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Index

• Dear Reader
• Manganese Deficiencies in Soybean
• Troubleshooting the Soybean Crop
• Seedling and Vegetative Soybean Diagnostic Outline
• Upcoming Field Days and Conferences

Dear Reader,

Don't forget to begin bumping up seeding rates for these late-planted fields. In order to get adequate canopy coverage, a higher population will be needed.

July is a good month to do some routine scouting of soybean fields. Many temporary and more permanent problems will appear. Manganese deficiencies are one of them. I really don't know what to expect this year in that regard. Soil pH levels were uncharacteristically high this winter; this was due to the high rainfall and leaching of soluble salts. I imagine that they've remained fairly high through the spring, but should be dropping soon. This drop will lower the probability of a deficiency. I briefly discuss this in the first article. Some diagnostic soil and tissue sampling may reveal some unknowns and I'd encourage it.

I've also included a diagnostic guide that I developed a couple of years ago for this newsletter. I've included it again in this issue to help with some of the problems we may experience. I hope that we don't have to use it extensively, but the weather could cause some yet unforeseen problems.

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Manganese Deficiencies in Soybean

Manganese (Mn) deficiencies are common in Virginia soybeans. These deficiencies are not necessarily due to low Mn levels in the soil. Instead, like many micronutrients (nutrients that are needed by the plant in small amounts), Mn availability to the soybean crop is directly related to soil pH.

When pH levels reach 6.5 or above, Mn deficiencies will likely appear, especially on sandy soils. On some soils, Mn deficiencies will occur on soils with pH levels as low as 6.2. In addition, the saturated soil conditions of 2003 may have caused soil pH levels to remain high. However, upon drying, pH in these soils will fall to normal levels rather quickly.

I should address the saturated soil conditions that have plagued much of Virginia this year. For soil samples collected this past winter, we have observed higher than expected pH. Review of past data indicated that soil pH values are generally lower in the fall than in the spring due to leaching of soluble salts during the winter months. Usually, the pH will drop back to normal levels by summer as the soil dries. However, up until a few weeks ago, our soils have not dried very much.

What does this mean? I imagine that soil pH levels have remained relatively high. Does this mean that Mn deficiencies will be more common in 2003? Unless we continue to receive excessive rainfall, I doubt it. The reason being that pH can drop in just a few weeks once the soil dries and aerobic microbial and chemical activity begins.

On the other hand, in wet areas of fields, the pH could remain high. Does this mean that an application of Mn is needed in those areas of the field? First and foremost, Mn is not the biggest problem here. Lack of oxygen to the roots have slowed growth and caused other problems as well. Therefore, throwing good money after bad will not likely improve the situation to a great extent. Mn will only solve one of the problems and will not alone overcome poor growth conditions. Therefore, I cannot advise widespread spraying of Mn on saturated fields or areas within fields.

Another point needs to be made. If soil tests revealed unexpected high pH (6.0 to 6.2) from samples collected this winter, we in Cooperative Extension suggested that the field should probably be limed anyway. The reason being that the pH would be expected to fall back at least 0.5 units. If you were able to lime these fields, then you may be experiencing pH of greater than 6.2 due to the wet soils. Although the pH could still fall back to normal levels, Mn deficiencies under this situation is more likely.

On the other hand, if you did not lime these fields that tested high in pH, then the soils will likely become more acid and a Mn deficiency is less likely.

The question remains, should I expect Mn deficiencies in 2003? This is a tricky question; one with no definite answer. However, I'll suggest the following guidelines:

• Scout your fields. Mn deficiencies may or not materialize. The only sure way to determine a deficiency is to observe the deficiency symptoms. The characteristic symptom is yellowing between the veins on new leaves. Mn is an immobile nutrient. Therefore, it will not move out of older leaves to the new leaves. Symptoms will appear when the plant can no longer extract sufficient amounts of the nutrient from the soil. Typical symptoms are shown to the on the previous page.
• If Mn deficiencies are suspected due to high pH and no symptoms have yet appeared, you may want to consider taking a tissue sample. This can reveal deficiencies before symptoms appear. I would suggest this especially if lime was recently applied.
• To overcome a deficiency, apply 1/2 lb chelated Mn (elemental basis) or 1 lb inorganic Mn (elemental basis) per acre to foliage upon appearance of symptoms and prior to flowering. More than one application may be required to correct a severe deficiency.
• Note that many Mn products recommend applying lower rates of Mn. However, the label usually states that these are maintenance rates. Once a deficiency occurs, these lower rates will not correct the deficiency and the rates stated above will be needed.
• An alternate method of application can be used. Before a deficiency is evident an on soils that commonly show a deficiency, especially on soils recently limed, a lower rate (~ 1/2 of that shown above) can be combined with another scheduled application. Such an application may include a postemergence herbicide. Be reminded that combinations with glyphosate (Roundup, Touchdown, etc.) will result in reduced weed control of certain weeds. Other herbicides have not shown to interact. This may be a sufficient rate to prevent a deficiency from occurring. But, continue to scout the field and take future corrective measures if deficiencies reappear. Symptoms like that shown on the previous page will still require the full rate. I will remind you that this is a preventative treatment. A deficiency may not occur. Furthermore, these are only maintenance rates and another application will likely be needed if the field is truly deficient.

