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Index

• Dear Reader
• Soybean Variety Selection is Critical for High Yields
• Choose the proper maturity
• Average Relative Yield Tables

Dear Reader,

In the next issue, I'll hit this seed quality issue pretty hard and review fungicide seed treatments.

If you know of anyone who would like to receive this newsletter, please let me know. I can put them on my mailing list. Be aware that all past issues are available on the Virginia Soybean website.

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Soybean Variety Selection is Critical for High Yields

Many have already made their variety selections and I hope information delivered at local County Extension meetings were of help. Still, with all of the available varieties, it is difficult to determine whether or not the right choice is being made. Virginia Tech annually conducts 12 replicated soybean variety tests in six regions of Virginia. These regions include the Northern Piedmont (Orange, VA), Southern Piedmont (Blackstone, VA), Northern Coastal Plain (Warsaw, VA), Southern Coastal Plain (Suffolk, VA), Eastern Shore (Painter, VA), and Southeastern Tidewater (Chesapeake, VA). While it is tempting only to use the results of the test closest to your operation, this is not usually a good idea. It is important that the variety chosen perform well under a number of different environments. Research has shown that highest yielding variety from a single location will always yield less at that same location the following year. In some cases, the highest yielding variety could even yield less than average. On the other hand, the highest yielding variety from multiple-location averages will usually result in high yields at any location in the following year. Therefore it is advisable to look at average yields across locations in addition to selecting varieties based on local yield data.

Multi-year averages give greater confidence to variety performance. The data presented on the following pages are an average taken from multiple-locations over the past four growing seasons. The list does not include all varieties that have been tested, but varieties with above-average yields that have been tested for at least 2 years in at least 6 locations. The higher the number of observations, the more confidence that the variety will perform as indicated. These data are not actual yield in bushels per acre, but an average relative yield compared to other varieties in the test location. Relative yield is calculated by dividing the yield of a variety by the average of all varieties at that location. Relative yields are then averaged across locations. Average relative yields take out some of the bias occurring when averaging over locations when all varieties were not tested at each location.

In addition to selecting varieties based on yield, one should note the herbicide or nematode resistance of the variety. If planting into a historically weedy or nematode-infested field, one should first make their selection based on the ability to control the weeds present and/or on resistance to nematodes. The yield data presented here were obtained from weed- and nematode-free conditions and are not intended to aid in variety selection under conditions of weed or nematode infestation.

Performance details of varieties tested in the Virginia Soybean Variety Evaluation Tests within each location are available at your county Cooperative Extension office or can be found on the web at: www.vaes.vt.edu/tidewater/soybean/variety.html

Before I proceed any further, we should first review steps in selecting the proper variety. I've already mentioned weed control being one of the most important; therefore, I'll not go into detail with Roundup-Ready or STS varieties. I'll first address selecting the proper maturity group

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Choose the proper maturity

Maturity is of utmost importance. In general, one should select a maturity group that will mature before frost, but produce adequate canopy to maximize yield potential. Maturity groups (MG) 3, 4, and 5 will meet these criteria when planted full-season. Late MG 5 or MG 6 varieties should be restricted to the southeastern portion or Eastern Shore of Virginia since they will not fully mature before frost in the western and northern parts of the state. Late 5's or early 6's should not be planted in a double-crop system due to a higher probability that the crop will be damaged by frost. Frost does more than defoliate soybeans; as long as there are still green pods on the plant, a frost will lower yield. Only after the R7 stage (physiological maturity), which is indicated by one normal pod on the main stem that has reached its final mature color (not yellow, but brown or tan), has the crop accumulated all its dry matter or seed weight. By this stage, very few leaves should be remaining. As occurred during the fall of 2000, frost will reduce seed size, therefore reduce yield. If experience indicates that frost is occurring before R7, then use an earlier maturing variety.

Will Early Production Systems Work in Virginia?

