Michigan Soybean On-Farm Research In-Season Management Guide

Summer 2023

michigan

soybean on-Farm Research in-season

management guide

The information in this publication is the result of checkoff investments in soybean research. We hope you find this information valuable and wish you a successful 2023 soybean crop.

Table of contents

Identifying & Responding to Poor Nodulation in Soybeans

Equipping & Operating Sprayers to Control Insects & Diseases in Soybeans

Identifying and Correcting Nutrient Deficiencies in Soybeans

Gall Midge Moves Slowly, but Surely, East

From our Research Director

“The more things change, the more they stay the same”. This publication is a good example of the need to continue identifying ways to reduce yield losses in soybean production. In it, you’ll find information from expert researchers on nutrients, nodulation and sprayer operation to optimize crop yields and profit. It also provides an introduction to a new insect pest to the U.S. - the Soybean Gall Midge.

A few other examples of new areas of research this year include the evaluation of deer predation on soybeans, biological seed treatments, biostimulants, soybean microbiomes and planter technologies. While our goal to improve the production, profitability and sustainability of Michigan soybeans remains the same, we are broadening our research focus to address issues that are becoming more prevalent on Michigan farms.

As always, please share your input with us as we strive to create the highest return and value for your checkoff investment.

From our Research subcommittee

We have frequent discussions as a board about ways we can make sure that the projects we fund are relevant and timely. As a research subcommittee, we diligently review each proposal to make sure that it has the potential to benefit Michigan soybean farmers and is practical and well thought out. We hope you see value in the investments MSC makes in research, and are able to utilize the results to benefit your operation.

I would encourage you to share any research trial ideas and consider participating in an on-farm trial yourself. It’s a great way to learn firsthand if the ideas are a good fit for your farm.

identifying and responding to poor nodulation in soybeans

MIKE STATON MSU EXTENSION SOYBEAN EDUCATOR

symptoms. Inoculation failures are most likely to occur in first-year soybeans or when soybeans are planted following forage legumes or manure applications. Stress from saturated soils, dry soils and very high temperatures can also cause poor or failed nodulation.

If you see short and light green soybean plants in late June or early July, you should suspect poor nodulation. The best way to identify the problem is to dig up plants in the affected areas, wash the roots carefully and count the root nodules. If fewer than seven nodules are found per plant, the plants will probably be nitrogen deficient. Only nodules that are two millimeters or larger and pink or red when split open, should be counted. Dysfunctional nodules will most likely be white, green or brown. White nodules are immature and have not begun fixing nitrogen. Green nodules are mature but no longer fixing nitrogen and brown, mushy nodules are usually caused by saturated soil conditions lasting at least five to seven days.

Timely applications of 60 to 80 pounds of actual nitrogen per acre to soybean plants showing nitrogen deficiency symptoms and having few or no nodules can increase yields by up to 10 bushels per acre. Ideally, the supplemental nitrogen should be applied between the R1 growth stage (one open flower on 50% of the plants) and the R2 growth stage (one open flower on one of the upper two nodes on the main stem on 50% of the plants). However, Kansas State University has reported positive results when nitrogen was applied to nitrogen deficient plants at R3 (one pod 3/16 of an inch long on one of the upper four nodes on the main stem on 50% of the plants) if rainfall or irrigation occurs soon after application.

28% urea-ammonium solution (28% UAN) is the preferred nitrogen fertilizer for this application. One reason is half of the nitrogen is immediately available to the plants. Another reason is the fertilizer is applied using sprayers having wide booms and narrow tires, reducing the potential for tire damage to the plants. Broadcast applications of 28% UAN will burn the leaves, so the fertilizer must be applied to the soil using drop tubes or hoses. Urea can be broadcast without burning the leaves if the foliage is dry. However, more tire traffic damage will occur when applying urea due to the narrower spreading pattern and wider width of the tires on the spreaders.

Other downsides of applying urea are that the nitrogen is not immediately available and is in a form subject to volatilization losses under hot, dry conditions.

Soybean root nodules

Equipping and Operating Sprayers to Control Insects and Diseases in Soybeans

MIKE STATON SOYBEAN EDUCATOR MICHIGAN STATE UNIVERSITY EXTENSION

Controlling insects and diseases in soybeans can be challenging because they commonly start in lower, hard-to-reach parts of the canopy. For example, soybean flower petals are the primary colonization sites for Sclerotinia Stem Rot (white mold) spores. To effectively manage this disease, fungicides must be directed at soybean flower petals, especially in the lower parts of the crop canopy. Flower petals are very close to the stem of the plant and at about two-thirds of the height of the plant from the ground up. This article will help you maximize insect and disease control in soybeans by equipping and operating your sprayer properly.

Spray volume has the greatest impact on canopy penetration and leaf and stem coverage. Spray volumes of 15 gallons per acre are required when applying insecticide and fungicides to soybeans through growth stage R3 (pod development). After R3, 20 gallons per acre will improve coverage.