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Troubleshooting the Soybean Crop

Problems with soybean growth and development will occur every year. Diagnosing these problems can sometimes be a challenge but is always a learning opportunity. Keen observation and close attention to details is imperative. Visual diagnostic aids such as insect, weed, and disease identification or herbicide injury sheets are valuable and can be obtained from various sources. But most important are the questions that are asked. Symptoms do not always follow the textbook and obvious patterns do not always exist, but historical information on the field may give solutions to the problem. Below are some guidelines for diagnosing problems with the soybean crop.

Preliminary Fact Finding. Obtain information on each of the following:

• Cropping History (for at least the two previous growing seasons). What crops were planted? What is the typical rotation? Is this the first year that soybeans were grown in this field? Tillage used? Fertilizer, lime, and chemical applications? Any past problems with this or other crops in this field?
• Soil Information. Find out soil texture and classification. A soil map would be handy. Soil test results (Soil pH and levels for P, K, Ca, and Mg) are valuable. Plant tissue test results (major plus most secondary and minor nutrients) may be needed. What were the fertilizer and liming practices (time, rate, and method of application) for this season?
• Weather. Rainfall amounts, temperature, relative humidity during growing season are valuable. If chemical injury is suspected, then identify rainfall patterns (amounts, dates, light vs. heavy, etc.) and temperatures of soil and air before, during, and after application. What was wind speed and prevailing direction during and after the chemical application?
• Pest Management Information. This includes all herbicide, insecticide, fungicide applications and rates for this and the previous crop(s). Other valuable information includes past soil nematode assay results (species and population levels) and major weed or insect problems.
• Tillage and Other Cultural Practices. What were the planting procedures and equipment used? What was the soybean variety? Is the seed tag available? Saved seed? What was the germination?

The Field Visit.. After obtaining as much information as possible before going to the field, follow the general guidelines listed below:

• Materials and Equipment Needed.
• Notebook, paper, pencil, complaint or diagnostic forms
• Mobile phone
• Camera and accessories. Digital cameras are excellent because images can be quickly emailed to specialists.
• Shovel or spade, pocket knife, trowel, other digging tools
• Soil probe, plastic mixing pail, soil sample boxes or bags
• Plastic bags for plant samples that need preserving, paper bags for plant nutrient analysis samples
• Reference books, product labels, other visual aids
• Penetrometer or other soil compaction measurement device (soil probe, pocket knife, metal surveying flag
• Pocket ruler, yard stick
• Magnifying glass, hand lens
• Windshield / Whole Field Investigation. Before looking at plants in the field, try to get a feel for the problem over the entire field. Are there any patterns or trends to the injury? Check neighbor's fields or other soybean fields on the farm.
• Above-Ground Inspection. Identify the soybean growth stage. Know the types of problems that can be experienced at this stage. Did the problem occur in the past or is it ongoing? All affected plant parts should be identified and noted. Compare symptoms with those found in a trouble-shooting guide. Note the occurrence of, identification, and growth of weeds present.
• Below-Ground Inspection. Check the soil texture, condition, moisture, hardness, etc. Inspect the root system. Dig; never pull the plant to inspect the roots. Pulling will dislodge roots and nodules. Is plant well nodulated? Are roots malformed or injured? Check for compaction.
• Documentation. Record information in writing. This doesn't have to be written up as you are diagnosing the problem, but document the evidence before leaving the site. Use a prepared form (University, industry, or self-developed). Fill it out completely. This may be the only opportunity to gather the evidence, so get all of it on paper.
• Equipment Check. If you suspect that the problem may be related to a piece of equipment such as a planter or sprayer, then it would be wise to look at it. Check the general mechanical condition, settings, and spacing.
• Interaction with the Producer (for agents, consultants, company representatives, etc.) Be courteous and respectful. Approach the situation as a service opportunity to solve a problem. Be positive, but careful in your assessment. Know when you are over your head. Get help when you need it. "I don't know" is response that can gain respect.

