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Our season is coming to a close. We seem to have survived an onslaught of soybean rust. We have not found any more rust spores in any of our traps since we discovered those six spores in Suffolk in mid-August. Unfortunately the media (both Ag and non-Ag) made more of this than we wanted. But, things seem to be getting back to normal. Although rust may not be much of an economic concern for Virginia anymore, aphid is present and numbers are increasing in some areas. Drought has ravaged many areas; others have had excessive rain.
Take note of the article by Dr. Katy Martin-Rainey, our new soybean breeder. She's looking for feedback from you regarding her breeding program. I look forward to new developments from that program.
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With all the talk about soybean rust, some may have forgotten that Virginia is also susceptible to another pest that can be nearly as damaging. It's not a pest that we are still waiting for to move into Virginia. It's one that's already here and has already increased production costs for some producers. The pest is soybean aphid.
Although soybean aphid is not as problematic for us as it is for Midwestern growers, it has become an annual occurrence. Fortunately, it stayed away for most of the summer and didn't rear its head until just recently. However, we now seeing it in most fields that we check.
Aphid populations have been suppressed for much of the summer by unusually hot weather, but populations can increase with cooler temperatures. When daytime temperatures are in the mid to low 80s and nighttime temperatures are in the mid to high 60s (which is common for much of September) soybean aphids can reproduce rapidly. Aphids might be a bigger problem in the double crop system because they provide a more attractive food source late in the season compared with full season beans that are more mature. Double crop fields should be scouted until they reach growth stage R6. We recommend using products that also provide good levels of corn earworm control, for obvious reasons. We also recommend using the highest labeled rate for whatever product is chosen (check the product label). A higher rate will provide the longest residual activity; up to 7 days or so in the absence of a lot of rain.
We continue to scout weekly for soybean rust and aphid. The map above shows average numbers of aphids from our survey as of September 2. As in years past, higher populations are further north. Of the fields that we've scouted, populations have not reached threshold of 250 aphids per plant. However, some fields have reached threshold populations. For example, we know of fields in Essex, Henrico, New Kent, and Westmoreland that required treatment.
For up-to-date information on this and other insect pests, log on to the Virginia AG Pest Advisory at www.sripmc.org/virginia.
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I started as the soybean breeder at Virginia tech in April, and since then I have met many people in the Virginia soybean industry, in Blacksburg, Corbin Hall, Warsaw, Montross, and elsewhere. The support within the state for the soybean breeding program is vital, and highlights the strength of the industry and the importance of agriculture here. Due to the state's special market position, this public soybean breeding program can make significant contributions to industry, and I am excited to be part of a strong Virginia soybean industry through variety development and innovation in other areas.
Development of varieties for Virginia is a continued emphasis in the breeding program, and some of you have already suggested traits that are needed in new public varieties. Insect and nematode resistance, STS and Roundup varieties, and more options with Group IV maturity have all been suggested. I encourage people to please contact me (kmrainey@vt.edu, 540-231-6496) with input in this regard, or to pass ideas on to David Holshouser. Such communication is key to a successful breeding program that serves the Virginia soybean industry.
Soybean rust is a concern, and researchers at Tech, including the breeding program, are addressing this threat. Virginia Tech soybean germplasm possesses valuable disease resistance that could potentially be developed into rust resistant varieties. Dr. Glenn Buss' excellent germplasm is the foundation of the breeding program, and many of his projects and objectives will, of course, continue under my guidance.
The program will soon be given a lab in the new Agriculture and Natural Resources Building under construction on campus, which will allow us to explore and utilize tools to accelerate the breeding process. In the new lab we will select traits such as rust resistance using DNA markers, and collaborate with other researchers. The ability to use molecular markers will allow the program to develop diverse objectives, breeding RR, conventional, and value-added germplasm and varieties, more efficiently. So the program will integrate new technologies and information into the tradition of plant breeding. Again, there are unique opportunities present in this program.
As I become familiar with the breeding program in the 2005 season I have learned plenty, and I have been patiently assisted by Dr. Buss, and the excellent people working at the Eastern Virginia Agricultural Research and Extension Center in Warsaw, the VCIA, and at the College Farm in Blacksburg. Their efforts are also vital to the success of the soybean breeding program.