Will a MG 3 variety accumulate the needed leaf area to maximize yield potential in a full-season system? Our research indicated that it would usually accomplish this. However, other dangers exist by using MG 3 varieties. The first one has to do with drought avoidance. On average, we are more likely to avoid drought in eastern Virginia by planting a later-maturing variety, not an earlier one. Although you may hear a lot about the success of the Early Soybean Production Systems, or ESPS, in the mid-South, our research indicates that soybean yields with this system (planting an early maturing variety in April and maturing the crop in early September) are rarely competitive with planting a later MG in May. The sole reason seems to be that a MG 3 variety experiences more drought stress. In addition, we've found that seed quality rapidly deteriorates in September. This is not to say that such a system does not have a niche fit in some of Virginia ­ it does. But, it should not be used a method to improve yields. I've not investigated these systems under irrigation.

Which maturity group for Full-Season Systems?

The following suggestions are based primarily on yield potential, but other factors such as seed quality also influence my choice. In general a late MG 4 or MG 5 is the best choice in Virginia. Exceptions are: late MG 3 or 4 in the northern Piedmont and MG 3 or early 4 for the Shenandoah Valley. Although there have been reports of success using maturity group 3 varieties outside of the northern Piedmont or Shenandoah Valley, I do not recommend them because of the potential for poor seed quality (see Soybean Update, Vol. 5, No. 7). If growing cotton or peanuts, I recommend using only MG 5's. MG 4 varieties will mature in October, usually before or during cotton and peanut harvest. The longer these mature beans remain in the field during warm and humid conditions, the greater the likelihood of poor seed quality. Below are average yields of each maturity group at six locations over the past 5 years in Virginia.

Table 6.1. Average yields of soybean varieties tested in the 1998-2002 Virginia full-season variety tests.

		Maturity Group .
Location	No. Years	3	E4	L4	5	6
N. Piedmont	5	47.8	48.2	45.3	47.3	---
S. Piedmont	5	---	25.2	32.3	37.8	---
Eastern Shore	5	49.9	49.3	52.6	52.2	48.7
N. Coastal Plain	5	38.3	37.4	36.0	40.8	---
S. Coastal Plain	5	51.8	52.7	55.3	52.5	51.0
Chesapeake	5	---	52.2	58.0	55.6	46.2

A few comments should be made about the above locations. The Southern Coastal Plain and Chesapeake soils are classified as somewhat poorly or poorly drained. However, both soils are either artificially drained by ditches and/or tile drainage, making them very productive corn and soybean soils. Some drought stress is common on these soils, but usually not severe. Even in 2002, we averaged over 50 bushels/acre at both locations. When variety tests have been conducted on sandier, well drained soils in Suffolk, then the MG 5 varieties usually out-yielded the MG 4 varieties. The following table illustrates the effect of severe drought on yield.

Table 6.2. Average soybean yields in 2002 Virginia full-season variety tests.

	Maturity Group
Location	3	E4	L4	E5	L5	6
N. Piedmont	36.8	36.2	36.4	36.1	35.5	---
S. Piedmont	---	13.2	21.5	23.2	20.1	---
Eastern Shore	36.0	30.7	36.5	38.9	43.0	41.0
N. Coastal Plain	12.4	14.5	14.9	26.8	31.7	---
S. Coastal Plain	47.0	51.9	55.8	53.5	56.1	64.9
Chesapeake	---	49.7	51.5	56.6	49.5	49.4

In 2002, the later-maturing varieties had an advantage because the critical pod and seed development stages occurred later, therefore took advantage of September and October rains. Although 2002 was an unusual year and we would not plan on such low yields, the data above may better represent the response of maturity groups on droughty soils in Virginia.

Develop adequate leaf area for double-crop systems

A consideration other than drought avoidance and frost concerns must be taken into account for double-crop systems. This is canopy development. Unless a soybean crop can develop approximately 3.5 to 4.0 complete layers of leaves per area of land, the crop will not achieve its maximum yield potential. These "layers" of leaves can be best represented by an index called leaf area index, or LAI. An LAI of 4.0 is equivalent to a total of 4 sq. feet of leaves per sq. foot of ground (or 4 acres of leaves per acre of ground). Over the past 5 years, we have collected a wealth of information validating the leaf area-yield relationship. In double-crop systems, leaf area commonly limits yield. Therefore strategies to increase and protect leaf area on less productive soils are usually beneficial. A later-maturing variety will produce more leaf area because it is in the vegetative stage for a longer period. Therefore, there is less risk of inadequate leaf area for later-maturing varieties. This concept of adequate leaf area is revealed in average yields of varieties grown in a double-crop system.

