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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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

Xyway Corn Fungicide Trial

Knox County Xyway Trials

Taking stand counts at our Xyway plot – Great looking field of corn!

 

 

A Special Thanks to Ed & Vicki Piar!!

 

The goal of this study is to determine corn’s response to an at-plant soil application of flutriafol (Xyway™) fungicide. Information from this trial will be used to improve corn disease management recommendations for growers throughout the state.

Vomitoxin Research 2022 – Plot #4

Knox County Vomitoxin Research Station #4 Installed – Thanks to Dr. Pierce Paul and Crew!

A Special Thanks to Braddock Farms – Jim and Susan Braddock!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #3

Knox County Vomitoxin Research Station #3 Installed – Thanks to Dr. Pierce Paul and Crew!

A Special Thanks to Clark Farms – Tom and Nate Clark!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #2

Knox County Vomitoxin Research Station #2 Installed – Thanks to Dr. Pierce Paul and Crew!

 

A Special Thanks to David and Emily Mitchem!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #1

Knox County Vomitoxin Research Station #1 Installed – Thanks to Dr. Pierce Paul and Crew!

 

A Special Thanks to Sassafras Hill Farms – Nate McKee and Skyler Epler!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Early Season Wheat Diseases and Fungicides

By: Dr. Pierce Paul, OSU Extension

The wheat crop in Ohio is now between early boot (Feekes 10, in the south) and approaching Feekes 8 (flag leaf emergence) in northern counties. Cooler-than-usual conditions over the last few weeks have slowed the crop down considerably, but as temperatures increase, the crop will advance through several growth stages over a relatively short period. Cool conditions have also kept foliar diseases in check, but Septoria, and to a lesser extent, powdery mildew are still showing up in some fields. Septoria tritici leaf spot is favored by cool, wet conditions similar to those experienced over the last several weeks. It usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with easily-seen dark-brown to black spots (called pycnidia) in the center. Cool temperatures and high relative humidity are also required for the development of powdery mildew. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. If the variety is susceptible and conditions continue to be favorable, a fungicide application may be warranted to prevent both diseases from reaching the flag leaf before grain-fill.

Septoria tritici leaf spot on wheat – note the black dots (pycnidia) inside the lesion.

Most of the fungicides commonly used on wheat are rated as very good or excellent against Septoria and good or very good against powdery mildew. See the attached chart for fungicide options and efficacy. Remember,

Powdery mildew on wheat leaf – as the name suggests, note the powdery, white pustules.

always read and follow the labels when making an application. For both diseases, a single application between Feekes 8 and Feekes 10 would be sufficient to protect the flag leaf and minimize yield loss. However, applications made at these early growth stages will not provide adequate control of late-season diseases like head scab and Stagonospora glume blotch. So, you should scout fields before making your fungicide application decisions. If powder mildew and Septoria levels are low as the crop approaches heading (Feekes 10.5), you may be better off waiting to treat fields at anthesis (Feekes), as this will help to suppress head scab, which is still the most damaging and important disease of wheat in Ohio, while at the same time provide very good control of Septoria, powdery mildew, and late-season diseases such as Stagonospora and rust.