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So, what happened to those spores? That's a question that I continue to get. I originally stated that 1) although the spores looked like soybean rust spores, we could not say for sure that they were soybean rust spores and not just spores from another rust; or 2) if they were rust spores, they would probably not have survived the extreme heat that we were having the week of deposition. Either way, rust has not manifested itself in Virginia.
But, we wanted proof, so plots near the spore trap were scouted and leaf samples taken by Drs. Pat Phipps and Darcy Partridge of the Tidewater AREC for serological tests. These tests allow us to detect soybean rust on leaves that do not have any signs or symptoms. All tests turned up negative. Below are the latest results from leaves sampled from several plant disease research plots.
Summary: a total of 90 leaf samples have been tested to date and all have been negative. Each run included a negative and positive control. The positive control was always positive and the negative control was always negative. Test works very well, but does take a half day to run after the collection of samples.
Although we continue to find new and interesting "look-alike" diseases on the soybean leaves our scouts bring back to the lab, none have turned out to be soybean rust. So, I think that we can safely say that soybean rust has not established itself in Virginia (as of Labor Day).
Did Hurricane Katrina bring rust spores north? I imagine that Hurricane Katrina was instrumental in spreading soybean rust further north. However, the hurricane's path was generally to our west. So I wouldn't expect a big flush of rust showing up in Virginia in the next couple of weeks. Still, I do expect some new discoveries in states that have not yet found the disease in the near future. Will Virginia be one of those new discoveries? We'll just have to wait and see.
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So, here are some general guidelines for estimating soybean yield. However, be aware that estimating yields is inaccurate unless detailed sampling is done late in the growing season. Estimates are usually not very good until the soybean approaches physiological maturity (R7). Less than 25% of the total seed dry matter has accumulated by the R6 development stage; only 50% has accumulated by R6.5. Stresses during the R6 to R6.5 stages can result in large yield losses mostly by reduced seed size, but also by reduced pods or beans per pod. After R6.5, stresses will cause a much smaller loss. For a review of soybean development stages, refer to the Iowa State's "How a Soybean Plant Develops" at http://www.extension.iastate.edu/pages/hancock/agriculture/soybean/bean_develop/bean_toc.html.
To estimate yields, follow the steps below. Be sure to sample in 5 to 7 different areas of the field.
1. Determine the number of row feet needed to make 1/1000th of an acre from the table below. In narrow rows, one may use 3 or 4 side-by-side rows instead of one long row.
| Row Width | Length of a single row to equal 1/1000th of an acre |
|---|---|
| 6 | 87' 1'' |
| 7.5 | 69' 8'' |
| 10 | 52' 3'' |
| 15 | 34' 10'' |
| 20 | 26' 2'' |
| 30 | 17' 5'' |
| 36 | 14' 6'' |
2. Determine the plant population per acre. Count the number of plants for the row feet determined above in 6 to 10 randomly chosen area of the field. Multiply this number by 1000. Average the number of sampling areas.
3. Determine the number of pods per plant. Count the number of pods on 5-10 randomly selected plants within the sample area and average.
4. Determine the pods per acre. Multiply the pod average by the plant population (step 2).
5. Determine the number of seeds per acre. Multiply the number of pods (step 4) by 2.5 seed per pod.
6. Determine pounds of seed per acre. Divide the seeds per acre (step 5) by 3000 seeds per pound. This number can vary from 2500 to 3500. Higher numbers represent smaller seed that are more likely during late-season drought. You may want to obtain a low, medium, and high estimate.
7. Determine the yield estimate. Divide the pounds per acre (step 6) by 60 pounds per bushel.
What can we do? It seems that donations to the Red Cross or other reputable charities are best at the moment. Their big needs are money and fuel. There is no power or gas in many of the affected areas. I also heard a comment that there can be a problem of too many people. There seems to be enough people on the ground now. In some areas, you cannot get in. I also heard that, in contrast to what the media is saying, the government is doing a wonderful job. So unless there are new specific requests, I encourage you to work through the Red Cross and other charities at the present. Still, I'm sure we'll be called on to help in the future with cleanup and rebuilding.
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Sincerely,
David L. Holshouser
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