Nationally soybean production totaled 3.14 billion bushels in 2004, the largest U.S. soybean crop in history. Nebraska ranked sixth in the nation in soybean production in 2004 with 220,875,000 bushels. (IANR photo by Brett Hampton)

April 22, 2005: Focus on Soybeans II

Research shows early planting of soybeans
crucial to optimizing soybean nodes and yield

The importance of node number was demonstrated in a two-year soybean trial funded by the Nebraska Soybean Board. The planting dates were early, mid, and late May and mid-June in 2003 (see Figure 1) and 2004 (similar results, so 2004 data not shown). The number of nodes on soybean main stems for each planting date was recorded twice a week.

Figure 1. The V-stage (node) number of plants growing in the four 2003 planting dates is plotted here on the vertical axis versus calendar date on the horizontal axis. The final number of nodes per stem in each planting date is shown at the Oct. 13 date. The linear equation for each planting date reflects the rate of node formation per day. Note that the values range from 0.26 to 0.27.

For each planting date, there was a lag between the day of planting and the V1 (unifoliolate leaf) stage that encompassed germination, seedling emergence (VE) and cotyledon (VC) stages. This lag was mainly a function of soil temperature (i.e., cool temperatures after planting extended this period; warm temperatures shortened it). However, on or after V1, all newly produced nodes appeared at a linear rate of about 0.26 node per day. This translates into one new node being produced every 3.85 days.

Note that the May 1 planted soybeans took longer to germinate and emerge than the May 15 planted soybeans (see Figure 1). Still, the May 1 planted seedlings started outputting a new node almost every four days well before the May 15 planted seedlings did. Also note that the node production trend lines for each planting date are parallel to each other. This means that late-planted soybean plants cannot produce nodes faster than the early planted soybean plants, and thus cannot “catch up” with the early-planted soybeans. All the soybeans in this research produced one new node every four days, no matter the planting date or cultivar. Results in 2004 were similar.

So what about the impact of planting date on seed yield, given that early planting generates more nodes? In 2003, each day planting was delayed after May 1 resulted in a 0.24 bu/ac yield loss, which translates into one bu/ac yield loss for every four days of planting delay. In 2004, each day of planting delay resulted in a 0.64 bu/ac yield loss. This means 2.6 bu/ac yield was lost with every four days of planting delay after May 1.

This research indicates that soybean producers need to plant early to optimize yield potential, but how early? Two factors should be considered:

Each year producers struggle with what fungicides they might put on their soybean seed prior to planting. Assessing the situation and potential need for a seed treatment is critical since this is the only time you get to make this decision. There are no curative applications for seedling diseases.

Soybeans growing in wheat relay cropping systems are at a greater risk of seedling disease due to the additional stress the shaded growing condition provides. Fusarium root rot can be a common problem in these fields at the seedling stage.

Therefore, especially given the wet conditions this week, I recommend a seed treatment fungicide if you have any of the following conditions:

• History of seedling/emergence problems. If you have a field with a history of stand problems, this year you will want to treat the seed with a good combination product.
• Early planting. If you’re considering early planting, fungicide seed treatments are a necessity. Cool, wet soils are conducive to poor stands without treatment. No-till fields will have cool soils later in the season than fields receiving some tillage. These will more commonly have seedling disease problems.
• Phytophthora. Fields with a history of Phytophthora will need additional metalaxyl or mefenoxam treatment. Even with resistant varieties I recommend a treatment since fields with Phytophthora generally also favor Pythium.

Soybean plants showing the effect of plant density on lowest pod height, plant height, and branching patterns. Left: 34,000 plants per acre; Right: 137,000 plants per acre.

Overall, research from across the Midwest still points to an optimum planting rate of 150,000 seed per acre. (Increase this rate to compensate for actual germination rates on the seed tag.) This rate equates to about nine seeds per linear foot of row in 30-inch rows. Given that soybean stands are reduced anywhere from 15% to 30% from planting through harvest, planting 150,000 seeds per acre should result in optimum harvest stands.

