University of Nebraska Institute of Agriculture and Natural Resources Cooperative Extension


Timely rains and a late freeze could aid Nebraska's soybean crop, which is lagging 200-500 growing degree units behind normal across most of the soybean production area and showing signs of moisture stress.
(Photo by Brett Hampton)

August 27, 2004

Plant Disease
Sudden Death Syndrome identified in Nebraska soybeans
Wheat Production
Seeding wheat on time pays yield rewards at harvest
Wahoo, Wesley, Jagalene leaders in 2004
Soybean Production
How glyphosate affects chlorophyll in glyphosate resistant soybean
Management
Crystal ball still hazy, but early frost lingers in the picture
Insect Control
Bean leaf beetle late season management
Soybean aphid numbers declining
Ag Programs/Resources/Updates
Ag briefs & Field updates
Specialists, Market Journal featured at Husker Harvest Days
West Central REC Centennial Sept. 17
Women in Ag Conference Sept. 16-17
Solution Days Sept. 1, 2 near Goehner
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(Above) The root systems of soybean plants with sudden death syndrome will have a deteriorated tap-root and lateral roots will only be evident in the upper soil profile. (Below) Foliar symptoms include interveinal necrosis and spots that coalesce to form brown streaks between the leaf veins with yellow margins. This is the first time this disease has been identified in Nebraska.
(Photos by Loren Giesler)

Sudden Death Syndrome identified in Nebraska soybeans

Last week at a field day near Nemaha a local soybean grower brought a plant with symptoms of Sudden Death Syndrome (SDS). After visiting the field and making more observations, SDS was confirmed. This is the first report of SDS in Nebraska; however, its arrival is not a surprise as Missouri and Iowa both have it.

Sudden Death Syndrome (SDS) of soybean is caused by the fungus Fusarium solani f. sp. glycines. This is a different fungus than the one that causes early season damping off problems associated with soybean stand. This year’s weather pattern, with both early season moisture and moisture at the early reproductive stages, is conducive to the development of SDS. Now is the time that you should see the full symptom expression of this disease.

SDS is favored by high yield environments. Soil compaction and high fertility levels have also been associated with increased levels of SDS. The foliar symptoms start with interveinal necrosis and the spots coalesce to form brown streaks between the leaf veins with yellow margins. Leaves eventually drop with the petiole (leaf stem) remaining attached. The root system will have a deteriorated tap-root and lateral roots will only be evident in the upper soil profile. The root cortex is light-gray to brown and may extend up the stem. Typically, plants can be easily pulled from the ground and a dark blue fungal growth will be visible on the roots. The blue color will not be evident in dry soil conditions.

At this time SDS does not appear to be a widespread problem in Nebraska and is most likely only going to be found in river bottom areas. It you have a field which is exhibiting symptoms of SDS, please contact us (402-472-8723; lgiesler1@unl.edu) so we can confirm it and get a better idea of how prevalent this disease is.

Loren J. Giesler
Extension Plant Pathologist


Soybean aphid numbers declining

As of August 24, most of the soybean aphid populations in Nebraska had stabilized or were decreasing, particularly in beans that were in the R5 stage or beyond. (R5 is when at least one pod in the uppermost four nodes of the plant has an 1/8 inch bean developing inside).

Lady beetles and other predators and parasites have caught up to the aphids in many fields. At this time, it appears that irrigated soybeans are safe from damage since the soybeans are maturing rapidly, have many predators, and have not shown signs of stress up to this point. The overall later maturity of the soybean crop appears to have lengthened the time the aphids have been present in the fields. Some later maturing dryland fields in northern counties may have some populations still increasing slightly, but now it is to the point where the return from a treatment is highly questionable. Almost a thousand or more aphids per plant would be necessary to provide a potential return on investment.

If you decide to treat, please leave an untreated check area to compare with the treated area for yield. From here on as the dryland beans mature and the irrigated beans remain greener, populations will begin to drop in the dryland and linger in the irrigated beans. Moisture stressed dryland areas will not have many aphids, as they will prefer more succulent plants.

Keith Jarvi
Extension Assistant
Integrated Pest Management
Northeast REC


Seeding wheat on time pays yield rewards at harvest

Table 1. Winter wheat seeding data and yield at North Platte.
Seeding date
Yield (bu/A)

September 2
2
September 15
27
September 25
42
Seeding date can have a major effect on winter wheat yields (Table 1). The recommended seeding dates for Nebraska’s winter wheat vary substantially from one end of the state to the other -- from Sept. 1 in the extreme northwest area to Oct. 1 in the southeast tip -- and have been proven and verified through years of research and farmer experience. Some years an earlier seeding may have an advantage and some years a later date may have an advantage, but in the long term, the suggested seeding dates will give the highest average yield.

The recommended seeding date represents a goal for seeding completion. As farm size and the number of acres increases for individual farmers, so does the length of time needed to complete seeding. The goal should be to have all the wheat planted by the ideal date. Plan your field order for planting accordingly; for example, plant higher elevation fields and those containing sandy soil first and leave lower fields and those with higher clay content until last.