Analysis of Data.

• Patterns. Look at any patterns that may be present (i.e., streaks, patterns of emergence, tire tracks, cultivation depth, planting depths, soil types, etc.)
• Look-Alike Symptoms. Many symptoms of nutrient deficiency, nematode damage, and herbicide injury look alike. One may be able to infer from field history information what the symptom can be attributed to. But, in many cases, further laboratory analysis will be needed.
• Interacting Factors / More Than One Problem. In most cases, the problem cannot be attributed to a single factor. Herbicide activity closely follows weather conditions. Nematodes can be more or less severe depending on the weather, soil fertility, or cultural practices. The general soil condition (organic matter, structure, etc.) will affect many other things. Compacted soils will enhance any other problem. Certain soybean varieties are sensitive to particular chemicals or combinations of chemicals.

Drawing a Conclusion. Review the facts and data. Evaluate the data regarding what is normal and abnormal. Eliminate unlikely causes. Validate the likely causes (for instance, streaks in the field are related to spraying, tillage, or planting equipment). Remember, a conclusion may not be able to be drawn in the field, especially if laboratory analysis is needed to confirm your suspicions. However, be prompt with you diagnosis. Solve the problem as soon as possible, so remedial actions can be taken.

Follow Up. If the problem was identified, did corrective actions resolve the problem? Re-visit the field. Gather and read any relevant information such as Extension publications, labels, journal reprints, etc. Forward to appropriate personnel

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Seedling & Vegetative Soybean Diagnostic Outline

Seedling (Emergence to V4)

Plants are dead, dying, or stunted in isolated or widespread areas

• ROOTS
  • Dry lesions on roots and portions of stem below surface.
    • Seed or soil-borne fungi or bacteria (e.g., Fusarium spp., Phytopthora spp., or Rhizoctonia solani)
    • Lesion or Columbia lance nematode
  • Taproot and lower stem rotted and dark in color
    • Charcoal rot
    • Phytopthora rot
  • Secondary roots have stubby, burned-off appearance
    • Nematodes
    • Fertilizer salt burn
    • Dinitroaniline herbicides (i.e., Treflan, Prowl)
• STEMS
  • Stem girdled or fed on at or above soil line
    • Three-cornered alfalfa hopper
    • Cutworms (plant usually cut off)
    • Lesser cornstalk borer
    • High temperatures
    • Rhizoctonia solani
    • Fusarium spp.
  • Stem fed on below the soil line
    • Cutworms
    • Lesser cornstalk borer
  • Stem snaps off at soil line when bent over
    • Three-cornered alfalfa hopper
    • Lesser cornstalk borer
    • Surface-applied dinitroaniline herbicides (i.e., Prowl)
  • Upper part of plant chewed or cut off
    • Wildlife damage
    • Cutworms
• LEAVES
  • Leaves discolored, dead, or dropped
    • Thrips (upper leaf surface has silver color)
    • Spider mites
    • Herbicide damage
    • Nematode damage
  • Leaves wilted or dropped
    • Frost damage
    • Lesser cornstalk borer
    • Three-cornered alfalfa hopper
  • Leaves wilted or dropped; soybean and other plants are dead in a circular pattern - lightning

Plants have spots, damage or discoloration of leaves and/or stems; plants may appear stunted with abnormal growth in isolated or widespread areas.