During a discussion of seeding rate at one of this year’s Cooperative Extension programs on 10 Ways to Save $20, a participant asked about the effect lower stands would have on pod heights. The standard answer is that reducing planting rates will lead to an increase in the number of low pods. Low pod heights can result in increased harvest losses since some combine heads are not able to pick up the lowest pods without bringing in significant amounts of soil or residue.

Factors affecting low pod height

We compiled Table 1 from research conducted in northern soybean production areas in the United States and Canada from the late 1970s through the early 1990s. (More recent information wasn’t available.) It shows how various management factors were found to affect lowest pod height and other plant characteristics.

Figure 1 (below) shows the effects of narrow rows and increased planting rate on low pod height. Average low pod height in this study for the indeterminate variety decreased as row space increased with 6.9-, 6.7-, and 6.1-inch pod height for the 10-, 20-, and 30-inch rows, respectively. This figure also shows the effect of increased plant populations on low pod height. As populations increased in 50,000 increments from 100,000 to 250,000 plants per acre, the pod heights increased from 6.0 to 7.0 inches. (The averages were: 6.0, 6.7, 6. 6 , and 7.0 inches for 100, 150, 200, and 250 thousand plants per acre, respectively.) The indeterminate variety in this study was Williams, a relatively tall, lanky variety. The shorter determinate variety in the study responded in the same way. Thus, the pod heights shown for Williams are most likely higher than we’d find in modern varieties, yet similar trends would still be expected today.

Figure 2 (below) shows the effect of delayed planting on plant height, lowest pod height, and node number. Plant heights and node numbers were closely related and were reduced as planting date was delayed. Lowest pod heights were also related to plant height and were reduced with delayed planting date. These again were taller indeterminate varieties than we grow now but a similar trend occurred with short determinates in the study and thus would be expected with modern varieties.

Should there still be concern about low pod heights? If planting rates are maintained at 150,000 or more seed per acre, pod heights are optimized (see Figure 1). If seeding rates are reduced, consider using a combination of some of the management factors listed in the Table 1. These may help to increase or at least stabilize low pod heights, resulting in fewer harvest losses.

New research on management options in relation to low pod height is important and needed.

Roger Elmore
Extension Crops Specialist
Lori Abendroth
Research and Extension Associate

Table 1. Effects of various management practices on lowest pod height and other plant characteristics. Management factor Effect on lowest pod heights Effect on other characteristics Cultivar Determinate varieties < Indeterminate varieties Plant heights: Determinate < Indeterminate varieties Cultivar Early varieties < Late varieties Harvest losses: Late varieties < Early varieties Wheat stubble height No effect on lowest pod height of soybeans (double crop situations) Row width Wide rows < Narrow rows (See Figure 1) Plant heights: Wide rows < Narrow rows Plant densities Low densities < High densities (See Figure 1) Plant heights, internode lengths: Low densities < High densities; Branch numbers, portion of yield in lower canopy: High densities < Low densities Planting date Late planting < Standard planting date (See Figure 2)

Figure 1. Effect of narrow rows and increased planting rate on low pod height. (R.O. Miller, 1981. Masters Thesis, University of Nebraska) Links to a larger version. Figure 2. Effect of delayed planting on plant height, lowest pod height, lowest pod height, and node number. (Beaver and Johnson. 1981. Agronomy Journal) Links to a larger version.

While soybean does not have as many options as corn, there are still quite a few products available. A pre-emergence herbicide makes sense in both Roundup Ready^® and conventional soybean systems because it eliminates most early weed competition and provides more opportunities for postemergence spray application.

Soybean rust update This week's Market Journal, Cooperative Extension's Television for Ag Business Decisions, focuses on soybean rust and the potential for problems in Nebraska. Tune in as host and Agricultural Economics Specialist Doug Jose visits with farm and ranch specialists about current topics in Nebraska agriculture. Loren Giesler, Extension plant pathologist, and Jim Specht, Department of Agronomy plant breeder, share the latest information on Asian soybean rust. (See the March 11 CropWatch for a special issue on soybean rust.) Also on this Market Journal program, Todd Sneller, administrator of the Nebraska Ethanol Board, will discuss Nebraska growing ethanol industry. (Visit their web site for a range of information, including: "Grand Opening of Nebraska's 7th E85 pump in Kearney will be Thursday, April 28. Come join us for E85 for 85 cents from 11 a.m. to 1 p.m." Visit the site for a map to the Pump & Pantry in Kearney. (Limit of 50 gallons of E85 for 85 cents per person.) Other guests this week will include: Mike Briggs, Seward cattle producer, discussing the beef markets; Katie Frey and Micky Wilson, UNL research students, on producing prawns, and Brain Fuchs, UNL Climate Data Specialist, on climate trends. Next week's Market Journal will feature a discussion of the Central American Free Trade Agreement. Market Journal is available on the Market Journal Web site for web viewing and on NET at 6:30 a.m. Saturdays and on NET2 at 9 a.m. on Sundays. For more sources and information, see marketjournal.unl.edu