Figure 1. Effect of seeding date on performance of seed and dual placement methods of phosphorus application at three locations and seeding dates.
If the seeding date is delayed or growing conditions prevent or delay root growth to the dual placement fertilizer band, seed fertilizer placement is the preferred application method (Figure 1). Poor root growth for whatever reason limits root-fertilizer contact and tillering, which affects yield. Much of the grain yield of winter wheat occurs on tillers that develop from buds in the axils of lower leaves. Under normal conditions, as much as 70% of the grain yield comes from tillers. Tillering also enables the plant to adapt to different conditions. Few tillers develop when moisture, nutrition, and other conditions are poor, whereas numerous tillers that increase the yield potential form when conditions are favorable.

Date of seeding greatly affects development of tillers in winter wheat. Seeding during the optimum period enables wheat to form sufficient but not excessive tillers. Early seeding results in too many fall tillers, which may compete with each other, become diseased, and deplete soil moisture so that grain yields are low. Late seeding gives plants little time to develop tillers, resulting in inadequate numbers of spikes (heads) for high yields the following spring.

Senescence and death might eliminate excessive tillers that form during the fall. Conversely, if too few tillers develop during fall, additional tillers may form during spring. However the yield potential may differ between tillers that develop during fall and those that develop during spring.

A study by Kansas State University to determine the seeding date effects on tiller development and productivity of winter wheat was conducted in a corn/soybean rotation at Hutchinson, Kansas. Two hard red winter wheat varieties, Jagger and 2137, were planted on four dates in the fall of 1995 (Table 2). The first date, September 28, was during the early part of the recommended period, September 26 to October 20. The second date, October 11, was one day after the Hessian fly-free date, and the last two dates, October 28 and November 11, were after the recommended period. Wheat varieties were planted at 60 lbs/A of seed in plots. Plots received 70 lbs N/A and 25 lbs P/A before planting and 50 lbs N/A in late February 1996.

Data for Jagger and 2137 were pooled, since results for the two varieties were similar. Nearly equal numbers of seedlings emerged after all planting dates except October 11, when considerably more plants occurred (Table 2). Plants from the first two dates tillered profusely, developing most of their tillers before they became dormant in late fall. Plants from the latter two seedings did not form any tillers before they became dormant, but those from the October 28 seeding developed a few tillers over winter. Only 46% and 65% of the fall tillers on plants from the first two dates, respectively, survived the winter, whereas 100% of the fall tillers on plants from the last two dates survived. About 50% to 60% of the surviving fall tillers from the first two dates formed spikes, while approximately 80% of the surviving tillers from the last two dates produced grain.

Plants from the first three seeding dates developed nearly 600 spring tillers/yd2, but plants from the last date formed only 213 spring tillers/yd2 (Table 2). About 30% of the spring tillers from the first two dates, 45% of the spring tillers from the third date, and 68% of the spring tillers from the fourth date produced grain. The total number of productive spikes ranged from 260 to 552/yd2 or 1.8 tillers per plant from the last seeding to 3.4 tillers per plant from the first seeding.

Table 2 also lists the yield from the four seeding dates. These dates need to be adjusted for the area in Nebraska to be seeded.

Figure 2. Recommended planting dates for Nebraska winter wheat.
Several factors were considered when developing the recommended seeding dates (Figure 2). In the Panhandle, the dates depend on elevation. Producers can determine the ideal date for each field by knowing the elevation. Using a starting point of September 15 for 3500 feet, add one day for each 100 feet lower and subtract one day for each 100 feet higher in elevation. For the rest of the state, September 25 or later seeding dates are recommended to avoid Hessian fly infestation.

Delayed planting dates also may be due to a need to avoid wheat streak mosaic virus, Russian Wheat Aphid, crown and root rot, and too much fall growth. Excessive fall growth causes excessive moisture use and stress. There are several other reasons for planting early. One is to get adequate ground cover to avoid erosion from wind and water. Another is to get adequate plant growth to assure winter hardiness. A third reason is to quicken maturity the following summer and avoid excessive heat stress.

The map is a guide rather than an absolute deadline. Each producer should make changes to ensure the planting dates fit the conditions of his or her farm.

Robert N. Klein
Extension Cropping Systems Specialist

Table 2. Mean date and number of plants that emerged; maximum, surviving, and productive fall tillers; maximum and productive spring tillers; and total productive spikes by Jagger and 2137 wheat varieties planted on four dates. (Kansas State University at Hutchinson, Kansas).
Date (1995)PlantsFall tillers (no/yd2)Spring tillers (no/yd2)Total spikesYield
PlantingEmergence(no/yd)MaxSurvivingProductiveMaxProductive(no/yd2)bu/A

Sept. 28Oct. 12141126657828158419547639.0
Oct. 11Oct. 1820791659436065919255257.7
Oct. 28Nov. 1514118318315260027242454.8
Nov. 13Nov. 30143147147117213144 26030.2
LSD 0.05)381361919214753106 4.9

Wahoo, Wesley, Jagalene ‘04 leaders

Wahoo and Jagalene were among the top performers in this year's University of Nebraska winter wheat variety trials, as they were last year. Under good conditions, Wesley also was a good performer. The results of this year's trials are now available in the extension publication, Fall Seed Guide 2004 (EC 04-103), available from county extension offices and on the Web at varietytest.unl.edu (Copies also were distributed widely in the most recent Midwest Messenger.)

