Category Archives: Commodity

Manganese Deficiencies in Soybean

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Manganese (Mn) deficiencies are starting to appear.  Such a deficiency is common in Virginia soybean, but 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.  However, some soils with a pH of 6.2 and lower can show deficiencies if soil Mn is low.  Generally, Mn deficiencies are more common on our sandier soils as pH changes more rapidly and sandy soils typically have a lower Mn concentration.

The deficiency will appear interveinal clorosis, usually on the younger leaves first since Mn is not a mobile nutrient.  MnDeficiency0721101059This may distinguish Mn deficiency from magnesium (Mg) deficiency.  Magnesium deficiency symptoms will usually appear on the lower leaves while the upper leaves remain green.  Still, I’ve seen Mn deficiency on the lower to middle leaves.  This usually happens when the field has not been checked in a while and the observer missed the symptoms when they were on the younger leaves.Cyst nematode on roots

Other problems can cause look-alike symptoms similar to Mn deficiencies.  In particular, inter-veinal yellowing is a common symptom of soybean cyst or other nematode damage.  Therefore, it may be prudent to further investigate the problem, especially the root system.

 

Use the following guidelines for Mn applications:

Scout your fields.  Mn deficiencies may or may not materialize.  The only sure way to determine a deficiency is to observe the deficiency symptoms through visual observation or tissue tests.  The characteristic visual symptom is yellowing between the veins on the 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.

Take a tissue sample.  If Mn deficiencies are suspected due to high pH and/or a field history of Mn deficiencies, but no symptoms have yet appeared, you should consider taking a tissue sample.  Tissue samples can reveal deficiencies before symptoms appear (hidden hunger).  We suggest a tissue test if lime, lime stabilized biosolids, or an ash product was recently applied.

Manganese application.  To overcome a deficiency, apply ¾ 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.

Don’t use low rates to correct a 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.

Split Mn application on deficiency-prone soils.  An alternate method of application can be used before a deficiency is evident on soils that commonly show a deficiency, especially on soils that have a high pH (above 6.8 or so).  A lower rate (~ ½ of that listed above) can be combined with another scheduled application, such as a postemergence herbicide or insecticide.  This may be a sufficient rate to prevent a deficiency from occurring.  But, continue to scout the field and take future corrective measures if visual deficiencies appear.  If a visual symptom appears, you need to use 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.

Use EDTA chelated Mn formulations when mixing with glyphosate.  Be reminded that some Mn formulations in combination with glyphosate herbicide (Roundup, Touchdown, many generics, etc.) will result in reduced weed control of certain weeds.  Other herbicides have not shown to interact.  If including Mn with glyphosate, use the EDTA chelated formulation as it has shown not to interact.

Don’t spray if you don’t need it.  Mn can be toxic to soybean.  Spraying greater than recommended rates or spraying as a preventative spray when soil pH is relatively low (5.7-5.9) could lead to toxicity problems

Black flag seen in some Virginia cotton fields

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As you may have heard, reports out of northeastern North Carolina are talking about infestations of plant bugs (Lygus) causing a symptom called “black flag” by feeding on presquare cotton.  This is very rare in US cotton.  This symptom is termed “black flag” due to the death and blackened appearance of the expanding terminal leaves.  The danger is creating “crazy cotton”, which is loss of apical dominance, causing multiple terminals per plant, delayed squaring, or yield loss.  Terminals can be destroyed from only 20 minutes of feeding.

But it is important to remember that given good conditions, cotton can recover later in the season without yield loss.  We did research earlier in Virginia that showed that even this far north, cotton can easily compensate from removal of squares—even up to 20 percent—so this black flag injury may not be as big a threat as you may be thinking it is.

The plant bugs that are causing this problem are from a generation that developed on weeds and is moving through the system.  It is important to keep in mind that plant bug infestations are very erratic. Some fields may be infested, or even some areas within a field—but not every field. We and others have checked a lot of cotton fields in Virginia and are finding just a few with very limited amounts of black flag.

