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Index

• Dear Reader
• Don't be into a hurry to plant in 2003
• Use Good Weed Management Practices to Minimize Weed Resistance
• Seeding Rates Revisited
• Managing Deer Damage
• Suggested Soybean Seeding Rate Chart
• American Soybean Association News

Dear Reader,

Planting is probably one of the most important times of the year. Unless we take the time to insure a good, uniform stand, we are not likely to maximize yield potential. With the introduction of genetically-engineered crops, seed costs have become one of our biggest inputs. Replanting, especially in a year when seed are in short supply, could be devastating to your bottom line. Therefore, slow down, check seeding depth and seed spacing often, and wait until soils are warm before planting.

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Don't Be in a Hurry to Plant in 2003

Planting Date - How important is it? In 2003, it may be more important than in the past. Why? The main reason is the same old problem that we've been trying to address since last year's harvest - seed quality. In Soybean Update Vol. 5 No. 7, I addressed the seed quality problem in detail. I expanded on the subject in the last issue with seed treatment information. Past issues can be found on my web site: http://www.vaes.vt.edu/tidewater/soybean/soybeanup/soybeanup.html . I won't go into the detail that I have in previous issues, but do want to emphasize some practical, non-chemical methods of avoiding seedling disease and stand problems.

We continue to collect data that indicates that good uniform stands are important for maximum economic yields. Fungicide seed treatments will help achieve this, but the longer the seedling remains below the surface, the more likely that seedling diseases will occur and stands will be reduced. Therefore, the most important step to reduce seedling disease is to get the plant up and out of the soil quickly.

This brings me back to planting date. There's a tendency for all of us to be timely and efficient in all we do. This is usually good. But patience can be a great virtue as well. In 2003, when seed quality of nearly all varieties is questionable, waiting patently for the soils to warm up to 65O F (at a 3-inch depth) and stabilize at that temperature should pay off.

Although at the moment, we are experiencing very warm temperatures and emergence would be rapid under those conditions, experience tells us that cooler temperatures are right around the corner. Watch the weather forecast. If a cold front is predicted, especially when accompanied by rain, then hold off until it begins to warm up. I know it's hard to do this when conditions at the moment are good. But, a combination of poor seed quality with cool soils is a great recipe for insuring that replanting of some high-priced seed will occur. Don't be overly concerned about planting late; large yield losses from late planting do not occur unless delayed after mid-June.

Furthermore, the best varieties have been taken. Good luck in finding the same, high-yielding variety to replant with. There seems to be lots of older, lower-yielding varieties available; but few of the higher yielding ones. So, you would have a yield loss in addition to additional seed costs with replanting. Don't risk it.

Planting date is one consideration; equally important is seed placement and soil-to-seed contact. Plant the seed about 1-inch deep. Seed at a 1 1/2 -inch depth will delay emergence and likely result in poor stands. If no-tilling, then cut the residue; penetrate to the proper depth; and close the seed furrow completely. Don't hairpin any residue.

In summary, patience should definitely pay off this year. Don't get into a hurry to plant in early May. Plus, take your time when planting to insure proper seed placement and soil-to-seed contact.

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Use Good Weed Management Practices to Minimize Weed Resistance

Kevin Bradley, Postdoctoral Research Associate, Virginia Tech - Eastern Shore AREC

Since their introduction, the acreage of soybeans planted with Roundup Ready® varieties in the United States has risen from 2% in 1996 to 68% in 2001 (USDA 2001). As growers continue to adopt the Roundup Ready® technology and make applications of glyphosate in the same fields year after year, the likelihood of weeds developing resistance to glyphosate increases dramatically.

Glyphosate-resistant goosegrass, rigid ryegrass, and Italian ryegrass biotypes have already been identified in areas outside of the United States. A number of glyphosate-resistant marestail biotypes have also been identified in the eastern United States, including one biotype from the eastern shore of Virginia.

Initial investigations of this biotype and evaluations of various marestail burndown programs have revealed that excellent marestail control can be achieved with fall or early preplant applications of Canopy XL®, 2, 4-D, or 2, 4-D plus Gramoxone Max®. Once marestail rosettes exceed 3 1/2 inches in diameter and/or stems begin to elongate, however, marestail control decreases significantly with either of these herbicide programs. For this reason, marestail size at the time of herbicide application is one of the most important components of a successful control program.

Many weed scientists in the United States have speculated that other troublesome weeds that produce large numbers of seed like lambsquarters, pigweed, and Italian ryegrass will eventually develop resistance to glyphosate if the current trend in glyphosate use continues.

