Tissue Testing Soybeans

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Carrie Ortel, Extension Soybean Agronomist, Virginia Tech Tidewater AREC

Mark Reiter, Soils and Nutrient Management Extension Specialist, Virginia Tech Eastern Shore AREC

Joseph Haymaker, Postdoctoral Associate, Virginia Tech Eastern Shore AREC

Many of the full-season soybean fields in Virginia are beginning to flower, which is a great time to start tissue testing if there is a concern for crop nutrition. Tissue testing is an effective way to monitor crop nutrition when done correctly. To get reliable results, choose the correct, uppermost fully expanded soybean leaf during optimal conditions and carefully interpret the results. Tissue testing may begin as early as V4 but is most reliable during flowering and can continue through pod filling.

Step 1: Plan Your Sampling During Good Field Conditions

Time It Right – Field Conditions Matter

Field conditions at sampling time greatly affect the accuracy of tissue tests. Aim to collect samples when plants are actively transpiring, which usually means:

  • Adequate soil moisture (not drought or waterlogged).
  • Moderate temperatures and healthy plant function.

Avoid sampling during:

  • Drought, which can limit nutrient uptake even when nutrients are present in the soil.
  • Saturated soils, which can temporarily inhibit root function.
  • Shortly after foliar nutrient applications—wait at least a week and ensure a rain event has occurred to allow nutrients to be absorbed and leaf surfaces to clear.

Address In-Field Variability

Soybean nutrient levels can vary within a field due to differences in soil texture, drainage, or previous management practices. For meaningful results:

  • Divide fields into management zones based on known variability.
  • Take one composite sample per zone, collecting at least 18 trifoliolate leaves randomly throughout that area (Ortel et al., 2023).

This helps identify localized deficiencies and supports more precise nutrient management.

Step 2: Collect Your Leaf Sample

Choose the Right Plant Part

To get consistent and accurate results, it’s critical to sample the correct, uppermost fully expanded trifoliate leaf, as nutrient concentrations differ between leaves. The uppermost fully expanded trifoliate leaf is typically located on the second, third, or fourth node from the top of the plant (Figure 1, shown below).

Figure 1. Soybean plant at the full flower (R2) growth stage. The uppermost fully developed leaf is shown as the leaf on the third node from the top of this plant.

  • Look for the highest leaf that is dark green, full-sized, and has a coarse texture.
  • Avoid leaves with a velvety feel or are lighter in color than others—these are still developing and can falsely indicate nutrient levels.

Check with your testing lab for specific guidelines. Some labs also recommend sampling the whole plant during vegetative stages or including/excluding the petiole (the stalk attaching the leaf to the stem). Be sure your sampling method agrees with the lab’s interpretation standards.

Collect the Sample Properly

Once you identify the correct leaf, follow these best practices:

  • Collect 18–25 leaves per sample for a good composite.
  • Take samples across a consistent management zone (based on yield history, soil type, or other field characteristics).
  • Place leaves in a paper bag (not plastic) to allow drying and prevent mold.
  • Note the growth stage of the soybean crop.

If your lab uses critical nutrient thresholds without the petiole (e.g., Virginia Tech), remove the petiole before bagging.

Step 3: Interpret Results with Context

Getting accurate lab results is only half the process—understanding them correctly is essential.

  • Use growth-stage-specific critical concentrations when available, such as potassium in soybean (Slaton et al., 2021). These values indicate the threshold below which yield may be affected.
  • If no critical values are available, use sufficiency ranges cautiously—they are less precise and based on broader surveys instead of replicated research.

Also, consider nutrient mobility:

  • Mobile nutrients like nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) can move within the plant and are often relocated from leaves to developing seeds and pods (Bender et al., 2015). Lower concentrations in leaves during reproductive stages may not signal a deficiency.
  • Immobile nutrients like calcium (Ca), sulfur (S), and most micronutrients remain in their original locations and offer more stable indicators.

Although some nutrient deficiencies may not be visually apparent (hidden hunger), only take action with a corrective application of fertilizer if a deficiency occurs. Prophylactic foliar fertilizer applications have not been shown to increase yields (Matcham et al., 2021). When a nutrient deficiency does occur, a corrective application of granular fertilizer should be used to correct macronutrients, while a foliar fertilizer may be used to correct micronutrients.

Take Home Points

  1. Collect a composite sample of at least 18 of the uppermost fully expanded soybean trifoliate leaves from each management zone.
  2. Only collect tissue samples during favorable field conditions and adequate soil moisture.
  3. Consider the plant part collected (petiole included or excluded), growth stage, and nutrient mobility with interpreting results.

For more information please contact Carrie Ortel, Extension Soybean Agronomist, at carrieo@vt.edu.