Table 1. Three-year average yields (2002-2004) for the top three producers in University of Nebraska-Lincoln winter wheat variety trials, averaged together for all trial sites within a region. (Fall Seed Guide 2004, EC04-103) Visit the UNL Variety Test Web site for yields and results from this year's trials.
DistrictBrandVarietyYield

Southeast
NE9847167.5
213766.6
AGRIPROJagalene66.4
South Central
AGRIPROJagalene97.3
214591.5
Wesley89.3
West Central
AGRIPROJagalene59.6
Wahoo57.6
Wesley56.0
West, Dryland
Harry46.0
Jagalene45.5
Pronghorn45.2
West, Irrigated
Wesley102.2
Jagalene101.7
214596.8
Wahoo is a medium maturing, medium height variety similar to Arapahoe. It has shown good to very good winter hardiness and has a medium coleoptile length and moderate straw strength. It is moderately resistant to stem rust, leaf rust, and Hessian fly and is susceptible to wheat streak mosaic virus and barley yellow dwarf virus. This year's lowest yield for Wahoo was in Furnas County where the average yield in the trial plots was 7 bushels per acre. Cheyenne County reported the second lowest yield, 12 bushels per acre in a continuous dryland trial, as well as the top yield -- 89 bushels per acre in an irrigated trial.

Jagalene is a medium maturing variety with excellent straw strength. It is resistant to stem rust, leaf rust and soilborne wheat mosaic virus, moderately resistant to wheat streak mosaic virus and susceptible to Hessian fly. Jagalene is widely adapted and demonstrates good disease resistance and drought tolerance. Jagalene yields ranged from 11 bushels per acre in the Furnas County trial to 115 bushels per acre in the irrigated Cheyenne County trial.

Note: In both the Furnas and Cheyenne County continuous trials, seed was planted into dry soil and there was little moisture until early summer.

Trial conditions

As the results would indicate, conditions were less than favorable for top yields at several of the western Nebraska trial sites in the midst of a multi-year drought. Overall, wheat development was ahead of normal through the spring and early summer. However, just when we would have started harvesting the trials, a rainy period developed in eastern Nebraska, complicating harvest and lowering quality quite a bit. There was more sprouting than usual and lower test weights and protein. In most western Nebraska trials, yields were less than last year, but not bad . The rains there came a little later than normal, causing some of the late maturing varieties to look better than usual. Average production in the west central trials was 50 bushels per acre and in the Panhandle, 39 bushels per acre. Among the white wheats, performance was better in western Nebraska than in eastern Nebraska and production is not recommended for eastern counties.

When looking at any of the winter wheat variety trials, compare results from at least three years to get a more accurate perspective of how a particular variety might perform. This year's trials also included the first year of a three-year test of wheat blends. Depending on the blend and the site, generally the blends performed a couple bushels better per acre than the average of their individual components. The blend containing Millennium, Halt and Wahoo garnered as much as a six-bushel-per-acre increase in one location. By including Halt, the blend offered some resistance to Russian wheat aphid with less yield loss. The results from this year's blend trials is very preliminary.

Lenis Nelson
Extension Crop Variety and Seed Production Specialist


Ag briefs

Solution Days Sept. 1, 2 near Goehner

Solution Days 2004 will be offering practical solutions to everyday agronomic issues at field days this Wednesday and Thursday. The program will be offered twice -- Sept. 1 and 2 -- and help producers, farm managers and seed dealers learn how to work smarter, not harder, according to Keith Glewen, University of Nebraska Cooperative Extension educator.

Topics will include: solar radiation: timing and effects of radiation's changes on yields and disease, soybean yield response to soil moisture, new technologies, and drip and sprinkler irrigation technology.

Complimentary tickets are available from NK Brand Syngenta Seeds and the Nebraska Soybean Board. Participants are asked to bring their completed ticket panel to the field day to expedite registration. Solution Days will be held at the Syngenta Seeds Research farm near Goehner. From Interstate-80 take exit 373 and go 1/4 mile south.

For more information visit the Solution Days Web site.

Gary Zoubek, Extension Educator based in York County: We’ve received less than an inch of moisture the past month and the dry conditions have really begun to take a toll on dryland crops. The irrigators got a late start, but have been busier than normal. Now they can start focusing on scheduling their last irrigation (see cropwatch.unl.edu for a worksheet on this). Hopefully we’ll get some of the rain that the crops need so badly. Several fields have been treated for soybean aphid, but conditions vary greatly from field to field.