Table 6.3. Average soybean yield in the 1998-2002 Virginia double-crop variety tests.

		Maturity Group.
Location	No. Years	3	E4	L4	5
N. Piedmont	4	39.8	39.8	38.4	34.8
S. Piedmont	3	---	24.6	30.2	31.3
Eastern Shore	5	33.0	38.8	37.8	42.3
N. Coastal Plain	5	30.7	35.5	35.0	35.4
S. Coastal Plain	5	30.8	34.4	36.5	39.8
Chesapeake	5	---	38.3	37.0	36.4

In double-crop soybeans, we are pushing the maturity date back about 1 to 2 weeks because we are planting later. Therefore, we need to tweak recommendations a little. In general, we can back off the full-season recommendations by about 1/2 of a MG. Don't use MG 6 varieties due to frost concerns in any part of Virginia. In the northern Piedmont and Valley, don't use an early or late MG 5 for the same reason. Part of the explanation that some late MG 5 varieties perform well in full-season tests in Virginia and not double-crop test is related to their later relative maturity. In other words, these late MG 5 varieties are likely to suffer yield reductions due to frost in double-crop systems, but not full-season systems. Experience on your farm or in your area should be used to guide your decision in selection of maturity groups for double-crop. The same rule applies: Use the latest MG that will not be affected by fall frost to maximize leaf area and yield potential. I will remind you again that if frost occurs before the R7 development stage (when one pod on the plant has reached its final mature color), yield loss will occur. In most of Virginia, a MG5 will, on average, out-yield a MG 4 when planted double-crop. But this is not always the case. Situations where earlier maturity groups do just as well are on our more productive soils that allow adequate leaf area development. Our Chesapeake location is a good example of this. These soils are wetter and a little higher in organic matter; in general, very good corn and soybean soils due to fewer drought events.

Below are average yields during 2002 during severe drought stress. Again, note that the later maturity groups waited on late-September and October rains.

Table 6.4. Average soybean yields in the 2002 Virginia double-crop variety test.

	Maturity Group
Location	3	E4	L4	E5	L5
N. Piedmont	---	20.6	35.1	---	---
S. Piedmont	---	---	---	---	---
Eastern Shore	32.7	36.3	35.5	37.1	36.2
N. Coastal Plain	16.0	19.2	19.7	22.1	23.3
S. Coastal Plain	12.4	22.1	21.0	24.3	29.6
Chesapeake	---	15.9	13.8	21.8	18.4

Soil type matters

When will early MG's equal or out-yield later MG's? When the soil or rainfall pattern (basically soil moisture) allows the crop to develop adequate canopy. In this case, an early MG (MG 4 in eastern or southern Virginia, MG 3 in northern Piedmont or the Valley) with better genetic yield potential can out-yield a later MG. Therefore soil type is an important consideration when selected double-crop varieties. If the soils yield potential is low, say 20 to 30 bu/A (Rumford, Bojac, Cecil, etc.), then a later maturing variety would better avoid drought and have a longer time to develop adequate leaf area. On the other extreme, a 40-50 bu/A soil with good water holding capacity (Pamunkey, Wickham, State, Davidson, etc.) will likely produce as good of yields from an early as a late variety. For 30-40 bu soils (Emporia, Eunola, Suffolk, etc.), its pretty much a crap shoot depending on how much rain Mother Nature gives us.

Nematode and Herbicide Tolerance

In many cases, soybean varieties should be selected primarily on factors other than yield. Weed and nematode infestations are good ones. The arrival of herbicide-tolerant crops has made weed management much easier and reliable. The presence of weeds can do much more damage to crop yield than poor variety selection (based on yield). Therefore, don't hesitate to use the new technologies if needed.