Watch for such common winter annuals as field pennycress, shepherds purse, henbit, blue mustard and treacle mustard (bushy wallflower). They create the “green patches” often seen in the fall (October, November) and early spring (March-April). In addition, dandelion and curly dock, which are not winter annuals, can often be found when corn and soybean are being planted.

In no-till fields, winter annuals can be effectively controlled with herbicides. In corn and soybean they can be controlled 0-45 days before crop planting, depending on the herbicide, or after crop planting but before crop emergence. The same is true for fields planted with herbicide-tolerant crops (e.g. Roundup Ready or Liberty Link). Using pre-plant or pre-emergence herbicides with residual activity in Roundup Ready crops also provides a comfort zone in which to apply glyphosate products. Control winter annuals before they become too large for herbicides to efficiently control them.

Burndown herbicides that can be used in corn and grain sorghum and their per acre rates are: Aim (0.3 oz), 2-4-D Ester (1.0 pt); 2,4-D Ester + Banvel (0.5 pt + 0.5 pt); Banvel [atrazine (2 qt); atrazine + Banvel (2 qt + 0.5 pt), atrazine + 2,4-D (2.0 qt +1.0 pt); Field Master (4 qt), Gramoxone Extra (1.5 pt); Gramoxone Extra + atrazine (1.5 pt + 2.0 qt); Roundup Ultra Max (18-26 oz), Touchdown (24-32 oz) and one of many generic glyphosate products (24-32 oz). Pre-emergence herbicides for corn include: atrazine, Axiom, Balance, Bladex, and Prowl.

Examples of burndown herbicides in soybean that can be used 0-30 days before crop planting include: Aim (0.3 oz), Canopy (5-7 oz), Command 3E (1.5 pt); Gramoxone Extra (1.5 pt); Extreme (3 pts), Gauntlet (co-pack, 5.33 + 0.6 oz), Pursuit (4 oz), Pursuit Plus (2.5 pt), Sencor/Lexone DF (16/13 oz), Roundup Ultra Max (18-26 oz), Touchdown (24-32oz) and one of many generic glyphosates (24-32 oz). The list of pre-emergence herbicides in soybean includes: Axiom, Pursuit, Prowl, and Sencor/Lexone.

If spring temperatures are cool, glyphosate-based products used alone may not provide good control of winter annuals. Weeds need to be actively growing to move such systemic products throughout the plant. During a cold spring avoid using Roundup or other glyphosate-based products. Mixtures with atrazine, 2,4-D or other modes of action can improve weed control.

When buying glyphosate products, compare prices. UNL studies conducted over three years and six locations clearly showed that generic glyphosates provide control equal to the more costly products. Also, consult the label directions for additives and pre-plant and post-plant intervals. For example, corn should not be planted five days before or after application of 2,4-D. Also 2,4-D can be used for burndown in soybean but at least seven days prior to crop planting.

Stevan Knezevic
Extension Weeds Specialist
Northeast REC

Bean leaf beetle

Bean leaf beetles have two generations a year in Nebraska; however, since they overwinter as adults, three periods of beetle activity are seen in the growing season: Overwintering colonizers, F1 generation (offspring of the colonizers, the true first generation) and the F2 generation.