We don’t want to overreact to this and spray all of our cotton just because we have seen this problem in a few plants in one area. If you do see these symptoms you should use a sweep net to see if plant bugs are still present (see recommendations below). Overreacting could certainly help flair other problems as well as waste money if plant bugs are not present at damaging levels.

Management on presquare cotton (borrowed from NCSU)

1.  Use a sweep net to make 25 sweep samples and count the adults.  Realize that bug numbers will be higher in field edges, so move around.  A sample of 25 sweeps per location (one set of 25 “swooshes”) should be adequate.

2.  Where you sweep, look for black flag, wilted leaves, or injured terminals.  If you see this injury, and have plant bugs present, spray if the number of injured terminals is greater than 1 plant in 10 feet of row (borrowed from Mississippi State).  If you do decide to spray, use a neonicotinoid at the highest labeled rate at this point in the season.  They tend to be less effective as the season goes on, but should do the trick, while preserving some beneficials.  Examples include Admire Pro, Belay and Centric. DO NOT use an organophosphate or pyrethroid this early in the season.  These will kill the beneficials and could help flare spider mites and/or aphids. We are seeing some of both in a few fields so the risk of flaring these pests is pretty high—and would be very costly.

3.  Monitor the situation after the spray.  A visit and sweeping 24 hours following the spray should give you a good idea of knockdown.  Since you’ve swept and know the plant bug numbers prespray, another good visit would be 4-5 days later.  See if plant bugs have migrated in again and if the terminal injury is holding steady or increasing.

4.  Once the plants start squaring, you need to use a threshold that incorporates plant bug numbers with square retention measurements.  You can find scouting recommendations and the threshold for squaring cotton in the Virginia Cotton Production Guide, http://www.pubs.ext.vt.edu/AREC/AREC-124/AREC-124.html.

The Virginia Peanut-Cotton Infonet has moved (back)

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InfoNetMap

The Virginia Tech Tidewater AREC (TAREC) maintains the Peanut-Cotton Infonet which provides growers in the region with daily weather data (e.g. temperature, rainfall), peanut leaf spot and Sclerotinia advisories, peanut heat units, cotton degree days, and a frost advisory. Four weather stations located in Suffolk, Capron, Skippers, and Waverly are maintained by the TAREC Plant Pathology program. These weather stations transmit data to a computer at the Tidewater AREC, and the data is used to run fungicide advisory models. Data are available on the Virginia Peanut-Cotton Infonet website (http://webipm.ento.vt.edu/cgi-bin/infonet1.cgi).

The data and information available here include:

Maximum, minimum, and average air temperatures
Average soil temperature at a 4 inch depth
Daily and accumulated (from May 1) peanut heat units
Daily and accumulated (from May 1) cotton degree-days
Daily and total seasonal (from May 1) rainfall
Last effective spray date for peanut leaf spot
Sclerotinia blight risk
Frost advisory (from September 25th to completion of harvest)

In addition to the data provided on the Infonet, current information on peanut diseases in the region and disease management recommendations will be provided here on this blog, so be sure to check back for updates.

The Value of Straw

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Farmers are busy in the fields harvesting barley and wheat. Often, farmers opt to bale the straw themselves or allow custom balers to come in and remove the straw from the land. What is the nutrient value of this straw being removed? Check out this publication to figure out what fertilizer nutrients are being removed to help gauge whether the straw should be baled or not. Straw_Value_17June2015

Late blight found in NC

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Late blight has been confirmed in North Carolina on potato.  Few details are known right now regarding the intensity of this outbreak, but, it is focused around the Elizabeth City, NC area.  Potato and tomato growers, particularly those in the SE part of the Commonwealth should be diligent about scouting their crops and consider protective fungicides.  Please let us know if you have further questions and we will continue to update everyone as we learn more.