• LEAVES
  • Leaves are torn: hail
  • Show signs of insect feeding
    • Circular holes: bean leaf beetle
    • Irregular holes: green cloverworm, Mexican bean beetle, grasshoppers, other defoliators
  • Show signs of animal feeding: deer, groundhogs
  • Small brown spots
    • Brown spot disease
    • Bacterial pustule
    • Bacterial blight
    • Downy mildew (gray fungal growth on underside)
  • Top or underside of leaves appear speckled or sandblasted
    • Thrips (silvering of upper leaf surface)
    • Spider mites (yellow mottling present)
  • Leaves speckled or burned
    • Cell-membrane disrupting herbicides (i.e., Basagran, Blazer, Cobra, Reflex, paraquat, etc.)
    • Garden fleahopper
  • Leaves showing yellowing, browning, or necrosis along margins
    • Potassium deficiency
    • Potato leaf hopper (may include cupping)
    • Soybean cyst nematodes
    • Triazine or urea herbicides (i.e., atrazine, Princep, Bladex, Sencor, Lorox, Cotoran) (Symptoms are usually followed by browning and necrosis of entire leaf)
    • Boron toxicity
    • Fertilizer salt burn
  • Yellowing of young leaves between leaf veins
    • Urea and sulfonylurea herbicide damage
    • Manganese deficiency
  • Yellowing of old and young leaves; plants may be stunted
    • Magnesium deficiency
    • Sulfur deficiency
    • Nitrogen deficiency
    • Molybdenum deficiency
    • Drowning or water damage (O2 deficiency)
    • Zinc deficiency
    • Aluminum toxicity
    • Herbicide damage
    • Lesser cornstalk borer
  • Leaves cupped upward
    • Benzoic acid herbicides (i.e., Banvel, Clarity)
    • Potato leafhopper
  • Leaves crinkled or disfigured
    • Chloroacetamide herbicides (Dual, Microtech, Frontier, Axiom)
    • Phenoxy herbicides (2,4-D, 2,4-DB, etc.)
    • Diphenylether herbicides (i.e., Blazer, Reflex, Cobra)
    • Manganese toxicity
    • Boron toxicity
    • Various viruses, including soybean mosaic, bean pod mottle, & peanut mottle virus
• STEMS
  • Stems tunneled into at or near soil line
    • Lesser cornstalk borer (look for attached sand tube)
  • Stem girdled or fed on at or above the soil line
    • Three-cornered alfalfa hopper
    • Cutworms (plant usually cut off)
    • Lesser cornstalk borer
    • High temperatures
    • Rhizoctonia solani
    • Fusarium spp.
  • Stem fed on below soil line
    • Cutworms
    • Lesser cornstalk borer
  • Stem snaps off at soil line when bent over
    • Three-cornered alfalfa hopper
    • Lesser cornstalk borer
    • Surface-applied dinitroaniline herbicides (i.e., Prowl)
  • Upper part of plant chewed or cut off
    • Wildlife damage
    • Cutworms
  • Lower stem swollen and/or cracked
    • Excessive rainfall
    • Phenoxy herbicides (i.e., 2,4-D, etc.)
    • Dinitroaniline herbicides (i.e., Treflan, Prowl)
  • Lower stem discolored
    • Phytopthora rot
    • Rhizoctonia solani
• ROOTS
  • Little or no nodule development
    • Low soil pH
    • Molybdenum deficiency
    • Columbian lance, sting, or cyst nematode
    • Soil compaction
  • Little or no secondary root formation - reniform, sting, lesion, or other nematodes
  • Secondary or lateral roots swollen - dinitroaniline herbicides (i.e., Treflan, Prowl)
  • Proliferation of secondary roots
    • Columbian lance nematode
    • Phenoxy herbicides (2,4-D, 2,4-DB, etc.)
    • Northern root-knot nematode
  • Root galls formed - root-knot nematode
  • Small, yellow, lemon-shaped cysts present on roots - soybean cyst nematode
  • Bottle-brush appearance
    • Imidazolinone herbicide (i.e., Scepter, Pursuit, Cadre, Lightning)
    • Northern root-knot nematode
  • Irregular / L-shaped - Soil compaction

Vegetative Stages (V5-R1)

Plants are wilted or dead

• PLANT BROKEN OFF AT GROUND LEVEL
  • Three-cornered alfalfa leaf hopper
  • Surface applied dinitroaniline herbicide (i.e., Prowl)
  • Lesser cornstalk borer
• DISCOLORED OR WILTED LEAVES
  • Silver to light brown areas along the major veins or over the whole leaf - thrips
  • Yellowing followed by browning and necrosis of leaf margins - triazine herbicide (atrazine, Princep, Bladex, Sencor)
  • Leaves are yellow, may wilt; some plant death
    • Phytopthora rot
    • Nematodes
    • Lesser cornstalk borer
    • Grubs, wireworms, other soil larvae
  • Leaves wilted, dead, or dropped
    • Lesser cornstalk borer
    • Grubs, wireworms, or other soil larvae
    • Lightning
  • Leaves yellow speckled; plant stunted; webbing and/or mites present on underside of leaflets - Spider mites
• STEMS DISCOLORED OR SHOWING FRUITING STRUCTURES
  • Discolored stem, reddish fruiting bodies present - Red crown rot (Cylindrocladium black rot)
  • Lower stem discolored
    • Phytopthora rot
    • Rhizoctonia solani
    • Fusarium spp.

