Figure 1. Foliar Symptoms

Red crown rot (RCR) is a soybean disease caused by the soilborne fungus Calonectria ilicicola that is spreading to parts of the Midwest. There have been no confirmed reports of RCR in Ohio, but it has been detected in Kentucky and Illinois.  RCR can be easily confused with other soybean diseases that cause similar foliar symptoms.

RCR can be misidentified as sudden death syndrome (SDS) or brown stem rot (BSR) as all three diseases can cause yellowing between the leaf veins or interveinal leaf chlorosis (Figure 1.)

Figure 2. Stem discoloration

Proper diagnosis will require digging up the plant, scraping the soil off, and inspecting for red discoloration on the outer stem (Figure 2). Also look for small, brick red perithecia (fungal sexual structure) on the lower stem or root crown area. These perithecia will be smaller than the tip of a pencil and more likely to be observed following wet weather.

In general, concentrate scouting efforts for RCR in low-lying, saturated areas of the field between the R3 (beginning pod) and R5 (beginning seed) growth stages. Keep an eye out for scattered patches of plants dying off early.

If you have questionable areas in your beans and suspect RCR or sudden death let me know.  I can collect plant samples and send them to our lab for diagnosis.

Source: Horacio Lopez-Nicora

Now is the time to scout for mid-season soybean diseases. Though, disease levels across Ohio are low to moderate, current weather conditions are turning things around, and more fields are developing disease symptoms.

Sudden Death Syndrome (SDS)
We are finding fields in Ohio affected by sudden death syndrome (SDS). These symptoms are showing up earlier than normal. 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).

If you are seeing SDS symptoms, 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 (read more HERE). 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, complete the SDS submission form, and submit them to our lab. Do not hesitate to contact your extension educator or us if you have any questions.

White Mold, and Phytophthora Root and Stem Rot
Weather conditions are favorable for development of white mold, a fungal disease caused by Sclerotinia sclerotiorum. To scout for this disease, we recommend walking soybean fields and looking in-between rows. A white fluffy mass of fungal mycelia will be observed in infected plants (Fig. 4). Black round sclerotia will be present amidst the white mycelia. Visit here for more information about scouting for white mold of soybean.

We continue to receive samples with plants affected by Phytophthora root and stem rot. Commonly, these samples come from fields with poor drainage. Phytophthora root and stem rot can sometimes be confused with stem canker and white mold. You are welcome to submit samples to the Soybean Pathology and Nematology Lab for diagnosis. Visit here for more information about scouting for Phytophthora root and stem rot in soybean.

Frogeye Leaf Spot
We are finding frogeye leaf spot in our fungicide trials in northern and southern Ohio. Frogeye leaf spot is caused by a fungal pathogen (Cercospora sojina) which can reduce yield if plants are severely affected between R3 to R5 soybean growth stages. This year, symptoms in Ohio are visible at R2/R3 growth stage. We encourage growers to submit samples with frogeye leaf spot lesions to our lab. The fungus can develop resistance to fungicide, and we want to determine if these populations are present in Ohio. Best way to submit frogeye leaf spot samples to our lab is by placing symptomatic leaves in a plastic Ziploc bag and mail it to our lab as soon as possible. Keep samples in cool conditions and avoid exposure to sunlight and heat. Visit here for more information on frogeye leaf spot.

We can help diagnose soybean diseases with you!
You are welcome to submit your samples to the address below. Contact us if you have any questions. Send your samples to:

Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu

Source: Horacio Lopez-Nicora

We are finding fields in Ohio affected by sudden death syndrome (SDS). These symptoms are showing up earlier than normal. 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.

With support and funding from Ohio Soybean Council, we will process soybean plants with SDS symptoms from fields in Ohio to: 1) Determine the species and genetic diversity of Fusarium associated with SDS in Ohio, and 2) Determine the fungicide sensitivity of isolates in the culture collection. To successfully achieve these goals, we need your help.

If you are seeing SDS symptoms, 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 (read more HERE). 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, complete the SDS submission form, and submit them to our lab. Do not hesitate to contact your extension educator or us if you have any questions. Read more about SDS and other mid-season diseases of soybean HERE.

Mail your samples to:

OSU Soybean Pathology and Nematology Lab 
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu

Read more about SDS here

Sudden death syndrome (SDS) of soybean can be found in fields around the Midwest but still has limited distribution in Ohio. Yield losses associated with SDS in Ohio have been highly variable depending on the timing and severity of the initial infection, subsequent weather conditions, timing of defoliation, and the level of soybean cyst nematode (SCN) infestation in the field.

Symptoms and Signs – Foliar:

The first observed SDS symptoms are often early leaf symptoms, including yellow spots between leaf veins, known as interveinal chlorosis.

These lesions may expand and turn brown as the spots expand between veins, which is called interveinal necrosis. Leaf veins remain green. As the disease progresses, leaves die and prematurely fall from the plant, while petioles remain attached to the stem. Pods and seeds may be aborted.

Foliar symptoms of SDS can resemble those of many other diseases. These symptoms can occur in fields with high levels of inoculum as early as the vegetative stage, but most often occur near the middle pod-fill stages (R3-R4).

Symptoms and Signs – Roots & Stems:

Infected plants can have discolored and decaying roots even if there are no noticeable foliar symptoms of SDS. The woody tissue in the taproot can be brown to dark gray, while the upper portion of stem pith remains white.

Disease Cycle:

Click here to enlarge

The fungus that causes SDS survives the winter in crop residue and soil. Early in the season, the fungus infects soybean roots, sometimes within a few days of seed germination. Infection is favored by cool, wet soil conditions. The SDS fungus produces toxins that plants transport through their water-conducting vessels (xylem) up to the leaves, which results in foliar symptoms. Typically, these symptoms occur after flowering, but they have been observed during early soybean growth stages on highly susceptible varieties or when conditions are favorable.

Conditions that Favor Disease: Cool, wet field conditions shortly after planting favor early root infections and disease establishment. Frequent or heavy rains midseason can favor early symptoms.  Hot and/or dry conditions in the spring or summer can halt SDS development.

The presence of soybean cyst nematode (SCN) in the same field where SDS is found can increase the severity of SDS symptoms. Therefore, fields with SDS should be tested for the presence of SCN. Research has linked the presence of SCN with higher levels of SDS and increased yield loss. However, SDS can occur independently of SCN, and vice versa. Some crop production practices may also increase the risk of disease development. Fields with poor soil nutrients, low pH, poor drainage, or moderate to severe soil compaction are at higher risk of SDS.

Yield Loss and Impact: Yield losses due to SDS can be highly variable and depend on several factors, including the environment, the timing of symptom development, the susceptibility of a soybean variety to the disease, and the levels of SCN present in the field. SDS can weaken plants and cause premature defoliation — infected plants also may produce fewer and smaller seeds.

Yield losses can be substantial in years when susceptible soybean varieties are planted in cool, wet fields with a history of SDS and SCN. If symptoms develop later in the season, or weather is not conducive for disease development, yield losses can be minimal. Losses are rarely fieldwide since the disease often occurs in patches.  If foliar symptoms appear at or after growth stage R6, yield loss may be minimal.

Management: SDS management strategies include planting soybean varieties with SDS resistance, managing SCN, using effective fungicide seed treatments, improving soil drainage in fields with recurring SDS, rotating crops, avoiding or reducing soil compaction, and maintaining proper pH and fertility levels.