Duane Lienemann, Extension Educator based in Webster and Clay counties: The bulk of Webster County just can't seem to get a break with rains. We have had only about 0.30 inches in the last six weeks other than a few isolated spots, mostly in the southeast corner. Crops and pastures are really showing the effect at this time. We have dryland bean fields that will not make a crop this year. Pivot corners (especially overplanted acres) are really showing the effect of another drought. Dryland corn, especially that planted in wheat stubble, is looking pretty good at this time. Milo has headed but small heads are obvious. We had not seen much soybean aphid pressure until this last week. I would speculate that the cool weather we experienced the last three weeks brought them on. I have had reports and have seen fields with pretty impressive numbers, however the court is still out on whether it's beneficial to treat at this juncture. There is tremendous weed pressure in our pastures with common mullein, western ragweed and ironweed in the bottoms. I don't remember ever seeing so many weeds in our pastures -- especially the mullein. Jenny (Fleer) Rees and I had the opportunity to look at some pastures heavy with mullein and a couple of fields in southern Adams County that had an incredible amount of leaf miner damage plus some blight. Early planted irrigated corn is rapidly approaching black layer stage and most farmers are ceasing irrigation after one last watering this week. Replanted corn does not look like it will make a respectable crop this year -- we seem to be running out of heat unit days. Irrigated beans need more water and just didn't develop as we hoped this last three weeks. Dryland alfalfa fields will not have the tonnage hoped for this year. Third cutting will be light and we don't anticipate a fourth cutting.

Jennifer (Fleer) Rees, Extension Educator based in Clay and Webster counties: Several fields near Ayr showed blighted leaves up to the ear leaves. This condition existed in three different hybrids regardless of gravity or pivot irrigation. Heavy infestations of leaf miners up through ear leaves of plants throughout the fields caused the majority of damage. Symptoms were wavy, transparent streaks occurring from the outer margins in. Some gray leaf spot and common rust were also seen, primarily under pivot irrigation. Soybean aphids have been sprayed in Clay County for the past few weeks with a few fields still being sprayed this week at R5-R6. Duane Lienemann (Webster County extension) also found soybean aphids this week in Webster County.

Ralph Kulm, Extension Educator based in Holt and Boyd counties: Dryland crops are damaged beyond the help of rainfall. Much of the corn has either been cut for silage or baled. Many producers are grazing the small amount of third cutting alfalfa that has regrown as pastures are totally dried up and providing little in the way of nutrients. Irrigated crops continue to look very good. Corn is in the milk to dough stage and beans are well into the R5 stage. More of our recent warm weather will help ensure that the majority of our corn and beans will be safe from frost in 25 to 30 days.

Paul Hay, Extension educator based in Gage County: Much of the area is ending the season dry, which may reduce dryland corn yield potentials 2-3% Soybeans are also showing signs, but there is still hope if the area can get a general rain in the next week to 10 days. Cool nights have stalled out many milo fields and concern is mounting about whether the crop will be ready in time. We are certainly not ready for an early frost.

Karen L DeBoer, Extension Educator based in Cheyenne County: Soil conditions are dry and crops need warm weather to continue growing. The crops just aren’t maturing as fast as they should be.

Delroy Hemsath, Extension Educator based in Dakota, Dixon, and Thurston counties: Soybeans are in the R5 stage in general. Dryness, warm temperatures and windy conditions have caused stress in the last week. Soybean aphids have most likely reached their peak and are on the downswing in numbers. Most corn is in the dough stage and there are no serious stress problems except on the sandy soils. Yield potential in dryland corn still looks good. Potential for spider mites is set with the windy conditions and dryness. Alfalfa third cutting is being harvested and the quality should be good. Pastures are brown from lack of moisture and the grass has been grazed down.

Farm Mediation: The Nebraska Department of Agriculture Farm Mediation Program conducts clinics on farm finances; the laws, regulations and policies governing FSA; debt restructuring and other legal options; and related topics. Contact the Farm Hotline (800-464-0258) for more information.


Crystal ball still hazy but early frost lingers in the picture

As we enter the last full week of August, concerns are being raised about an early freeze potential and crop moisture shortfalls. Temperatures across northern Montana and North Dakota fell below 32oF during the last week. In addition, cooler than normal temperatures across the central Plains during the last 45 days has helped mask precipitation shortfalls and subsequent crop stress problems. As of Sunday (August 22), Nebraska Agricultural Statistics Service indicated that 54% of the state’s topsoil is short to very short of moisture, while 70% of the subsoil falls into this category. There have been periodic heavy rains across eastern Nebraska during the last 30 days, but they haven’t been widespread.

As we entered the 2004 summer crop season, corn and soybean emergence were a full 10-14 days ahead of the five-year average. By August 15, these two crops had fallen behind the five-year average and last year’s ratings. During the last 60 days average temperatures have been 3-5oF below normal and the early emergence advantage has been eliminated.

Growing Degree Day (GDD) base 50oF accumulations since April 15 are running an average of 12-15% behind normal. The Panhandle and Sandhills region have accumulated 1800-1950 units (location dependent) since April 15 and are 200-300 units behind normal. GDD accumulations since April 15 for the rest of the state are: northeast (1950-2050), southwest and central (1950-2150), south central (2000-2250), east central and southeast (2150-2400).