Droplet size is the second most important factor affecting canopy penetration and coverage. Research has shown that under thick and tall canopy conditions, fine to medium droplets having Volume Median Diameters (VMDs) ranging from 200 to 350 microns provide better leaf and stem coverage and canopy penetration. All nozzle manufacturers, following a Standard developed by ASABE (American Society of Biological and Agricultural Engineers), use a common spray quality classification system shown in Table 1. Each droplet size class is also identified with a unique and internationally accepted color. For example, yellow is the color for droplets falling in the medium (M) category. The colors listed in Table 1 should not be confused with the color of the nozzle itself. The colors listed in Table 1 refer to the droplet size range and the color of the nozzle refers to the flow rate, commonly referred to as capacity.

Ground speed is an important consideration as it affects the spray application rate

(gallons per acre or GPA) significantly. There is a direct but inverse relationship between the travel speed and the application rate. For example, if the travel speed is doubled, the application rate will be halved and vice/versa. In addition, higher travel speeds generally increase the drift potential and reduce canopy penetration. Ground speeds of less than 10 mph are recommended.

Nozzle pressure must be considered when equipping and operating sprayers. Higher spray pressures increase GPA and droplet velocity, but decrease droplet size, increasing the risk of spray drift and droplet evaporation. These concepts are shown in Table 2. In general, spray pressures of 40 psi are recommended for conventional flat-fan nozzles. Higher pressures are okay if the optimum droplet size spectra is produced.

Nozzle type and spray pattern are important factors. Research conducted at the Ohio State University showed that nozzles producing a single flat-fan pattern

Table 1. ASABE standard 572.3 (spray quality categories)

DR. ERDAL OZKAN PESTICIDE APPLICATION TECHNOLOGY SPECIALIST OHIO STATE UNIVERSITY EXTENSION

provided better canopy penetration than nozzles or combinations of nozzles producing a twin-fan pattern or cone nozzles when used in large and dense soybean canopies. Because they produce relatively larger droplets, venturi or airinduction nozzles are not generally recommended for insecticide and fungicide applications.

Table

Consider spray volume, droplet size, ground speed and operating pressure when selecting spray nozzles. Select nozzles that produce droplet sizes near the fine end of the medium (yellow) category and deliver 15 gallons per acre at your desired ground speed and operating pressure. The information in Table 2 shows that a sprayer, equipped with XR11005 nozzles, operated at 40 psi, and traveling at 10 mph will deliver 14.9 GPA while producing droplets near the fine end of the medium category. Note that the color of the XR11005 nozzle is brown and it produces droplets in the medium (yellow) to fine (orange) categories depending on the operating pressure. Table 2 also shows that XR8004 and XR11004 nozzles are viable options if the ground speed is reduced to 8 mph. All nozzle manufacturers provide similar information for each of their nozzles.

*C: coarse, M: medium, F: fine

Boom height has a significant influence on spray pattern uniformity. The boom height recommended by nozzle manufacturers is the distance between the target and the nozzles on the boom that achieves the most uniform spray pattern at the target area. When spraying soybeans for white mold, the target area should be where the flower petals are (top 1/3 of the canopy). Therefore, the boom height should be measured from this area up, not from the top of the canopy or from the ground. For example, a boom equipped with 110 degree flat-fan nozzles spaced 20 inches apart should be operated 16 to 18 inches above the target area. When setting the boom height for treating white mold,

the boom would be 10 to 12 inches above the top of the canopy in 24-inch-tall soybeans. However, if the soybean canopy is extremely tall and dense, the target area should be about 5 inches below the top of the canopy and the boom would be 11 to 13 inches above the top of the canopy to avoid streaks of totally untreated areas.

The recommendations discussed above will improve insect and disease control in large, dense soybean canopies.

Key Takeaways:

• Use volume of 15-20 gallons per acre

• Select medium to fine droplet size

• Keep ground speed at 10 mph or less

• Aim for 40 psi with a flat fan nozzle

Source: Catalog 52, Spraying Systems Co.

2. Relationship between spray volume, ground speed, pressure and droplet size for Teejet XR8004, XR8005 and XR11005 nozzles (nozzle spacing is 20 inches)

in-season nutrient management considerations

DR. KURT STEINKE

MSU ASSOCIATE PROFESSOR, SOIL FERTILITY AND NUTRIENT MANAGEMENT

Now that the 2023 planting season and the hot, cold, wet and dry conditions of yet another typical Michigan spring are behind us, our attention turns to mid- to latesummer soybean growth and development. While I often use the term “frustrating” to describe soybean yield in response to nutrient applications at above-critical soil test values, the same terminology may also apply to inseason nutrient management. There are however some considerations to think about heading into the latter half of the growing season.

Is a nutrient deficiency showing from actual lack of a nutrient or related to weather conditions? Remember plants do not grow to water, they grow through water. Whether a nutrient moves via mass flow or diffusion, reductions in soil moisture decrease water transport and diffusion pathways, reducing nutrient uptake. Due to this, nutrient deficiency symptoms may be visible even when soil test levels are above the critical level under dry soil conditions.

