Soybean Diseases are Showing up in Ohio

by: Horacio Lopez-Nicora, Stephanie Karhoff, OSU Extension

In early August we recommended to start scouting fields for soybean diseases. At that time (two weeks ago), disease incidence across Ohio was very low to moderate. Conducive environmental conditions, however, are turning things around and more fields are developing disease symptoms.

Sudden Death Syndrome (SDS)
We are finding fields in Ohio severely affected by sudden death syndrome (SDS) [Fig.1 and Fig. 2]. SDS is caused by the fungal pathogen Fusarium virguliforme. This species is the most prevalent in the region, however, other Fusarium species can cause SDS. SDS above-ground symptoms can be confused with those produced by a different fungus (Cadophora gregata) that causes brown stem rot (BSR). To distinguish SDS from BSR, symptomatic plants should be dug out and stem cut open longitudinally. SDS-infected plants have white, healthy-looking pith, while BSR-infected plants present brown discoloration of the pith. Moreover, fields with severe SDS symptoms can also have high levels of soybean cyst nematode (SCN). Visit here for more information on SDS.

Figure 1. Soybean field in south Ohio severely affected by sudden death syndrome (SDS) with premature defoliation in the R5/R6 growth stage (A); symptoms begin with interveinal yellowing (chlorosis) of leaf (B); eventually leaf tissue dies and becomes brown but veins remain green (C). The fungus infects the root and produces toxins that are responsible for the above-ground symptoms.

If you have SDS, we encourage you to submit a sample to the Soybean Pathology and Nematology Laboratory in the Department of Plant Pathology at The Ohio State University in Columbus (see address below). We will confirm if it is SDS or BSR; additionally, if it is SDS, we want to determine what Fusarium species is the causal agent. To submit samples, dig out three to five symptomatic plants (including roots), placed them in a plastic bag, and submit them to our lab. Do not hesitate to contact your extension educator or us if you have any questions.

Bacterial Blight, White Mold, and Phytophthora Root and Stem Rot

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More on Tar Spot: Mid to Late R-Stage Fungicide Application

Most of the corn across the state of Ohio is now between the late-R1 (silking) and late-R3 (milk) growth stages, with a few late-planted fields at late vegetative stages. Concerns about tar spot, but more likely, a sense of security provided by relatively high grain prices have led to several fields being sprayed with a fungicide at or shortly after R1 and questions being asked about spraying additional fields that are now at mid reproductive stages (between late-R2 [kernel blister] and R3 [milk]) of development. Concerns about tar spot are understandable, given how widespread the disease was last year (2021) and the level of damage it is capable of causing. However, the basic approach for tar spot management in Ohio should be no different from the approach commonly recommended for managing other, more common foliar, fungal diseases such as gray leaf spot. You have to scout fields, monitor the weather, and if needed, apply the fungicide when it is most likely to be effective, without violating label restrictions.

So far this season, of the more than 15 samples examined (actual leaves or images) and 40+ field scouted at 15-day intervals, only three were positive for tar spot. This is considerably lower than what we saw at a similar time and growth stage in 2021. Does this mean that your R2-R3 corn is no longer at risk for tar spot? In places where the disease is endemic (hot spots where lots of spores may be readily available), a susceptible hybrid is planted, and weather conditions are favorable (moderate temperatures and wet and humid), tar spot may still develop and spread quickly after R3. However, under conditions less favorable for tar spot development (cool and dry) where spores need to blow in from outside, the crop is at lower risk for tar spot, even if symptoms begin to develop at R3. So, the short answer is, if you planted a susceptible hybrid no-till or minimum-till in a corn field that had tar spot last year, and weather conditions become highly favorable over the next few weeks, your crop could still be at risk.

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Hail Damage to a Maturing Corn Crop

Hail damage occurred in a few Knox County fields after this past weekend’s (August 20 & 21) round of storms.  Some of you  have asked about the damage potential caused by these storms.

The following information can be found in Evaluating Hail Damage to Corn from the University of Nebraska.  https://extensionpublications.unl.edu/assets/pdf/ec126.pdf

Yield losses can occur from stand reduction, defoliation, and direct damage to the ear itself.  The fields I looked at were in the soft dough to “very” early dent stages.  Table III below shows the anticipated damage due to defoliation.

Table III. Estimated percent corn yield loss due to defoliation occurring at various stages of growth.”