Determining whether to use an herbicide-tolerant variety is usually easier than determining to use a nematode-tolerant variety. Weeds are much more visible from the windshield. Still, most of us can recognize a nematode infested field near the end of the growing season, although we may not know the problem is nematodes. In many cases, these fields look worse that a weed-infested field and may be just as yield robbing. Therefore, test the soils for nematodes if you suspect a problem. Fall is the best time to do this because nematode populations usually fall dramatically during the winter. Yet, spring is not too late to sample. One thing is for sure. If you have high spring counts, then you definitely need to address the problem.

Of course, the first line of defense is rotation to a non-host crop. If cyst nematode is a problem, then rotation to any crop is effective. However, if root knot is the problem, then it's not as easy. Southern root knot can use corn and cotton as an alternative host, but northern root knot uses only peanut as a host. Regardless, if soybeans must be planted select the appropriate variety. Unfortunately, with the exception of soybean cyst nematode, little is known about the resistance of soybean to other nematodes. The tables on the following pages list those varieties with soybean cyst and root knot nematode resistance.

On the following pages are lists of varieties available in Virginia that have yielded greater than average in the Virginia variety tests over the past 4 years of testing. In addition, I've listed some promising new varieties that I've only tested in limited location in 2002. Note that yields listed are relative yields, not actual yield. Remember, the more observations, the more confident that I am in that variety performing as well next year, regardless of location.

In summary, there are several factors that go into selecting the appropriate soybean variety. I've listed a few of the most important here. In reality, variety selection is very site specific. Knowing weed, nematode, and other pest problems will narrow one's choices rapidly. Choose the proper maturity for your area and field. Then use the tables on the following pages to select a variety that has consistently yielded greater than average over multi sites and years.

More detailed information on Virginia soybean varieties can be found in the following publications:

Characteristics of Soybean Varieties Grown in Virginia. 2003. Tidewater AREC Info. Series No. 457.

Average Relative Yields of Soybean Varieties Tested in the Virginia Official Variety Tests 1999-2002. Tidewater AREC Info. Series No. 456.

Virginia Soybean Variety Evaluation Tests 2002. Tidewater AREC Info. Series No. 454.

All of these publications can be found at the Virginia Soybean Production website: http://www.vaes.vt.edu/tidewater/soybean/variety.html

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Average Relative Yield Tables

Table 6.5.2. Average relative yield of maturity group III soybean varieties grown double-crop and tested in at least 6 locations over the last four years (1999-2002).

			Nematode Resist.
Brand	Variety	Herbicide Resistance	Cyst	Root Knot	Average Relative Yield	No. of Observations
S. States	RT-3975	RR			103	33
S. States	SS-381-STS	STS			102	33
Other promising new varieties (tested in less than 5 locations)
S. States	RT-3802N	RR	R3,14		102	9
S. States	RT-3702	RR			101	9
S. States	RT-3799N	RR	R3,14		100	9

Table 6.5.3. Average relative yield of maturity group IV soybean varieties grown full-season and tested in at least 6 locations over the last four years (1999-2002).

			Nematode Resistance
Brand	Variety	Herbicide Resist.	Cyst	Root Knot	Average Relative Yield	No. of Observations
DPL	DP4748S	STS			111	24
DPL	DP4690RR	RR			109	42
DPL	DP3478				107	18
USG	7489RR	RR			107	18
Public	Manokin		R1,3	Rai	106	45
Pioneer	94B53		MR3,14		106	18
S. States	RT-4980	RR			105	42
DPL	SG498RR	RR			105	39
Asgrow	AG4403	RR	MR3		105	24
Delta King	DK4868RR	RR	R5		104	42
S. States	SS-493				104	27
Vigoro	V462NRS	RR/STS	R3,MR14		104	18
Dekalb	DKB44-51		MR3		102	33
Vigoro	V442NRR	RR	MR3,14		101	21
Other promising new varieties (tested in less than 6 locations)
Hytest	HTS 4725RR	RR			108	6
S. States	RT-4502N	RR	R3,14		108	12
NK	S40-R9	RR	R3,MR14		107	9
S. States	RT-4810N	RR	R3,14		106	15
S. States	RT-4702N	RR	R3,14		104	15
Vigoro	V47N3RR	RR	R3,MR14		104	9
Agway	APK432NRR	RR	...		103	9
Delta King	DK4763RR	RR	R3,MR14		101	9

Table 6.5.4. Average relative yield of maturity group IV soybean varieties grown double-crop and tested in at least 6 locations over the last four years (1999-2002).