Soybeans remove more potassium per bushel than corn. A 60 bu/A soybean crop removes about 70 lb K2O/A as compared to 40 lb K2O/A in a 200 bu/A corn crop. The key point to remember with soybeans however is that K uptake occurs much earlier in the season than other nutrients with about 25% of K uptake complete by R1 and 70% by R4 (seed-fill). Unlike some of the other macronutrients, much of the K uptake after seed-fill is remobilized from the plant and not taken up from the soil, further demonstrating the importance of pre-plant soil test K concentrations (> 100 ppm for CEC < 5; > 120 ppm for CEC >5) for maintaining tissue K concentrations later in the season. Due to the large quantity of K that soybeans uptake, foliar applications struggle to provide sufficient K. Soil-applied K applications (i.e., drop-nozzles, Y-drops, etc.) have been investigated on many occasions with rarely significant results and are not recommended or suggested. If a producer wants to make an in-season K fertilizer application to the soil, be sure to use a soluble K source, focus on known high-yielding areas and apply near rainfall or irrigation prior to the R1 growth stage.

Manganese (Mn) remains the most common soybean micronutrient deficiency in Michigan with both dry soil conditions and high soil pH (> 6.5) contributing to visible deficiency symptoms. Soybeans will respond to Mn applications when deficient. Typically foliar applications of 1-2 lbs. Mn/A will correct the deficiency, but growers should note which areas of the field develop Mn deficiency as symptoms are likely to reoccur when Mn-sensitive crops are grown.

Despite the ability to fix a substantial percentage (44-72%) of N from the

atmosphere and access the remainder via soil N mineralization, residual soil N, or atmospheric deposition, questions persist about soybean N applications. Unlike potassium, soybean N uptake is only about 20% and 50% complete at R1 and R4, respectively. Hence almost 50% of N uptake occurs late in the season with a sizable percentage of this coming from the soil. The time-frame for late-season N uptake, however, also coincides with peak N availability via soil mineralization, which when combined with biological fixation often provides sufficient N for soybean yield. Have soybean responses to N application occurred? Yes. Should a soybean response to N application be expected? Not likely. Thus N applications to soybean are not recommended unless nodulation failure has been documented. If a grower wishes to attempt an in-season N application, growers should focus on season-long N availability, shy away from soluble pre-R1 N applications, and remain in the 50-80 lbs. N/A range. High-yielding (> 70 bu/A) field areas with sandy soils and minimal organic matter accumulation may be the most responsive to N application but again should not be expected. Starter fertilizers at rates < 25 lb N/A have shown consistent biomass response with negligible impact on N fixation but inconsistent yield responses have often followed. Be careful not to assume that a larger soybean canopy will result in greater yield. Excessive soybean canopy development can result in too much water usage, white mold occurrence, and plant lodging creating difficulties with pod set and grain fill.

Y-drop applicator applying in-season fertilizer to the soil near the base of the soybean plant.

Mn deficiency symptoms

GALL MIDGE MOVES SLOWLY, BUT SURELY, EAST

DR. CHRIS DIFONZO MSU PROFESSOR & FIELD CROPS ENTOMOLOGIST

One of the most frustrating soybean pests to emerge this century is the soybean gall midge. After 100+ years of large-scale corn and soybean production in the U.S., most new pests are species introduced from abroad, for example the soybean aphid and brown marmorated stink bug from Asia. Occasionally, a native pest expands its range; western bean cutworm comes to mind. But it is rare for a localized native insect to suddenly ‘become’ a crop pest. The soybean gall midge apparently did just that. After a few years of scattered reports in soybeans, it had a broader outbreak in several western states in 2018 and has been spreading ever since. A specialist determined that the midge was a new, unknown species existing nowhere else. Much of its origin and biology are still a mystery.

Midge larvae injure soybean plants by feeding on the stems, often near the soil line (A). The feeding not only cuts off water and nutrient movement, but allows pathogens to enter wounds. Besides stem damage, plants can wilt, lodge or die (B). The adult midges are tiny delicate flies which can’t fly very far after they emerge in June, thus infestations usually start on field margins closest to last year’s soybean ground. Egg laying and larval feeding can start in the early V-stages. Yield loss can be high, particularly on field edges (C), but management options are limited so far.

Gall midge is currently reported in 155 counties in the U.S., west of a line roughly from the Twin Cities south to Des Moines, Iowa. This puts it 340 miles due west of Ludington (in Rice County, MN) or the southwest tip of Michigan (in the Des Moines area). To date its spread is slow, moving a few counties to the east each season. But this does not rule out the possibility of farther spread due to weather fronts, or the possibility that low level infestations get missed where people aren’t looking. So when scouting soybean fields in the summer, be aware of what is happening on field edges and be curious if you see wilted or dead plants that aren’t associated with spider mites. It’s unlikely that gall midge would be found in Michigan before detection in Wisconsin or Illinois, but you never know!

The University of Nebraska oversees the Soybean Gall Midge Alert Network, a one-stop-shop for a current distribution map, scouting and management information, plus pictures and videos to aid in scouting and identification. You can also sign up for cell phone alerts of adult and larval emergence in the western states. The network is sponsored in part by the North Central Soybean Research program, and thus your checkoff dollars are at work. Visit https://soybeangallmidge.org to learn more.

Photos from Justin McMechan, University of Nebraska-Lincoln