Many locations in the western third of the state were forced to replant corn due to the May freeze. In these replanted areas, accumulations are 200-400 units behind the April 15-to-date totals. Based on average corn emergence dates, GDDs are 100-150 units less than the April 15 totals.

In terms of crop progress, the Nebraska Agricultural Statistics Service reported that 83% of the state’s corn had reached the dough stage, compared to a five-year average of 86%. Approximately 31% of the corn had reached the dent stage compared to 53% for the five-year average. None of the crop had been reported as mature, compared to the five-year average of 4%. Only 4% of the soybeans were turning color, compared to the five-year average of 10%.

Crop condition ratings for corn and soybeans for this point in the season continued to exceed last year’s ratings. Irrigated corn was rated 83% good to excellent compared to 71% last year. Dryland corn was rated at 71% good to excellent, compared to 14% last year. Soybeans were rated 67% good to excellent, while sorghum was rated at 62%.

Moisture stress has been reported in some corn and soybean fields in eastern Nebraska. Scattered heavy rainfall this week in eastern and north central Nebraska should help alleviate short-term moisture concerns for pod filling soybeans. Corn tippage was being reported, while soybean reports indicated moderate to severe wilting and premature leaf drop in moisture-starved fields.

Weather models have been inconsistent the entire summer concerning the strength and timing of cold air intrusions across the central United States. What does appear to be consistent is that cold air days are beating out warm air days by a two to one ratio. When below normal temperatures move into the Plains, they hold on for 5-10 days, followed by two to five days of above normal conditions.

During three days of weather model runs (August 22-24), three different forecasts appeared for the next two weeks. A significant trough was expected to move through the central United States from the Pacific Northwest by the end of this week. This will usher in below normal temperatures and drier weather through early next week. It is at this point where the models diverge on their solutions.

The first solution indicates a quick warm-up followed by another strong cool down. The second indicates a sustained period of above normal temperatures, while the third indicates normal temperature conditions. Based on the persistent 45-day pattern, the first solution appears to be safest, but also the one that carries the greatest likelihood for an early freeze.

If the first forecast solution verifies, anticipate that temperatures will take a nose dive by the first weekend of September, then moderate through the middle of the following week. Another shot of cold air should be expected September 10-15. Freezing temperatures for this model solution are indicated to reach southwestern and south central Canada by September 8. If the models are correct, freezing temperatures will occur across North Dakota, Montana, and northern South Dakota September 9-11.

For Nebraska, there is a greater risk of an earlier than normal freeze this year based on the current weather pattern. The most likely scenario would be for the event to occur September 20-28. This would be one to two weeks ahead of normal; however, we can’t rule out that the cold air expected to drop into the Northern Plains September 9-11 may result in freezing temperatures across the Panhandle and Sandhills region.

Al Dutcher
Extension State Climatologist


Visit with Extension specialists and Market Journal panelists at Husker Harvest Days

University of Nebraska extension specialists will be available to answer questions in a variety of agricultural, rural, family living and natural resource areas throughout the 27th Annual Husker Harvest Days show Sept. 14-16 in Grand Island. UNL’s Institute of Agriculture and Natural Resources (IANR) will have more than 20 exhibits and displays at its Husker Red metal building at lot 325 on East Third St. of the show grounds. Many of the Extension specialists who regularly contribute to CropWatch will be available throughout Husker Harvest Days to answer questions.

“NU Cooperative Extension offers a one-stop service center for information and answers to questions on many of the most timely and pertinent rural, agricultural, family and environmental topics,” said Larry Schulze, NU pesticide education specialist and coordinator of the IANR displays.

Displays and speakers will focus on current topics, including: soybean aphids and soybean rust, technology in crop production, cost share funding for livestock producers, water quality research and water conservation, identification of blue-green algae in lakes and ponds, 4-H, integrated crop management, pesticide security and new pesticide labeling, the Nebraska LEAD program, cooking for food safety, corn husk fiber for fabrics, Nebraska families weathering life’s ups and downs, and more. Sawmill demonstrations will be part of an exhibit on Nebraska’s lumber industry, Schulze added.

Individuals wanting to explore opportunities in higher education can visit with representatives of the College of Agricultural Sciences and Natural Resources, School of Natural Resources, College of Technical Agriculture at Curtis and Department of Agronomy and Horticulture, Schulze said.

Market Journal

Cooperative Extension’s Market Journal program will again be broadcasting two live shows a day from Husker Harvest Days. Attendees are invited to take a break in the shade of the presentation tent and listen to speakers address current issues of agriculture and new ag products at Nebraska’s largest agricultural trade show.

The presentation tent will be located near the Big Red IANR Building. For more information visit the Market Journal Web site.

Tuesday

11 a.m. What’s New at Husker Harvest Days?
2 p.m. What About Precision Agriculture
Wednesday
11 a.m. New Cropping Systems
2 p.m. Water Issues and Nebraska’s Agriculture
Thursday
11 a.m. New Seeds and What They Do
2 p.m. Market Journal Programming at Husker Harvest Days

Governor’s news conference

IANR again will host Governor Mike Johanns and State Director of Agriculture Merlyn Carlson in a news conference at 10 a.m. Tuesday, Sept. 14.