			Nematode Resistance
Brand	Variety	Herbicide Resistance	Cyst	Root Knot	Average Relative Yield	No. of Observations
DPL	DP4690RR	RR			113	30
S. States	SS-493				109	27
Pioneer	94B53		MR3,14		106	24
S. States	RT-4980	RR			104	45
S. States	SS-439				104	39
Delta-King	DK4868RR	RR	R5		103	36
DPL	SG498RR	RR			103	36
DPL	DP4344RR	RR			102	21
Public	Manokin		R1,3	Rai	101	60
Other promising new varieties (tested in less than 6 locations)
Stine	S4882-4	RR	R3,MR14		117	9
Pioneer	94B73	RR			108	12
S. States	RT-4810N	RR	R3,14		107	12
Vigoro	V462NRS	RR/STS	R3,MR14		106	9
Garst	4512RR/N	RR			104	15
Agway	APK432NRR	RR	C3		103	6
Vigoro	V442NRR	RR	MR3,14		102	9
S. States	RT-4702N	RR	R3,14		102	12

Table 6.5.5. Average relative yield of maturity group V soybean varieties grown full-season and tested in at least 6 locations over the last four years (1999-2001).

			Nematode Resistance
Brand	Variety	Herbicide Resistance	Cyst	Root Knot	Average Relative Yield	No. of Observations
USG	5601T				109	27
Public	Hutcheson		T		107	96
DPL	DP5110S	STS			106	24
USG	510nRR	RR	MR3,14		106	18
Pioneer	9594			Ri	105	18
S. States	SS-5200-STS	STS			104	48
USG	540nRR	RR	MR3,14		104	27
Pioneer	95B32	RR	R3,14		102	42
Delta King	DK5961 RR	RR	R3,MR5,14		102	30
S. States	RT-517N	RR	R3,14		101	42
DPL	DP5806RR	RR	MR3,14		101	27
NK	S52-U3	RR	R3,9,14		101	27
Other promising new varieties (tested in less than 6 locations and 2 years)
NK	S56-D7	RR			110	9
USG	7582nRR	RR	R3		108	9
Pioneer	95B96	RR		MRi	107	6
Asgrow	AG5903	RR	R3,14		107	3
Montague	MFL-159				106	6
Asgrow	AG5603	RR	R3		103	6
Asgrow	AG5301	RR	MR3,14		101	6

Table 6.5.6. Average relative yield of maturity group V soybean varieties grown double-crop and tested in at least 6 locations over the last four years (1999-2002).

			Nematode Resistance
Brand	Variety	Herbicide Resistance	Cyst	Root Knot	Average Relative Yield	No. of Observations
S. States	SS-5200-STS	STS			110	39
DPL	DP5110S	STS			109	18
Public	Hutcheson		T		107	69
Pioneer	95B33		R3,MR14	MRi	106	18
Public	Anand		R3,5,14		103	48
NK	S57-A4	RR	MR3,9,14	Ri,MRj	103	33
DPL	DP5655				103	27
Pioneer	9594			Ri	101	21
Other promising new varieties (tested in less than 6 locations and 2 years)
DPL	DP5915RR	RR	R3,MR14		109	6
Virginia	99VPI-67	RR			108	9
S. States	RT-5999N	RR	R3,14		106	15
Virginia	99VPI-120	RR			105	9
Vigoro	V562NRR	RR	R3,MR14		104	3
S. States	RT-5602N	RR	R3,14		103	6
Montague	MFL-159				101	6

Table 6.5.7. Average relative yield of maturity group VI soybean varieties grown full-season and tested in at least 6 locations over the last four years (1999-2002).

			Nematode Resistance
Brand	Variety	Herbicide Resistance	Cyst	Root Knot	Average Relative Yield	No. of Observations
Pioneer	96B21	RR		MRai	113	18
Hartz	H6255RR	RR			105	18
Other promising new varieties (tested in less than 6 locations and 2 years)
Public	NC ROY				107	9
Asgrow	AG6202	RR	MR3		100	9

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Sincerely,

David L. Holshouser

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