References

  1. Bender, R. R., Haegele, J. W., & Below, F. E. (2015). Nutrient uptake, partitioning, and remobilization in modern soybean varieties. Agronomy Journal, 107(2), 563–573. https://doi.org/10.2134/agronj14.0435
  2. Matcham, E. G., Vann, R. A., Lindsey, L. E., Gaska, J. M., Lilley, D. T., Ross, W. J., Wright, D. L., Knott, C., Lee, C. D., Moseley, D., Singh, M., Naeve, S., Irby, J. T., Wiebold, W., Kandel, H., Lofton, J., Inman, M., Kleinjan, J., Holshouser, D. L., & Conley, S. P. (2021). Foliar fertilizers rarely increase yield in United States soybean. Agronomy Journal, 113(6), 5246–5253. https://doi.org/10.1002/agj2.20889
  3. Ortel, C. C., Roberts, T. L., Hoegenauer, K. A., Poncet, A. M., Slaton, N. A., & Ross, W. J. (2023). Mapping variability of soybean leaf potassium concentrations to develop a sampling protocol. Agrosystems, Geosciences and Environment, 6(4). https://doi.org/10.1002/agg2.20439
  4. Slaton, N. A., Drescher, G. L., Parvej, R., & Roberts, T. L. (2021). Dynamic critical potassium concentrations in soybean leaves and petioles for monitoring potassium nutrition. Agronomy Journal, 113(6), 5472–5482. https://doi.org/10.1002/agj2.20819

Corn earworm pheromone trap update–June 18, 2025

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More locations across Virginia have been added to the corn earworm moth pheromone trapping network. Thanks to the many Virginia Cooperative Extension Agents and Interns (and others) who are monitoring these traps. Here is the Table (it is a pdf file; you’ll need to zoom in). Reporting Virginia counties now include: Augusta, Caroline, Dinwiddie, Essex, Greensville, Isle of Wight, King George, Lancaster, Northampton, Northumberland, Rockbridge, Rockingham, Southampton, Stafford/King George, Suffolk, Surry, Virginia Beach, and Westmoreland. Some high numbers were reported in Stafford/King George (one trap averaging 25 per night) and Virginia Beach (one trap averaging 17 per night).

Asiatic garden beetle update for June 18, 2025

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The entomology program at the Tidewater AREC has continued to monitor Asiatic garden beetle adults in our black light trap. The population peak in early June 2025 (see Figure) is very similar to what we saw in early June of 2024. Much of our cotton now has enough growth on it that some defoliation can be tolerated–but similar to thrips, I would recommend keeping an eye on anything that has not reached 4-5 true leaves.

Corn earworm pheromone trap update–June 12, 2025

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Thanks to the Virginia Soybean Board and all the participating Agents and others who have allowed us to add more pheromone traps to Virginia’s corn earworm monitoring network. Some locations reported zero’s but others such as Caroline and King George had high captures. Here is the Table along with acknowledgements.

Asiatic garden beetle in Virginia cotton–June 12, 2025 update

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Asiatic garden beetle (AGB) captures in our Sussex, VA black light trap spiked the first week of June, totaling 1,281 adults over a 7-day span. Some severe AGB foliar injury to seedling cotton was reported near Wakefield (image below). We dug up cotton plants and marestail in AGB hotspots, finding adults under each, but we do not have evidence that they feed on cotton roots. For more information, please see our Virginia Cooperative Extension publication, “Asiatic Garden Beetle in Cotton”

Expanded corn earworm pheromone trap monitoring network for Virginia

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With funding support by the Virginia Soybean Board, the Tidewater AREC entomology program (led by Dr. Tim Bryant), along with collaborating Virginia Cooperative Extension Agents and Interns, has expanded our Helicoverpa zea (corn earworm/bollworm) pheromone trap monitoring network. Because corn earworm populations vary across the state, knowledge of local moth flights can better inform growers when to scout fields, use insect thresholds, and make the best management decisions for their crops. Here is the Table Numbers in the table represent variable numbers of days between trap checks (most are 3 or 4 nights).

In Dr. Tom Kuhar’s Advisory from May 28, 2025, he discusses high catches of corn earworm moths in Halifax and Northampton Counties, and in Delaware. We saw high catch numbers from Stafford and Caroline Counties this week. We’ll continue to keep you up to date on corn earworm flights across Virginia and expect many more counties to begin issuing reports.

Acephate resistance update in Virginia Cotton

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On Monday, May 26 the Tidewater AREC entomology team collected tobacco thrips from cotton throughout southeastern Virginia. These populations were sent to the University of Tennessee where they were tested in the lab for susceptibility to acephate, spinetoram (Hemi SC or Radiant), and dicrotophos (Bidrin). Across all the sites, the results were very consistent with;

75-79% mortality with acephate
100% mortality with spinetoram
47-50% mortality with dicrotophos

We would classify this as tobacco thrips having reduced susceptibility to acephate in southeastern Virginia. Acephate resistance was also previously confirmed in northeastern North Carolina, just across the state line. This year we have found a high proportion of flower thrips, which are harder to kill with acephate, and now have confirmed that acephate has reduced efficacy for tobacco thrips. If you still plan to make a foliar thrips application, or are making a second application after a previous acephate application, Hemi SC (spinetoram) should be considered for more effective control. See this previous blog post for more details on the importance of timing your foliar application for maximum economic return.