“NU and IANR have been part of Husker Harvest Days from the very beginning in 1978 and we again welcome the opportunity to be available to the public during this premier agricultural event,” Schulze said.

Steven W. Ress
Communications Specialist


Study examines how glyphosate affects chlorophyll in glyphosate resistant soybean

This is the second CropWatch article addressing the impact of glyphosate herbicide on glyphosate resistant soybeans. The first article, “Glyphosate use and soybean nodulation – is there a link?”, was in the July 30 CropWatch.

Figure 1. Chlorophyll content in tested soybean leaves in 2003, graphed as a percentage of the control treatment (no glyphosate). The 1X glyphosate rate was applied to the soybeans early in the season at 7 (V1) and 21 (V4) DAE. The 1.5X glyphosate rate was applied to the soybeans at 21 (V4) and 42 (V9) DAE. Measurements of leaf chlorophyll were collected approximately 10 days after the applications.
This article reports on research to study how glyphosate influences the amount of chlorophyll in soybean leaves. Chlorophyll content can be thought of as the “greenness” of the leaf. This “greenness” is used as a reference for the nitrogen contained within the plant. A plant experiencing nitrogen stress will become yellowed and this is seen as a reduction in chlorophyll.

Once atmospheric nitrogen is converted by Bradyrhizobia japonicum (nitrogen-fixing bacteria) to nitrogen compounds useable by the plant; they are transported to the above-ground portion of the soybean. When glyphosate is applied to the soybean it is moved downward and can possibly interfere with this nitrogen-fixing process. If an inhibition does occur within the nodules, we would expect to see less nitrogen moved above to the leaves. Nitrogen moves in a cyclical pattern within the plant, and nodules will respond to nitrogen stress by converting more nitrogen to meet the demands of the growing plant. Once the plant has enough nitrogen, the bacteria conversion process will slow down. Thus, we can see that nitrogen fixation is a unique process in which the soybean plant and bacteria work closely together throughout the season.

The treatments we applied are the same as those listed in the previous article and as such will not be repeated here, except to note that glyphosate was applied at three soybean growth stages (V1, V4, and V9). (See Figure 1 for more information on specific glyphosate applications.) Overall, chlorophyll content was reduced 2-12% at each growth stage following a glyphosate application. Sample data that is representative of this response is shown in Figure 1. The chlorophyll content was measured with an instrument called a SPAD meter which is sensitive to slight chlorophyll differences. Without the use of this instrument we would not have been able to see any difference between glyphosate treated and untreated soybeans. The chlorophyll response was more variable early in the season, following the V1 and V4 applications. After these early applications, the chlorophyll content was typically reduced but in a few instances it was unaffected. The late season application (V9) consistently caused a reduction. These reductions in chlorophyll content appeared to be due to two factors:

Figure 2. Percentage of protein (top) and oil in soybean seed in 2002. (Click on image for larger version.)
Chlorophyll content within leaf tissue was reduced following nearly every glyphosate treatment. The timing of application appears more important in the reduction of chlorophyll than the actual rate of glyphosate.

We also looked at the long-term effect of these chlorophyll fluctuations within the plant by measuring the protein and oil content in the soybean seed. Protein and oil content will vary across environments, years, and varieties, yet nitrogen is important in determining the amount of protein within the seed. Interestingly, seed protein content was increased in two of our locations after the late season glyphosate treatments (Figure 2). We are conducting more research to determine if this is due solely to the glyphosate or to the combination of glyphosate and ammonium sulfate.

Our research identifies glyphosate as possibly causing fluctuations in the plant’s nitrogen status. This is based on the fact that chlorophyll content was reduced after nearly every glyphosate application, which probably created periods of decreased nitrogen levels. Through this research, we can see that although glyphosate resistant soybean is able to tolerate glyphosate it is incorrect to think that the plant is completely unaffected by this herbicide.

Reference: Parsons et al., 1993

Lori Abendroth
Research and Extension Associate, Department of Agronomy and Horticulture

Roger Elmore
Extension Crop Specialist

Fred Roeth
Extension Weed Specialist


Bean leaf beetle -- late season management

As soybean aphid frenzy subsides, growers should be on the alert for another soybean insect pest which must be managed for the remainder of the season. We’ve had one generation of bean leaf beetles and are now experiencing renewed feeding as the true second generation of beetles emerges and feeds on leaves and developing pods. Following is a review of the beetle’s biology and suggestions for managing it.

Table 1. Economic thresholds in beetles per row foot for R5-R6 (beginning pod and full seed) soybeans in 30-inch rows.

Soybean valuePest management costs per acre

  $7.00$8.00$9.00$10.00$11.00$12.00
$4.507.1 8.19.110.111.112.1
$5.006.47.38.29.1 10.010.9
$5.505.86.67.48.39.1 9.9
$6.005.36.16.87.68.3 9.1

 

Table 2. Economic thresholds in beetles per row foot for R5-R6 (beginning pod and full seed) soybeans in 7 inch rows.

