose of this discussion include Pentia in this group. Pentia, from BASF, has a very similar mode of action and similar effect on cotton development as that of mepaquat chloride.

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" (a few days before bloom to 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 2003 crop could be, conditions dependant, candidates for PIX this year.

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

Will McCarty, Ph.D.
Extension Leader

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