 

Soybean Replant Decisions

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Deciding whether or not to replant can be a gut-retching decision.  I readily admit that the choice to leave the present stand or replant is not a simple one.  With the cost of seed and diesel fuel, the profitability of replanting may not seem a good idea.  Low prices make this no more appealing.  In the end, your decision should be one based on the estimated dollar gain from replanting.  This will require a careful evaluation of the soybean stand and an analysis of yield potential of the present and replanted crop.

In general, there is less benefit of replanting if stands are reduced uniformly across the field.  Usually replanting can only be justified where stands have been reduced by half.  However, poor stands usually include gaps in addition to merely a lower plant population.  These gaps must be accounted for.  In addition, one may have a 75-80% stand in parts of the field, while other parts of the field may only have 20-25% of the intended plant population; the decision may be to only replant part of the field.

Remember to take into account the yield loss from delayed planting.  Up until mid-June, there is very little yield loss from delayed planting.  After this, for every day delay in planting yield declines about half a bushel per day.  For instance, if replanting in late-June/early-July (about 2 weeks late), your potential yield will have declined by 7 bushels per acre.

A few more questions must be asked before we can proceed with a step-by-step procedure for estimating the profit of replanting.  When considering a replant, do you leave plants in the field and plant through them?  In many cases, planting through the poor stand is a possibility.  If you’re using rows wide enough to fit a tractor tire comfortably between them, then you can split the rows and plant enough new plants to get the final plant population up to 100 to 120 thousand plants for full-season systems (if re-planting before mid-June) or 180 to 200 thousand plants per acre for double-cropped systems (this may require equipment or tractor tire modifications).

On the other hand, a drill will cut up many healthy plants and make them less productive than the ones that you just replanted.  Also, if the drill has wide gauge wheels, then you can severely damage a significant number of plants (there’s a significant amount of down pressure on those wheels – enough to crush a plant on hard soil).  And a damaged plant can sometimes act more like a weed than a crop.  Recognize that the plants growing in the field are going to be higher yielding that any that emerges after replanting.  If you destroy or injure those plants, you’ve just writing off some profit.  Therefore, I do not suggest planting through the old stand with a drill.

Another issue is that if you decide to replant, do you switch to an earlier maturity group?  There is little need to plant an earlier-maturing variety.  Here are two general rules of thumbs:

April/May Plantings:  A 3-day delay in planting will result in a 1-day delay in planting.  Therefore, if planting 30 days later, the crop will mature 10 days later.

June/July Plantings:  A 5-day delay in planting will result in a 1-day delay in maturity.  Therefore, if planting 15 days later, the crop will mature only about 3 days later.

Most important is to plant a maturity group that would grow as long as possible (therefore producing an adequate canopy for maximum yield) and still mature before the average frost date.  If you’re destroying the old crop and starting over, just make sure that the variety you chose will mature before a frost.  Alternatively, if you are planting into the old crop, you may want to choose a variety about one-third to half a maturity group earlier (depending on planting date differences) so that harvest maturity of both plantings will be more in sync.  For example, if you planted a relative maturity group 5.6 on June 10, then you could choose a relative maturity of 5.2 to 5.4 if replanting on June 25.

Finally, realize that you’ll need a higher plant population when planting late.  Final stand with a double-crop planting should be at least 180 thousand plants per acre.  If replanting in July, increase the seeding rate to insure at least 220 thousand plants per acre.

To estimate the profitability of replanting, follow the guidelines listed below.  Be sure to incorporate plant population and gaps in your calculations.  We’ve found that 2- to 3-foot gaps cause as much or more yield loss that from low plant populations.