Soybean valuePest management costs per acre

  $7.00 $8.00 $9.00 $10.00 $11.00 $12.00
$4.50 1.71.92.12.42.62.8
$5.001.51.71.92.12.3 2.5
$5.501.41.51.71.92.12.3
$6.001.21.41.61.81.92.1

 

Table 3. Economic thresholds in beetles per sweep for bean leaf beetles on stage R6 soybeans in 30-inch rows. Numbers in parenthesis are for beans drilled in 7-inch rows. (R6 is defined as a green seed filling the pod cavity in one of the four uppermost nodes with a fully developed leaf (seeds touching.)

Soybean valuePest management costs per acre

  $6.00 $8.00 $10.00 $12.00
$5.004 (3)5 (4)6 (5)8 (5)
$6.003 (2)4 (3)5 (4)6 (5)
$7.003 (2)4 (3)4 (3)5 (4)

Beetle biology

Two generations of bean leaf beetles develop each year in Nebraska. The second generation overwinter as adults and are the ones seen early in the year feeding on seedling soybeans. These beetles feed, mate, lay eggs and die in early-mid June. Usually there is a distinct period from mid June to early July when few if any beetles are present in the field, before the first generation emerges. Total developmental time from egg to adult can range from 25 to 40 days. Because of this range of development, it is common to see adults from the first generation and the second generation in the field at the same time. In other words, the generations overlap and beetles will be present at some level from mid-July until the end of the growing season. Because of this overlap, it is important to regularly monitor beetles to determine population shifts. This information can then be used to make more informed management decisions.

Bean leaf beetles will feed on soybean leaves throughout the season, but leaf feeding seldom causes yield loss. Most damage (economic yield loss) occurs when beetles feed on developing pods. This yield loss can occur in several ways. Pods may be clipped from the plants, but this is not the primary cause of yield loss. Many flowers and pods are aborted naturally and to blame pod loss on bean leaf beetle feeding may be a costly mistake. Beetles normally injure soybean pods by feeding on the outside layer, leaving a thin layer of tissue still covering the seed. Usually, except with very small pods, they won’t eat into the developing seed. Fungal pathogens may enter the pod from the feeding sites, causing seeds to appear shrunken, discolored, and moldy, which can result in dockage. After full pods are formed and seeds begin developing, soybeans are most susceptible to yield loss from pod feeding.

The best time to sample is before significant pod feeding occurs, but after second generation beetles have emerged. Second generation bean leaf beetles are emerging and beetle numbers will be approaching their highest levels for the summer. Beetle numbers will slowly decline as beans mature and beetles move to overwintering sites.

Economic thresholds have been developed for both drop cloth (beetles per foot of row) or sweep net (beetles per sweep) sampling (Tables 1-3). Perhaps the most accurate way to sample beetles is with a drop (or shake) cloth. A drop cloth is a 3 x 3 ft piece of muslin or plastic attached on each side to dowel rods. Hold one rod against the base of the plant and lay the cloth between the rows. Shake the plants against the cloth to knock off the insects, and count the beetles. Remember to estimate the number per row foot, so if you use a three-foot cloth divide your total by three. Sample several areas of the field to get a more accurate estimate. In narrow row beans you can still sample with a drop cloth, but the procedure is slightly different. Set the rod at the base of the row of plants and lay part of the cloth on the ground and hold the rest of the cloth upright or over the opposite row to be sampled. Shake the soybeans against the upright cloth, and then count the beetles knocked down on the bottom of the cloth.

Thresholds are based on the number of beetles per foot of row, which varies according to total application cost and the crop value per bushel.

Tables 1-3 show economic thresholds for beans in 30- and 7-inch rows. To use the tables find the number that fits both crop value and application costs. For example, if you set the value of your soybeans at $6 per bushel and your application costs would be $9, you would need 6.8 or more beetles per foot of row to justify an application in 30-inch row beans or 1.6 or more beetles per foot of row in 7-inch row beans.

Sweep at least five randomly selected sites. Walk through the field at an even pace, performing about 25 sweeping arcs. The best sweeping action for bean leaf beetle is a consistent upward motion through the foliage, using as much force as needed to move the net smoothly through the foliage. Bean leaf beetle activity varies during the day. Activity patterns suggest the best times to sample are around mid-morning or in the afternoon. Try to maintain a similar sampling time in each field to eliminate variability.

Economic thresholds for reproductive stage soybeans other than R6 are probably higher (more beetles are needed to justify a treatment). This is because pods on plants past R6 are maturing and there is less green pod tissue available for beetle feeding, and plants in earlier reproductive stages have greater yield compensation potential than those in R6 or older.