We’d like to thank Sebe Brown at the University of Tennesee and his team for running the lab tests and the Virginia Cotton Board for sponsoring this research.

Mating Disruption of Diamondback moth – An effective strategy that could reduce insecticide applications on cabbage and broccoli

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Authors: Taylore Sydnor (Ph.D. Student), Alejandro Del-Pozo (Assistant Professor) & Thomas Kuhar (Professor) – Department of Entomology, Virginia Tech

Diamondback moth

Diamondback moth (DBM), Plutella xylostella, is an important pest of brassica crops worldwide including Virginia (Fig. 1). Management of this pest is challenging due to its ability to quickly develop resistance to insecticides. Therefore, integrated pest management (IPM) tactics are strongly desired. Mating disruption has been developed for DBM as an alternative to insecticides.  Mating disruption involves releasing high rates of the mating pheromone into fields confusing and/or desensitizing male moths so that they cannot find female moths and mate and produce damaging larvae on the crops.  The strategy has worked extremely well for tree fruit moth pests, and is currently being researched by our lab in Virginia for DBM. 

Fig. 1. Diamondback moth larva and leaf feeding damage.

Mating Disruption Trials

In the past three years we have tested several mating disruption dispensers and other products in commercial cabbage and broccoli fields in Hillsville and Mechanicsville, Virginia.  Similar research has been conducted in North Carolina and South Carolina by our entomology colleagues.  Virtually all of our trials have resulted in sentinel trap shut down of DBM moth catch in the middles of commercial brassica fields that have had mating disruption pheromones released (via dispensers) as compared with non-mating disruption (control) fields that had significant moth catch in the fields (Fig. 2).  When male moths cannot find females, then there will be little to no DBM larval infestations on the crops.  The Trécé Incorporated dispensers (Fig. 3) used in the aforementioned research are not commercially available yet. 

Fig. 2. Weekly catch of diamondback moths (mean ± SE) in baited sticky traps placed in the centers cabbage fields treated with mating disruption dispensers (n= 6) vs. control
Fig. 3. Trécé Incorporated MESO pheromone dispenser in a cabbage field. Photo credit: Taylore Sydnor.

Although we have tested various dispensers, tablets, and sprayable pheromones, with each demonstrating success for reducing DBM, the only commercial DBM mating disruption product currently available to growers is a sprayable pheromone, Checkmate® DBM-F (Fig. 4). The sprayable product has been around for a while, but not heavily used by commercial growers probably because of the plethora of effective lepidopteran insecticides that have hit the market in the past 25 years.  However, with DBM populations developing resistance to virtually all of the insecticide classes, mating disruption is now a more attractive option for managing this difficult pest. 

Fig. 4. CheckMate DBM-F mating disruption product from Suterra.

In 2024, we tested Checkmate® DBM-F in commercial cabbage in Hillsville, VA (4 treated fields paired with 4 control fields), then later in the fall in 2024 in broccoli in Mechanicsville, VA (1 treated field and 1 control field). 

Fields were sampled from July to August. Growers were encouraged to maintain their spray regimens to maintain homogeneity between field plots. All treatment fields in both locations were treated with Checkmate at a rate of 2 fl oz/acre approximately every 30 days. Three pheromone-baited delta sticky traps were placed equidistant in each field plot to monitor the DBM moth activity and were checked weekly. In Hillsville, we found that Checkmate® DBM-F was not significant in reducing DBM populations when compared to the control fields.  However, during this trial there was a lot of rain, 5.34” over a two-week span, that likely reduced the efficacy of the sprayable pheromone to last in the field. In fairness, the company does recommend re-applying the product after rain events.  See the following blog from Suterra that addresses the different rates and frequencies: https://www.suterra.com/blog/checkmate-dbm-f-flexible-spray-timings-for-diamondback-moth-control

This was not possible given the amount of rain that occurred during that 2-week stretch. We felt a more fair assessment of the product occurred with our test in Mechanicsville, where we found that DBM adult captures were significantly shut down in fields treated with Checkmate® DBM-F when compared to control plots (Fig. 5). Overall, we conclude that Checkmate® DBM-F has the potential to be effective in reducing DBM pest populations when applied at the proper conditions.  Growers need to be mindful of rainfall after application. 

Fig. 5. Weekly catch of diamondback moths (mean ± SE) in baited sticky traps placed in the center of broccoli fields treated with CheckMate DBM-F vs. control.
 

Over the past three years, we have tested several types of mating disruption dispensers and products for DBM, and have consistently achieved sentinel trap shut-down (= effective control) of the pest in cabbage and broccoli fields in Virginia.  We encourage growers to try this innovative strategy for controlling this very difficult pest. Please feel free to contact us if you are interested in trying mating disruption for DBM in Virginia.