Soybean growers should make every effort to prevent this from occurring. This can be accomplished by rotating herbicide modes-of-actions from one year or from one crop to the next. For example, the use of the herbicide programs described previously provides soybean growers with modes-of-action unlike that of glyphosate and will provide effective marestail control. Similar strategies can be adopted with other weed species. Other strategies that soybean growers should consider to prevent resistant weed development include tank-mixing other herbicides (and other modes-of-action) with glyphosate, rotating to conventional soybean varieties on a regular basis, and rotating to other non glyphosate-tolerant crops on a regular basis.

Finally, not overusing a single mode of action within a growing season, as is possible with Roundup Ready® soybean, should be stressed. If using glyphosate as the primary weed control agent in the crop, then using a different mode of action to burndown existing weeds in a no-till system just makes good integrated weed management.

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Seeding Rates Revisited

Use past experience to determine if you have adequate leaf area to maximize yield. The appropriate seeding rate to give the highest yields will vary depending on planting date, row spacing, and soil type; all of which depends on the ability of the crop to develop approximately 3.5 to 4.0 complete layers of leaves by the flowering stage (I've spoke of this concept in the past as leaf area index or LAI). If a crop can develop this amount of leaf area by this development stage, then further yield increases will not be realized by increasing plant populations.

Past experience may be the best tool to decide on the appropriate seeding rate (and row spacing). If, in the past, soybeans do not consistently close their canopy by the flower stage (R1-R2) in a particular field, then this field is a good candidate for increasing seeding rates and/or narrowing rows. On the other hand, if lodging has been a consistent problem, then lower the seeding rate.

If you have questions regarding how to visually determine adequate soybean LAI, refer to Virginia Cooperative Extension publication 444-203, "Identifying soybean fields at risk to leaf feeding insects" written by Drs. Ames Herbert and Sean Malone, Mr. Brian Jones, and me. Although the publication's emphasis is defoliating insects, it includes several photographs of varying levels of soybean leaf area. The publication can be found on the web at: http://www.ext.vt.edu/pubs/entomology/444-203/444-203.html .

Planting date has an effect on leaf area development in Virginia. May plantings have little trouble reaching the "critical" level. However, as the growing season is shortened as planting date is delayed; the amount of leaf area will be less. Less leaves to capture sunlight results in lower yield. The best way to compensate for this lost leaf area is to narrow rows and increase plant population. Narrowing row spacing will generally give yield increases regardless of planting date, but greater advantage will be realized as planting date is delayed. Therefore, row spacing for double-crop plantings should never exceed 24 inches.

Maturity group (MG) should also be figured into seeding rate decisions, especially if late planting occurs. An earlier maturing variety, like a late planting date, will not produce as many leaves as a later maturing variety. In general, Virginia producers should plant a MG 4 or 5. MG 4 will produce less leaf area than 5's, but MG 4 usually produces enough LAI. However, I don't recommend MG 4 in the cotton/peanut growing areas. These varieties will mature in early- to mid-October, when peanut and cotton harvest is taking place. Leaving mature soybeans in the field during hot and humid periods will seriously degrade seed quality. Only use MG 4 varieties if you can harvest in a timely manner.

I continue to get questions about MG 3 (or earlier) varieties. They can be grown in Virginia, but may not produce enough leaf area at standard seeding rates. If using MG 3, increase the seeding rate by 10 to 20%. Also, these varieties will mature in mid- to late-September if planted in May. Therefore harvest quickly to prevent seed quality problems.

The correct seeding rate will depend on soil type also. After evaluating the past history of the field and making MG and row spacing decisions, you must choose the plant population to be used. Plant population has received much more attention since the advent of Roundup-Ready soybean and the higher seed prices that go with this technology. Experience and years of research have indicated that full-season plantings in Virginia only require a final plant population of 100,000 to 140,000 plants per acre. But double-crop plantings will require plant populations of 180,000 to 220,000 plants per acre. But, you may ask, why the wide range in the recommended populations? Planting the lower end of the range could reduce total amount of seed used by 40,000 per acre (12 to 14 pounds); this could save $6 to $7 per acre on Roundup-Ready seed. So, why not just use the low end of the scale?

The problem is that the amount of leaf area development will depend on the amount of rainfall received in the vegetative stages and the ability of the soil to hold water. We cannot predict the rainfall; therefore the amount of growth from year to year will vary substantially. But, we have a relatively good idea of how well a particular soil will hold water. A soybean crop grown on a sandy soil with very low water holding capacity will have trouble meeting its leaf area requirements. Therefore, higher populations will allow the crop to use available water resources early to produce a larger canopy. In contrast, a crop grown on a soil with higher water holding capacity will require fewer plants to produce the necessary leaf area.