Bean leaf beetles overwinter as adults in leaf litter (woodlots) and soybean residue. They become active in April and May and often can be found in alfalfa prior to soybean emergence. As soybeans emerge, the beetles quickly move to the seedling plants, feeding on cotyledons and expanding leaf tissue. These overwintered beetles, called colonizers, mate and begin laying eggs. Females live about forty days and lay from 125 to 250 eggs. After egg laying is complete the colonizing population dwindles as the beetles die. A new generation of beetles (F1) will begin to emerge in late June to early July. The F1 beetles mate and produce a second generation of beetles (F2) that begin to emerge in mid to late August.

Bean leaf beetles vary in color, but are usually reddish to yellowish-tan. They are about 0.25 inch long and commonly have two black spots and a black border on the outside of each wing cover. These spots may be missing, but in all cases there is a small black triangle at the base of the wings near the thorax.

Because they move to soybean fields so soon after seedling emergence, early-planted fields will usually have more beetles and suffer the most injury. This has become more of a problem in recent years because planting dates seem to be getting earlier each year. Although the defoliation the beetles cause can appear quite severe, research in Nebraska and elsewhere has shown that it usually does not result in economic damage. Soybean plants can compensate for a large amount of early tissue loss, so it takes a considerable amount of beetle feeding to impact yield.

Table 1. VC Economic thresholds (beetles per plant) Crop value Pest management cost $/bu $/acre $6 $8 $10 $12 $5 3 4 4 6 $6 2 3 4 5 $7 2 3 3 5 $8 2 2 3 4 $9 2 2 3 3 $10 1 2 2 3 Table 2. V1 Economic thresholds (beetles per plant) Crop value Pest management cost $/bu $/acre $6 $8 $10 $12 $5 4 5 7 8 $6 3 4 6 7 $7 3 4 5 6 $8 3 3 4 5 $9 2 3 4 4 $10 2 3 3 4

Generally, unless insect populations are large enough to cause more than 50-60% defoliation of seedling soybeans, it is unlikely that treatment would be economically justified. The following table presents economic thresholds for bean leaf beetle on seedling soybean. Be aware that these thresholds are for defoliation of beans at VC - V1. If beetles enter the field right at or during seedling emergence, the thresholds will likely be lower because the beetles do not have leaf tissue to eat and will feed on the growing point, stem, and cotyledons. We do not have a good research base for bean leaf beetle injury to newly emerging soybean, but the thresholds are probably about 1 to 1.5 beetles lower than the VC thresholds.

Remember that early-planted soybeans are the most susceptible. If economic thresholds are reached, many insecticides are available for bean leaf beetle control. All will do an adequate job if applied according to label directions. If you plant early and regularly have economic levels of colonizing bean leaf beetles and/or bean pod mottle virus, insecticide seed treatments such as thiamethoxam may be warranted.

We are also finding that early season defoliation can affect weed management. In a collaborative project between the weed science and entomology programs at the Haskell Agricultural Laboratory Travis Gustafson, a UNL graduate student, found that seedling defoliation resulted in a need for earlier weed management. For example, with no defoliation, weeds could remain in the crop up to the V4 stage (third trifoliate) without significantly affecting yields. However, at 30% to 60% defoliation, weeds required removal by the V3 and V1 stages, respectively. This suggests that defoliation from bean leaf beetle feeding affects not only the final yield but also the timing of weed control.

Another reason some producers treat bean leaf beetle on seedling soybeans is to reduce the subsequent F1 and F2 generations; however, UNL Extension does not recommend this practice. There are many environmental factors that can impact beetle populations throughout the growing season, making it impractical to use spring beetle numbers to accurately predict if beetle populations will reach economically damaging levels in August.

Regular scouting and the use of the appropriate economic thresholds are the best way to manage late season bean leaf beetle in soybean. Late-season economic thresholds will be included in CropWatch later this summer.

Thomas Hunt
Extension Entomologist
Haskell Ag Lab
Keith Jarvi
IPM Extension Assistant
Both at the NEREC

Accumulated growing degree days (GDD), using a base of 48 degrees, can be used to help predict alfalfa weevil activity. Maximum damage will occur from about 450 to 600 GDDs. (Map developed by Al Dutcher, state meteorologist, High Plains Climate Center)

A graduate student in entomology, Abby Stilwell, is beginning research on a two-year study documenting the seasonal occurrence of alfalfa weevil larvae in eastern Nebraska. She will have additional field sites in northeast Nebraska.