• LEAVES
  • Leaves are torn: hail
  • Show signs of insect feeding
    • Circular holes: bean leaf beetle
    • Irregular holes: green cloverworm, Mexican bean beetle, grasshoppers, other defoliators
  • Show signs of animal feeding: deer, groundhogs
• STEMS
  • Stem girdled or dark ring at soil line with possible adventitious root development
    • Three-cornered alfalfa hopper
    • Surface-applied dinitroaniline herbicides
    • Hail
  • Stem fed on at or below soil line
    • Cutworms
    • Wireworms
    • Lesser cornstalk borer
  • Stem tunneled into at or below soil line - Lesser cornstalk borer
  • Stem snaps off at base when plant is bent or blown over
    • Three-cornered alfalfa hopper
    • Lesser cornstalk borer
    • Surface-applied dinitroaniline herbicide
    • Hail
  • Small sand-covered tube attached to stem at soil line - Lesser cornstalk borer

Plants have spots, discoloration of leaves and/or abnormal stem growth; roots may also show stunted or abnormal growth

• LEAVES SHOWING SPOTS, STREAKS, MOTTLING, OR NECROTIC AREAS
  • Dead spots with raised areas on underside of leaf ­ bacterial pustule
  • Leafspots with light-colored centers and dark margins ­ frogeye leafspot
  • Brown spots and/or yellowing on lower leaves ­ brown spot disease
  • Brown spots on upper leaf surface & gray fungal growth on underside of leaves ­ downy mildew
  • Leaves are speckled or burned; new growth is not affected
    • Membrane-disrupting herbicides
    • Sunburn
    • Air pollution / ozone
• LEAVES YELLOWING
  • Yellowing along leaf margins, followed by browning and necrosis
    • Potassium deficiency
    • Triazine herbicides
  • Narrow yellowing along leaf margins and leaf curling ­ potato leafhopper
  • Interveinal yellowing of young leaves
    • Manganese deficiency
    • Sulfonylurea herbicides
    • Brown stem rot
    • Sudden death syndrome
  • Yellowing of old and young leaves
    • Nitrogen deficiency
    • Sulfur deficiency
    • Molybdenum deficiency
    • O2 deficiency (waterlogged soils)
    • Zinc deficiency
    • Nematodes
    • Magnesium deficiency
  • Scorching of leaves along margins
    • Chlorine toxicity
    • Boron toxicity
• LEAVES CRINKLED OR DISFIGURED
  • Leaves crinkled or disfigured, but not stunted ­ various viruses, including soybean mosaic, bean pod mottle, & peanut mottle virus
  • Leaves crinkled and/or distorted with possible stunting
    • Phenoxy herbicides (i.e., 2,4-D, etc.)
    • Glyphosate (i.e., Roundup, Touchdown, etc.) injury
    • Manganese or boron toxicity
  • Leaves cupped up
    • Benzoic acid herbicides (i.e., Banvel, Clarity)
    • Potato leafhopper
• STUNTED OR ABNORMAL ROOTS
  • Little or no nodule development
    • Nitrogen deficiency
    • Greater than 25-30 lbs of nitrogen applied pre-plant to soil
    • Nematodes
    • Low soil pH
    • Molybdenum deficiency
    • Soil compaction
  • Little or no secondary root development - nematodes
  • Secondary or lateral roots swollen ­ dinitroaniline herbicides (i.e., Treflan, Prowl)
  • Proliferation of secondary roots
    • Root-knot nematodes
    • Phenoxy herbicides (2,4-D, etc.)
  • Root galls formed ­ root-knot nematode
  • Small, yellow, lemon-shaped cysts present ­ soybean cyst nematode
  • Secondary roots show bottle-brush appearance
    • Imidazolinone herbicide (i.e., Scepter, Pursuit, Cadre, Lightning)
    • Root-knot nematodes
  • Irregular or L-shaped roots - compaction
  • Evidence of insect feeding ­ wireworms, white grub

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Upcoming Field Days & Conferences

Soybean Field Day: Eastern Virginia AREC, Warsaw, Aug. 19

Tidewater AREC Field Day: Hare Road Research Farm, Suffolk, Aug. 21.

Virginia Soybean Association Winter Educational Meeting: Williamsburg, Jan. 30, 2004.

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Sincerely,

David L. Holshouser

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