  1. Determine the cause of the poor stand.  Was the poor stand the result of poor seed quality, cold wet soils, hot dry soils, planting too deep or shallow, soil crusting, herbicide injury, insect or slug feeding, poor soil to seed contact, or disease infection?  Determine if the cause can be corrected to avoid a similar situation.  If slug or insect feeding or disease is the cause, then you might expect poor stands again.
  2. Estimate the stand and percent stand loss due to gaps.  Pace off the sections of row 20 paces long in at least 6 areas of the field.  Determine (in number of paces) the total length of row lost to 2- to 3-foot gaps.  For drilled soybean, this can be interpreted at 2- to 3-foot diameter gaps.  Then determine the percent of row lost to gaps.  In addition, count and determine average number of plants per foot in sections of row not reduced by gaps.  The simplest method is to count the number of healthy plants (capable of recovery) in a length of row equaling 1/1000 of an acre.  For instance:
  • 36-inch rows = 14.5 feet
  • 30-inch rows = 17.5 feet
  • 20-inch rows = 26 feet
  • 15-inch rows = 35 feet
  • 7.5-inch rows = 70 feet

Then, just multiply your counts by 1,000 to get plants per acre.

Or, use the Tables 1 or 2 to determine remaining plant population.  The “hula hoop” method (Table 2) is valuable with drilled soybean or when rows cannot be distinguished.  This involves placing a circular measuring device such as a hula-hoop on the ground and counting the plants contained within.

Table 1. Plant populations of different row spacing with different plant counts per foot.
Plants/ foot Row Spacing
36 30 24 20 15 7.5
Plant Population (1,000’s/acre)
1 15 17 22 26 35 70
2 29 35 44 52 70 140
3 44 52 65 78 105 210
4 58 70 87 105 139 278
5 73 87 109 131 174 —
6 87 105 131 157 209 —
7 102 122 152 183 244 —
Table 2. Hula-hoop method for determining drilled soybean populations.
No. ofPlants Inside Diameter of Hula Hoop
30” 32” 34” 36” 38”
Plant Population (1,000’s/acre)a
6 53 47 41 37 33
10 89 78 69 62 55
14 124 109 97 86 77
18 160 140 124 111 100
22 196 172 152 136 122
26 231 203 179 160 144
aPlants/acre = no. plants ¸ (3.14 x r2 ¸ 43,560 ft2) where r = radius of hula hoop in feet.

 

  1. Estimate the yield of the poor stand.  Use Tables 3 and 4 to determine percent of yield potential for full-season and double-crop plantings, respectively.  Multiply this percentage by the expected yield. This is the yield to expect from the deficient stand.
    Table 3. Yield response (% of maximum) of full-season soybeans to deficit standsa.
    % Stand lost to gapsb Remaining Plant Pop (1,000’s/A)
    70 105 140
    0 95 97 100
    10 93 96 98
    20 91 93 96
    30 88 90 93
    40 83 86 89
    50 78 81 84
    60 73 75 78
    aSource: Pepper and Wilmot.  Managing Deficit Stands. 1991. Illinois Cooperative Extension Cir. 1317.bGaps of 12 inches or more; 30-inch rows

     

    Table 13.4.  Yield response (% of maximum) of double-crop soybeans to deficit standsa.
    % Standlost to gapsb Remaining Plant Pop (1,000’s/A)
    100 140 180 220
    0 80 88 95 100
    20 71 79 86 91
    40 61 69 76 81
    60 48 57 64 69
    aSource: 2001-2004 experiments, Suffolk, VA.bGaps of 3 feet; 15-inch rows; MG 4 variety
  2. Estimate the yield from replanting.  After mid-June, decrease the expected yields an additional half of a bushel per acre per day delay in planting.  This is the yield to expect from delayed planting.
  3. Determine the gain or loss from replanting.  Subtract the expected yield of the poor stand (step 3) from the yield expected from delayed planting.  This is the gain or loss in bu/A from replanting.  Multiply this number by the expected price ($/bu), using future prices, to obtain gain or loss in $/A.
  4. Estimate the cost of replanting.  Include per acre cost of tillage, herbicide, fuel, seed, and labor.
  5. Determine profitability of replanting.  Subtract your cost of replanting from your estimated gain from replanting.