The goal of her research is to have better defined degree-day predictions for alfalfa weevil management in eastern Nebraska. She is working with Drs. Tom Hunt and Bob Wright on her Master’s thesis research.

Bob Wright
Extension Entomologist

Soybean aphids on a leaf.

In much of the soybean aphid’s range, aphid infestation occurs during the vegetative stages and populations peak during the flowering stages. During the last three years in Nebraska, however, very few aphids have been found during the vegetative stages. It is usually mid-July before we begin to regularly find aphids. Although some fields in Nebraska reach economically damaging populations in late July, during 2003 and 2004 most aphid populations in Nebraska reached economically damaging populations in mid to late August. The question is, “Can these late populations cause significant yield loss?” Yes, data from 2004 indicates they can.

In 2004 a soybean aphid study was funded by the Nebraska Soybean Board as part of a North Central Soybean Research Program Project. In this study soybeans were infested with very low numbers of soybean aphids on July 23 and allowed to increase in population. Additional plots were kept aphid free for comparison.

The major aphid population growth occurred in just two weeks during the seed fill stage (R5), and population peaked about August 30, just prior to full pod (R6). The peak aphid population in infested plots ranged from 952 aphids per plant to 3,634 aphids per plant. Aphid-free plots averaged about 58 bu/ac while aphid infested plot yields ranged from about 47 to 55 bu/ac. The bottom line is: Aphid populations can increase very quickly and late season infestations can result in up to a 20% yield loss.

We will discuss this and other studies as the season progresses, but in the meantime following are the basics of soybean aphid management in Nebraska:

Soybean fields should be scouted once a week in late June to early July, increasing to twice a week as the season progresses. Remember, aphid numbers can change rapidly. The current recommended threshold for late vegetative through R5 stage soybeans is 250 aphids per plant (field average) with 80% of the plants infested and populations increasing. This gives you about a week to schedule treatment. Remember, determining if the aphid population is increasing requires several visits to the field.

Good insecticide coverage and penetration is critical for optimal control of soybean aphid, as aphids feed on the undersides of the leaves and within the canopy. Use sufficient water volume and pressure to reach well into the canopy.

Tips for successful sunflower planting

Proper planter preparation can pay big dividends with uniform emergence and better yields.

Choices are usually led by dealers/contractors, but many growers have found markets on their own. Once the type of sunflower and market potential are identified, the producer should make the following preparations.

Planter preparations

1. Be sure your planter is in top shape because uniform emergence is important for top quality and yield. Uniform emergence:
   • prevents later emerging plants from competing like a weed by using nutrients and eventually affecting yield (pounds and quality);
   • simplifies insect control because most plants are at the appropriate stage for control measures at the same time, limiting the need for additional spraying;
   • expedites harvest – no waiting on uneven ripening; and
   • improves seed quality (uniformity and seed size). This is more of a concern for confection sunflowers -- nonuniformity has less impact on oils. Oils for hulling, however, would warrant confection concerns.

Data provided by the National Sunflower Association shows the impact of seed treatments on yield.

1. Be aware of seed size impact:
   • Size two oils and the larger threes can be planted with corn plates or fingers
   • Size three and smaller will require special plates or fingers.
   • Medium and larger confections can also be planted with corn set ups.
2. Obtain a seed size that makes it easy to plant and fits your situation. While it is important to get all seed into moisture, remember that the larger seed requires more moisture for proper germination.
3. Seed treated with systemic insecticides have shown yield increases. Data presented by the National Sunflower Association from 11 plots in four states showed a 236-pound yield increase with systemic seed treatments. They control secondary insects and eliminate most planting concerns except cutworm.

1. Sunflower emerges best from a firm moist seed bed.
2. As a rule, you should have at least two or more feet of soil moisture profile for dryland situations. This reduces the risk of relying totally on rainfed precipitation.
3. Of course, a full moisture profile will increase the chance of crop success. If that would be the limited irrigation scenario (prewatering), it could do quite well. Yields over 3,000 lb have been obtained when the field started with a full profile and was rainfed after that.
4. Check for compacted soil layers or pans – these are the silent killers of high yields. Full development of the root mass is necessary to reach yield goals and support the plant.