Keith Jarvi
Integrated Pest Management Assistant

Northeast REC
Tom Hunt
Extension Entomology Specialist
Haskell Ag Lab, Northeast REC

Table 4. Insecticides registered for bean leaf beetles. Bean leaf beetles can be controlled by several insecticides. Be aware that most have 14-day or more pre harvest intervals (phi). Here is a table of insecticides for bean leaf beetle control.
Restricted UseProduct NameRatePre-harvest interval
(formulation/ac or lb/ac)(days)

YesAsana XL5.8 - 9.6 oz21
YesBaythroid1.6 – 2.8 oz45
Nodimethoate1 pt21
NoLorsban 4E1-2 pts28
YesLannate WSP0.25 – 0.50 lb14
YesLannate LVv3/4 - 1 lb14
NoLarvin 3.2F18-30 oz28
YesMustang Max2.8 – 4.0 oz21
YesPenncap-M2-3 pts20
YesPounce 3.2 EC2-4 oz60
YesPounce 25 WP3.2-6.4 oz60
NoSevin XLR Plus0.5 - 1 qt21
NoSevin 80 S5/8 - 11/4 lb21
YesWarrior1.92 - 3.2 oz45


West Central REC celebrates 100 years September 17

Nebraska Congressman Tom Osborne will be the guest speaker at a celebration marking the centennial of the University of Nebraska West Central Research and Extension Center at North Platte on Friday, Sept. 17.

The event, which is open to the public, will feature demonstrations and tours of the center, as well as a complimentary lunch. A variety of exhibits will showcase research at the extension center. In 1903, legislation was passed and signed by Gov. John H. Mickey, which recommended that an agricultural substation be established in western Nebraska to “…determine the adaptability of the arid and semiarid portions of Nebraska to agriculture, horticulture and forest tree growing, such as the production of grain, grasses, root crops and fruits of the kinds commonly grown in such latitudes of other states, also the most economical methods of growing such crops without irrigation.” The land was purchased in 1904.

The importance of growing crops with irrigation and livestock’s value to the region led the center to expand its mission into these areas.

Today, researchers in the West Central district, which includes 20 counties, investigate both dryland and irrigated cropping systems, water use, soil fertility, weed management, horticulture, range management, beef systems and reproductive management, hydrogeology, forestry, 4-H and youth development, agricultural economics, and control of external livestock parasites.

The center, which is the oldest research and extension center in the state, was originally called the North Platte Substation and later renamed the North Platte Experiment Station in 1952 and the North Platte Station in 1966. It was given its current name, the West Central Research and Extension Center, in 1984.

The Centennial Field Day Sept. 17 will begin with registration and lunch at 11:30 a.m. CT at the center. The program is scheduled to begin at 12:15 p.m., followed by field demonstrations at 1 p.m. that will be repeated at 2 p.m.

John Owens, IANR vice chancellor and vice president, will speak at 3 p.m., followed by Congressman Osborne at 3:30. To RSVP for lunch contact Linda Lehmann by phone at (308) 532-3611, ext. 120, or by e-mail at llehmann1@unl.edu.

The celebration originally was scheduled for June 11, but was postponed because of the national day of mourning for President Ronald Reagan.

The WCREC is located 1.65 miles south of Interstate 80 on Highway 83 at North Platte.


Women In Ag Conference Sept. 16-17 in Kearney

Women will improve their business, management and financial skills while enhancing the well-being of their families and themselves at the Women in Agriculture: Today’s Critical Difference conference Sept. 16-17 in Kearney.

The conference, in its 20th year, offers educational opportunities to all women involved in agriculture and agribusiness as well as women landowners, said Beth Eberspacher, University of Nebraska program coordinator and organizer of this year’s event. Registration for the two-day conference begins at 9 a.m. Sept. 16 at the Kearney Holiday Inn. The conference concludes at 3:15 p.m. Sept. 17.

“The Women in Ag conference not only is an educational opportunity, but also a rejuvenating experience that provides the tools and strength for these admirable women to persevere yet another year in the challenging agricultural industry,” said Karrie Blake, who became the Women in Agriculture program coordinator in July 2004.

Keynote speakers include Sara Fogleman, extension agricultural economist, Kansas State University; Elbert Dickey, dean and director, Nebraska Cooperative Extension; Beth Birnstihl, assistant dean, Nebraska Cooperative Extension; Juli Burney, assistant professor of communication and theatre at Doane College in Lincoln; and Joan Burney of Hartington, counselor, columnist, public speaker and author.

Several workshops and informal group sessions will be offered: Marketing 101; Farm Accounting; Carbohydrates: Fact, Fallacy and Fun!; Landscaping; 12 to 24 Hour Vacations; Choosing the Right Business Entity; Achieving Life Balance; Income Tax Update; Ten Ways to Boost Profit; Ag and Water Law Update and more.

Registration is $75 by Sept. 3 and $85 afterward. The fee includes workshop materials, breaks, lunch and dinner on Sept. 16, and lunch on Sept. 17. For lodging, contact the Kearney Holiday Inn at (800) 248-4460. For more information or to register, contact Women in Agriculture, 303C Filley Hall, University of Nebraska-Lincoln East Campus, Lincoln, Neb. 68583-0922, call (800) 535-3456 or fax (402) 472-0776.

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