2001 Virginia research indicated that soybean yielded 10-15% less when the plant population was reduced to the low end of the scale but the higher end of the scale was needed. This was on a sandy soil with low water-holding capacity. Although the seed costs were higher, the increase in yield resulted in a higher net return. Last year's drought seemed to confirm the above research. In most cases, the critical LAI level was not met and yield continued to increase with increasing plant population.

On the following page is suggested soybean seeding rates for Virginia. Use the following guidelines to decide on which final plant population to use:

General Guidelines

• Adjust the seeding rate (seeds per foot) for % emergence. Although 85% emergence (assumed on the chart) can be obtained with high quality seed and accurate seed placement, certain conditions will lead to lower emergence. This year's seed quality problems will likely result in lower % emergence. See the formula below the chart to calculate the rate.
• Increase seeding rate 10-15% if a drill is used. This is due to the poor seed distribution from drills that results in gaps in the stand. If a "precision" drill that meters the seed is used, then no adjustment is needed.

Full-Season Guidelines

• In 30-36" rows, use the 100,000 or 120,000- plant population rate; higher rates will result in lodging and inter-plant competition.
• Use the 100,000-plant population rate only on the most productive soils (40+ bushel yield potential)
• Use the 140,000-plant population rate on soils of low water-holding capacity to insure adequate leaf area.
• As planting date is extended into June, use higher rates.

Double-crop Guidelines

• For soybean following barley (early-June plantings), plant population can be reduced by 20-30,000 plants/acre.
• Only use the 160,000-plant population rate on very productive soils such as Pamunkey, Davidson, State, Wickham, or other soils with high water-holding capacity and only if planted in June.
• Use the 180,000 plant-population rate for most soils if planted in June; use 200,000-plant population rate for sandier, low water-holding capacity soils.
• As planting moves into July, increase the seeding rate by enough seed to insure a 20,000 plants/acre increase in plant population. Increase again for late July.

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Managing Deer Damage

There are a few things that can be done now that will reduce yield loss. For all intents and purposes, you have to offer the deer more than they can eat. I don't mean feed them like you would feed cattle, but to make sure that there is enough plant material in the field to tolerate feeding and still produce enough foliage to yield well.

Damage to young seedling plants is not as yield-robbing as damage at later stages. Unless deer are also feeding heavily during the pod and seed fill stages, the soybean crop has the potential to recuperate and produce a decent yield. Of course, this depends on rainfall, soil type, etc. Research from Clemson University proves this point.

Source: Clemson Extension Publication IL 59 (June 1996), Strategies for Reducing Deer Damage to Soybeans.

Influence of clipping at various growth stages on yield and height of "Hagood" soybeans, Pendleton, SC. Values are 2-year averages (1993-94).

V4	V6	V10	R4	Yield (bu/A)	Height (in.)
-	-	-	-	40.2 a	37.0 a
+	-	-	-	40.2 a	33.1 b
-	+	-	-	39.7 a	29.0 c
-	-	+	-	40.9 a	27.2 cd
+	+	-	-	41.8 a	26.5 cd
+	-	+	-	40.8 a	22.4 ef
-	+	+	-	36.0 a	20.7 fg
+	+	+	-	39.7 a	20.9 fg
+	-	-	+	26.7 b	24.4 de
-	-	-	+	24.0 bc	29.2 c
-	+	-	+	21.2 bc	22.5 ef
-	-	+	+	20.8 bc	22.1 ef
+	+	-	+	18.5 bc	17.9 gh
+	-	+	+	16.3 c	16.8 hi
-	+	+	+	16.5 c	15.5 hi
+	+	+	+	16.4 c	14.4 i

If you have experienced heavy deer predation in the past, then plant in narrow rows at high populations. If only a portion of the field has been historically damaged, then ramp up the population in that part of the field. The use of high populations and narrow rows would be especially beneficial if a small field is surrounded by woods on 3 or 4 sides.

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Suggested Soybean Seeding Rates

Seeding Rate = Desired plant population ÷ (43,560 sq. ft./acre ÷ row width in ft.) ÷ % emergence

Example: = 140,000 ÷ (43,560 ÷ 1.25 ft.) ÷ 0.85
= 140,000 ÷ 34,848 ÷ 0.85
= 4.7 seeds per foot on 15" rows

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American Soybean Association News

Date Posted: 4/29/2003

April 24, 2003... Saint Louis, Missouri... The American Soybean Association (ASA), a trade group that represents 26,000 U.S. soybean farmers, has called for greater measures to safeguard 72 million acres of domestic soybean production from Asian rust disease. ASA and the Animal and Plant Health Inspection Service (APHIS) of the United States Department of Agriculture (USDA) have had a series of ongoing meetings about the rapidly increasing prevalence of rust in South America.

