Thanks for checking out our “Ask the Agronomist” feature! Here, we’re answering some questions we’ve been getting about Sudden Death Syndrome.

Q: We’ve received a question from a farmer this week saying “Sudden Death Syndrome is breaking bad in my soybean fields. Why does it appear to be affecting more fields this year and what can I do about it?”

A: Sudden Death Syndrome appears after flowering in the growing season, and usually we see issues in early August. Cool, wet planting conditions, like what the Upper Midwest experienced earlier this year, can increase severity of sudden death later on in crop development.

Q: What symptoms should we be looking for?

A: Farmers should first be scouting for yellow blotches on leaves. These will progress into larger patches, but keep in mind that leaf veins remain green while the rest of the leaf will eventually turn brown and leaflets will fall off. However, petioles will remain on the stem. SDS can cause rotted root systems, too.

Q: Are there certain soil types or fields more prone to SDS?

A: There isn’t a certain type of soil that is more prone, but there are specific areas of a field that can more easily develop SDS. High moisture areas such as low spots can have higher severity, and it is also often correlated with compacted soils in margins of a field or low-lying bottoms.

Fields with a history of SDS should be planted when soils are warmer and drier. No-till practices allow soils to remain cooler and wetter during the spring, so these fields are more at risk as well. Sometimes, tillage on a field with a history of SDS is a good practice as long as those fields aren’t worked in wet conditions.

Q: What can farmers do if they begin to notice SDS in their fields this year?

A: Unfortunately, there is not much that can be done to stop SDS once it begins. Prevention is the best defense against SDS. Prevention tactics include: responsible tillage practices to reduce soil compaction, waiting for soils to dry up towards the end of planting seasons, and testing for presence of soybean cyst nematodes. Soybean Cyst Nematodes (SCN) are associated with SDS.

Q: What can be done if farmers test their soils and find a soybean cyst nematode presence?

A: The best way to combat SCN is to plant resistant varieties, or avoid susceptible varieties. Be sure to keep Latham IRONCLAD™ soybeans in mind when mapping out which varieties will be used on different fields.

To bear the IRONCLAD™ name, each soybean variety must be SCN resistant, phytophthora root rot resistant, and an iron deficiency chlorosis rating of 2.2 or better. Depending on the geographic location needs, IRONCLAD™ varieties must protect against either white mold or SDS with a rating of 2.2 or higher.

Q: If there is no cure for SDS, why should farmers be scouting for it?

A: An ounce of prevention is worth a pound of cure. Scouting for SDS is important to determine if management practices were at fault and to help select the right seed for each field next year based on SDS score and Soybean Cyst Nematode tolerance.

Walking fields and taking notes will help farmers determine an action plan for next year. What we’re seeing now in the fields can have an impact on what we see in the future.

Phytophthora root and stem rot is a significant disease affecting soybeans across Latham Country. It can kill and damage seedlings and plants from planting almost through harvest. This disease especially favors saturated conditions early in the growing season.

You’re most likely to find Phytophthora in the following places:

• Low, wet spots in a field
• Fields with high clay content
• Fields that have been in no-till for a few years
• Weedy areas that may be the result of stand reduction earlier in the season

Begin scouting as early as emergence where soils are saturated by heavy rains following planting. Where gaps in the row appear, carefully dig down to the seed zone. Infected seeds may rot before germination. Others may germinate but fail to make it to the surface.

In other instances, soybean plants may emerge from the soil and then die. These dying or dead plants often show a “pinching” of the stem just at or slightly below the soil line. This symptom is commonly referred to as damping-off.

If damping-off is a problem in the spring, watch for Phytophthora infection following rainy periods later in the season. The stem rot phase is easily recognizable by the presence of a distinct chocolate-brown lesion moving up the stem from the soil line. Initially, the upper stem of the plant may remain green. The plant will eventually wilt, turn yellow, and then die with leaves remaining attached.

The root rot phase of Phytophthora is not as readily recognized as the stem rot phase. Infected plants can be stunted and less vigorous, although this is hard to spot unless the infected plants are near a healthy comparison. A close inspection of the root system will reveal a significant reduction in the number of secondary roots and fine root hairs that help the plant take up moisture and nutrients. Plants with the root rot phase may mature a week or two earlier than healthy plants in the field.

Management

Many soybean varieties have resistance genes. The most common group of genes are known as Rps genes (“Resistant to Phytophthora sojae”). Varieties with “stacked” genes can show significantly higher resistance to Phytophthora. Specific information on PRR genes for each of Latham® soybean varieties is included in our 2023 Seed Guide.

Using Latham’s SoyShield® and SoyShield Plus seed treatments is a proven, effective way to protect against early-season diseases like Phytophthora. Using our seed treatment gives you the confidence and flexibility for a strong start to the growing season.

*Sources:

• Phytophthora Root & Stem Rot – Soybean Disease – Soybean Research & Information Network – SRIN (soybeanresearchinfo.com)
• Phytophthora root and stem rot on soybean | UMN Extension

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