Fertilizer preparations

1. Soil sampling should include data from a three-foot sample. The sunflower root system is deep and fibrous, allowing it to use nutrients other crops have left behind. Take credit for all residual nutrients.
2. The rule of thumb is 50 lbs nitrogen and 20 lbs phosphorus for each 1000 pounds of yield. This is what you should start with and take credit for nutrients in the soil test.
3. Yield goals for full irrigation could be 3000 lb or more. A circle of oils made over 4000 lb in the High Plains Growing area.
4. Yields with limited irrigation would be somewhat less, depending on rainfall. The rule of thumb is 7 inches of moisture to make seed and 150 pounds of yield per inch of moisture after that.

1. Research has shown that planting early -- in mid May in the primary sunflower regions of Nebraska -- produces higher yields that more than pay for the extra insect spraying that may be required. Plant when you can – immediately after corn and before beans is fine. Group 4 or 5 should be planted in May or the first days of June in the Panhandle. Planting earlier than mid May did not show any additional response.
2. Group 3 can be planted in mid May to mid June. Group 3 generally would be the best fit for the Panhandle.
3. Group 2 can be planted from mid May through June, if necessary. July plantings have done OK in special situations, but are more likely to face reduced yield from the shorter season or early freeze. Group 2 used for early harvest and planted in May have not shown the yield of Group 3 or Group 4.
4. Confection sunflower are usually Group 4 or Group 5 so plan ahead and plant prior to June 1.

Suggested planting populations can vary and may depend on personal experience and/or the wishes of the processor/contractor. Recommended seeding rates per acre for sunflower type are:

Oil: dryland, 17,000, and irrigated, 23,000

Confection: dryland, 14,000, and irrigated, 20,000.

1. Planting depth should be 1.5 to 2.5 inches, but should be at least 0.5 to 1 inch into moisture, then firmly packed and covered with 0.5 inch of dry soil for insulation.
2. Ripping can remove compacted layers and improve yields; however, without irrigation, plan on hotter, drier windier days as we proceed through the wide sunflower planting window into June and July. Consider the risk that ripping will further dry out the soil.
3. In good conditions plants should emerge in a week
4. Crusting rain will delay emergence about a week – treat like any other crop at this point.
5. Planting north to south is preferable to planting east to west to prevent plants from rubbing on each other and birds from standing on sunflower and eating on the head of another.

Seedling wheat in eastern Nebraska. (Photo by Brett Hampton)

Doug Anderson, Extension Educator in Nuckolls and Thayer counties: Pastures are slow this year which means annual and cool season grasses are feeling the effects of last year. Wheat is in good condition and has benefitted from recent moisture and now needs a little sun. Corn has been planted under pivots in both counties, but at the beginning of the week, I hadn’t seen any plants emerging yet.

Ron Seymour, Extension Educator in Adams County: Soil conditions are fairly wet, but most farmers are ready to plant corn when it dries some. Wheat is starting to joint and looks good. Alfalfa has greened up and is growing well.

Gary Zoubek, Extension Educator in York County: Many producers in the York area started corn planting early this week. Depending on the weather, we’ll see a lot get planted the next few days. The moisture we received last week was sure welcome!

USDA Nebraska Agricultural Statistics Service: Topsoil and subsoil moisture supplies continued above average and a year ago levels. As of Sunday, April 17, wheat conditions rated 1% very poor, 4% poor, 30% fair, 52% good, and 13% excellent. Fields were 19% jointed, ahead of last year at 14% and average of 9%.

Corn planting was underway with 5% planted compared to 6% last year and 4% average. Oats planted increased to 85%, ahead of last year at 81% and average of 67%. Thirty-three percent had emerged, ahead of 26% last year and average of 24%.

Sugar beet planting continued in the west with 21% completed, well behind last year at 52%. Alfalfa conditions rated 1% very poor, 4% poor, 22% fair, 54% good, and 19% excellent.

Note: A few are commercial-based sites. Any reference to commercial sites is made with the understanding that no discrimination is intended and no endorsement by Cooperative Extension is implied.