Reprinted from the Com Loss Adjustment Standards Handbook FCIE-2508 (11-2009) 2010 and Succeeding Crop Years, National Crop Insurance Services. This system counts a leaf as fully developed when the leaf tip points to the ground (not fully developed collar).

To estimate total yield loss, consider the following example:

An early August hail storm strikes corn at the soft dough stage. There is defoliation and severe bruising of the ears. The defoliation is calculated at 90 percent.

  1. Ten ears are stripped of their husks and the row number and kernels/row are counted. There are approximately 300 kernels per ear, and on average 30 of these are bruised. This 10 percent direct damage is subtracted from 100 percent, as in the first example with stand reduction.
  2. Defoliation yield reduction ( Table III) for the remaining 90 percent at soft dough is 35 percent.
  3. To calculate yield loss at this point the 10 percent from direct damage is subtracted ( 100 – 10 = 90 percent). The remaining 90 percent is multiplied by 35 percent (90 x 0.35 percent loss). The result is 31.5 percent defoliation loss. The total loss would be from direct damage (10 percent) and defoliation loss (31.5 percent) for a total of 41.5 percent.

This is only an estimate of the percent yield loss. As with undamaged corn, extremely favorable weather during the rest of the growing season can cause actual yields to be higher than expected. Likewise, unfavorable weather can cause greater than anticipated reductions.

Tar Spot Of Corn: What To Know And New Research

by: Dan Quinn and Darcy Telenko, Purdue University

Due to its relatively recent U.S. discovery and its ability to cause significant production and economic losses, tar spot is often a topic of angst and anxiety amongst corn farmers and agronomists in Indiana. For example, a severely infected field can reach yield losses upwards of 60 bushels per acre! Yield losses are often a result of reduced photosynthetic capacity (green leaf area) of the corn plant during grain fill resulting in poor grain fill, kernel abortion, and reduced kernel weight. In addition, severe infection can reduce corn stalk integrity and cause significant lodging later in the season. Tar spot was first confirmed in northwest Indiana in 2015 and the first significant yield-reducing event of the disease was observed in 2018. Similarly, severe outbreaks and large areas of infection of this disease were observed in Indiana in 2021. Tar spot is caused by the fungus known as Phyllachora maydis and can be identified by small, raised black and circular spots present on corn leaves, stalks, and husks (Figure 1). These black and circular spots are known as fungal fruiting structures called stromata, each of which can produce thousands of spores. Overall, tar spot infection and severity can vary based on environmental conditions, the total amount of the pathogen present in the field, and corn hybrid chosen.

What Conditions Cause Tar Spot? Continue reading

Supplemental Forages to Plant in July After Wheat

by: Dr. Mark Sulc, Dr. Bill Weiss, OSU Extension

Some producers may be considering planting a supplemental forage crop after winter wheat grain harvest for various reasons. Some areas of the state are becoming very dry. In many areas, the wet weather this spring resulted in ample forage supply, but good to high-quality forage is in short supply because of the wet weather that delayed harvesting until the crop was mature, or it resulted in rained-on hay that lowered quality.

The table below summarizes options for planting annual forages after wheat harvest.

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Double Crop Soybean Management Considerations

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Wheat harvest is just around the corner, and it’s time to consider double-crop soybean production management. For double-crop soybean to be successful, you need adequate time and moisture for the production of the soybean crop. In southern Ohio, double-crop soybean after wheat harvest is common. In central and northern Ohio, double-crop soybean after winter wheat depends on the wheat harvest date and soybean prices. With high soybean prices, we anticipate interest in double-crop soybean production in central and northern Ohio this year.

Double-crop soybean management considerations.

  1. Soybean relative maturity. Relative maturity (RM) has little effect on yield when soybeans are planted during the first three weeks of May. However, the effect of RM can be larger for late plantings. When planting soybean late, the latest maturing variety that will reach physiological maturity before the first killing frost is recommended. This is to allow the soybean plants to grow vegetatively as long as possible to produce nodes where pods can form before vegetative growth is slowed due to flowering and pod formation.

Table 1. Recommended relative maturity (RM) ranges for soybean varieties planted in June and July in northern, central, and southern Ohio.

  1. Row spacing. Double-crop soybeans should be produced in narrow rows- 7.5 or 15-inch row spacing. The later soybeans are planted, the greater the yield increase due to narrow rows. Soybeans grown in narrow rows produce more grain because they capture more sunlight energy, which drives photosynthesis.
  1. Seeding rate. The soybean plant population at harvest for mid-to-late June plantings should be between 130,000-150,000 plants/acre. The harvest population for early July plantings should be greater than 180,000 plants/acre. Harvest population is a function of seeding rate, quality of the planter operation, and seed germination percentage and depends on such things as soil moisture condition, seed-soil contact, and disease pressure.