Early this month, ASA leaders again met with APHIS Administrator Bob Acord and other APHIS officials to discuss appropriate safeguards necessary to prevent the introduction of rust spores into the United States. Accompanying the ASA leaders was Dr. Michael McNeill, a researcher who has worked on soybean rust for the past 30 years. "Due to low ending stocks of domestically produced soybeans, I'm particularly concerned that some companies may seek to import whole soybeans from South America where soybean rust has progressed significantly in the last two growing seasons," said ASA First Vice President Ron Heck, a producer from Perry, Iowa. "ASA has urged APHIS to implement a rigorous inspection and quarantine process to safeguard U.S. soybean production. If determined necessary by pest risk analysis, APHIS should implement a prohibition on whole soybean imports, and adequate inspection and processing procedures for soybean meal."

Soybean rust attacks the foliage of a soybean plant causing the leaves to drop early, which inhibits pod setting and reduces yield. The amount of damage depends on how early in the growth of the soybean plant the infection occurs. An infection in mid-September would probably cause minimal losses compared to an introduction in mid-July, when it could be devastating.

"It is possible for soybean rust to be introduced into the U.S. through shipments of whole soybeans from South America," Dr. McNeill said. "I recently returned from Brazil where I found evidence of rust in growing areas southwest of Sao Paulo, in central and central west areas, and in a small area north of the Amazon River."

There is the potential for a natural introduction of soybean rust into the United States that would likely result from spores being carried on wind currents or storms from West Africa or northern South America and the Caribbean. However, ASA is also concerned about the immediate risk of human assisted movement of soybean rust that could occur as a result of imported plant materials infected with the disease. Imported whole soybeans are allowed to contain up to 2 percent foreign material that mostly consists of pieces of plant stems, pods and leaves capable of transmitting the rust spores.

In a Phytosanitary Alert issued in February by the North American Plant Protection Organization (NAPPO), it was estimated that soybean rust could adversely affect all soybean varieties in the United States at an estimated cost of $7.2 billion, which represents about half the value of the U.S. soybean crop.

"During the course of our discussion, APHIS officials indicated they would examine requiring any shipments of whole soybeans to the U.S. to be quarantined for a sufficient period to prevent transmission of rust disease," Heck said. "APHIS has the authority under the Plant Protection Act to control the importation of commodities that may serve as a pathway for the introduction of foreign plant diseases. ASA supports a rigorous inspection and quarantine process to safeguard domestic soybean production from infection."

Although rust resistant soybean varieties would be the most economically viable solution, there is little resistance in the commercial varieties currently grown in the United States. In a December 2002 statement, the International Association for the Plant Protection Sciences (IAPPS) said that the availability of rust resistant soybean varieties in the United States is probably five to seven years away.

"ASA has met with USDA researchers and officials to urge that research efforts be accelerated," Heck said. "In the meantime, we must do everything possible to minimize the risk and delay the potential introduction of soybean rust in the U.S. to give plant breeders the time they need to develop rust resistant varieties."

Costly fungicide treatments currently represent the only option for containing soybean rust. ASA and APHIS discussed the fungicide products that are currently approved for treating soybean rust, and the high cost of controlling the fungus once it is established. According to USDA, eradication would not be technically possible because the disease has many uncultivated host plants that grow in the United States. Green bean, kidney bean, lima bean and cowpea producers would also experience losses.

"APHIS appeared to be prepared to consider destroying any small infestations that may occur as a preferable means of ensuring the disease is not able to spread during treatment," Heck said. "We asked APHIS to review their monitoring and protection measures, and they acknowledged that ASA and Dr. McNeill had provided information requiring a possible tightening of restrictions."

Dr. McNeill also indicated that he and other researchers have been working to detect the canopy reflectance signature of soybean rust by satellite as a better means to rapidly identify and prevent its spread. APHIS officials expressed interest in this work, and agreed to continue to share information with ASA and Dr. McNeill on rust detection and treatment methods in the future.

"ASA established with APHIS an ongoing process for sharing information and discussing further actions," Heck said. "I want to compliment APHIS on their past vigilance and their continuing efforts to work with ASA. Working together I hope we can prevent rust from becoming a serious problem in the U.S."

For more information contact:

Ron Heck, ASA First Vice President, 515/275-2853, checkers@netins.net
Dr. Michael McNeill, 515/295-5513, agadvis@ncn.net
Bob Callanan, ASA Communications Director, 314/576-1770, bcallanan@soy.org
Access this release at www.soygrowers.com

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Sincerely,

David L. Holshouser

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