Double-Crop Soybean Weed Management

by: Dr. Mark Loux, OSU Extension

It’s been a tough summer in parts of Ohio to do anything on a timely schedule and there are some weedy fields.  The best advice we have for big weeds in full-season soybeans is to increase rates and the complexity of POST herbicide applications, while still adhering to cutoffs for the application of certain herbicides as much as possible.  Dicamba products, XtendiMax, Engenia, and Tavium, cannot legally be applied to Xtend and XtendiFlex soybeans after June 30.  This cutoff date pertains to use in double-crop soybeans also.  If you are planning on planting Xtend or XtendiFlex soybeans in double-crop fields and using dicamba as a burndown, apply before Friday.  There isn’t a cutoff date for most other POST soybean herbicides – it’s based on either crop stage (eg R1) or days before harvest.

Double crop soybeans usually need some type of weed control program, although how weedy they get depends upon weeds surviving down in the wheat that can take off once they receive light; how much rain we get in July, which drives additional weed emergence and rate of soybean growth; and how fast the soybeans grow and develop a canopy.  Control can occur via the use of pre-plant/preemergence burndown herbicides, followed by POST as needed.  It’s also possible to accomplish this with one early POST application in Enlist soybeans, using Enlist Duo or a combination of Enlist One with glyphosate or glufosinate.  And also in LLGT27 soybeans with a combination of glyphosate and glufosinate.  Herbicides need to address marestail in many fields, which is often lurking in the wheat ready to regrow.  Marestail that are taller and get cut off by the combine will be more difficult to control than the smaller intact ones below the cutter bar.  Herbicide options vary depending upon the weeds and what type of soybeans are planted.  More effective options include:

  • Glyphosate or glufosinate + Sharpen (1 oz) + MSO – any soybean, prior to emergence
  • Glyphosate or glufosinate + 2,4-D – any soybean, at least a week before planting
  • Enlist Duo; glyphosate or glufosinate + Enlist One (Enlist soybeans) – PRE or POST, no wait to plant
  • Glyphosate + XtendiMax or Engenia (Xtend or XtendiFlex soybeans) – PRE, apply by June 30
  • Glyphosate + glufosinate – PRE in any soybean, PRE or POST in LLGT27 soybean

​​​​​​​It is possible to include residual herbicides with a PRE burndown treatment, but their value in this situation is questionable.  Residual herbicides with long recrop intervals to corn should be avoided.  POST options in double-crop include glufosinate, glyphosate, Enlist One/Duo, and conventional herbicides, depending upon the type of soybean planted.  One caution here is to avoid excessive injury to soybeans that slows growth and development since this is likely to reduce yield due to the short season.  Weed emergence is reduced and variable in July compared with May and June.  Where burndown herbicides are used, but there is still a need for POST herbicides to control a flush of late-emerging weeds, consider reduced rates.  Research we conducted back in the 1990s demonstrated that weeds up to 2 inches tall can usually be controlled with half of a typical labeled rate.  When we planted soybeans in early June, the single application of a half-rate provided adequate control, versus early May when a second application was needed.  So this should be a suitable approach for double-crop soybeans.  Just be sure to start with an effective burndown at planting, and apply when weeds are well within the 2-inch size.

Ohio Department of Agriculture Reminds Pesticide Applicators of June 30 Cutoff Date for Dicamba Products

The Ohio Department of Agriculture (ODA) is reminding pesticide applicators of the June 30 cutoff date for over-the-top dicamba products to soybeans. No additional applications can be made to this year’s crop after this date, regardless of growth stage.

Dicamba is an herbicide used to help limit unwanted weeds around crops. In 2018, the Environmental Protection Agency (EPA) designated new dicamba products as restricted use, meaning they can only be used by certified applicators.

In December 2021, the EPA released its 2021 incident report, which indicated that across the United States “more than 1 million acres of non-dicamba-tolerant soybean crops were allegedly damaged by off-target movement of dicamba.” In Ohio, there were 34 reported incidents involving dicamba.

If you have questions or concerns about dicamba please contact the Division of Plant Health’s Pesticide & Fertilizer Regulation Program at (614) 728-6987 or Pesticides@agri.ohio.gov.