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Stem Canker

Overview

Stem Canker, caused by fungi in the Diaporthe and Phomopsis genera, is a significant disease affecting soybeans and other crops in the US and Canada. The disease manifests as dark, sunken lesions on the stems, often near the nodes, which can girdle the stem and disrupt nutrient and water transport. This leads to wilting, premature leaf drop, and plant death.

Stem Canker thrives in warm, wet conditions, particularly in fields with high humidity and poor air circulation. Yield losses can be substantial, ranging from 10% to 50%, depending on the severity of the infection and environmental conditions. Effective management includes crop rotation with non-host crops, planting resistant soybean varieties, and applying fungicides at critical growth stages.

Products like Priaxor® Xemium® brand fungicide and Headline® fungicide can help manage the disease. Early detection and integrated disease management strategies are crucial to mitigating the impact of Stem Canker on crop productivity.

How to Identify Stem Canker

Identifying Stem Canker involves observing specific symptoms on the plants. Here are detailed steps to identify Stem Canker:

1. Field Symptoms

  • Patchy Distribution: Similar to Brown Stem Rot, Stem Canker often appears in patches within a field rather than uniformly distributed.

2. Stem Symptoms

  • Cankers on Stems: The most characteristic symptom is the presence of cankers on the stems. These cankers are elongated, sunken, and dark brown to black in color.

  • Location of Cankers: Cankers typically develop at the nodes (where leaves attach to the stem) and can extend up and down the stem. In Northern Stem Canker, cankers are usually found on the lower part of the stem, while in Southern Stem Canker, they can be found higher up.

  • Girdling: As the cankers enlarge, they can girdle the stem, cutting off the flow of water and nutrients, which can lead to plant death.

3. Leaf Symptoms

  • Interveinal Chlorosis: Leaves may show interveinal chlorosis (yellowing between the veins) and necrosis (dead tissue), which can be mistaken for other diseases or nutrient deficiencies.

  • Wilting and Death: In severe cases, the entire plant may wilt and die, especially if the stem is girdled by the canker.

4. Root Symptoms

  • Healthy Roots: Unlike some other diseases, the roots of plants affected by Stem Canker often appear healthy, which can help differentiate it from root rot diseases.

5. Timing of Symptoms

  • Mid to Late Season: Symptoms typically appear from mid-season to late-season, often during the reproductive stages (R3 to R6).

6. Environmental Conditions

  • Warm, Wet Conditions: Stem Canker is more prevalent in warm, wet conditions, which favor the growth and spread of the fungus.

7. Laboratory Confirmation

  • Microscopic Examination: For definitive diagnosis, samples can be sent to a plant pathology lab where the fungus can be isolated and identified under a microscope.

Management Tips

  • Resistant Varieties: Planting resistant soybean varieties is the most effective way to manage Stem Canker.

  • Crop Rotation: Rotate soybeans with non-host crops like corn to reduce the pathogen load in the soil.

  • Field Sanitation: Remove and destroy infected plant debris to reduce the source of inoculum.

  • Fungicide Application: In some cases, fungicides may be applied as a preventive measure, especially in fields with a history of Stem Canker. Always follow label recommendations and consult with an agronomist for the best timing and product choice.

If you suspect Stem Canker in your field, it's crucial to take action promptly to manage the disease and prevent further spread.

Geographic Impact of Stem Canker

Stem Canker, caused by the fungus Diaporthe phaseolorum, has a significant geographic impact, particularly in soybean-growing regions. The disease is divided into two main types based on geographic distribution and climatic conditions: Northern Stem Canker and Southern Stem Canker.

Northern Stem Canker

  • Geographic Distribution: Primarily found in the northern soybean-growing regions of the United States, including states like Iowa, Illinois, Indiana, Minnesota, and Ohio.

  • Climatic Conditions: Prefers cooler, wetter climates. The disease is more prevalent in areas with moderate temperatures and high humidity during the growing season.

Southern Stem Canker

  • Geographic Distribution: Predominantly affects the southern soybean-growing regions of the United States, including states like Arkansas, Mississippi, Louisiana, Tennessee, and parts of Texas.

  • Climatic Conditions: Thrives in warmer, wetter climates. The disease is more common in areas with high temperatures and humidity, particularly during the growing season.

Global Impact

  • North America: Besides the United States, Stem Canker can also be found in soybean-growing regions of Canada, particularly in Ontario and Quebec.

  • South America: The disease is present in major soybean-producing countries like Brazil and Argentina, where it can cause significant yield losses.

  • Asia: Stem Canker has been reported in soybean fields in countries like China and India, where soybeans are a major crop.

  • Europe: While less common, the disease can also occur in European countries that grow soybeans, such as Italy and Ukraine.

Timing of Stem Canker Impact

Stem Canker in soybeans typically emerges and impacts fields at specific times during the growing season. The timing can vary slightly depending on the type of Stem Canker (Northern or Southern) and the geographic location. Here’s a detailed overview:

  1. Infection Period

    • Early to Mid-Growing Season: The initial infection usually occurs early in the growing season, often during the vegetative stages (V1 to V6). The fungus infects the plant through natural openings or wounds in the stem, such as those caused by cultivation or insect feeding.

  2. Symptom Development

    • Mid to Late Growing Season: Symptoms of Stem Canker typically become visible from mid-season to late-season, often during the reproductive stages (R1 to R6). This is when the cankers on the stems become noticeable, and leaf symptoms may appear.

How to Manage Stem Canker

To chemically treat stem canker, consider using the following products.

For Soybeans

  • Willowood Propicon 3.6EC: This fungicide contains Propiconazole and is effective against Stem Canker in soybeans. It can be applied as a preventive measure, especially in fields with a history of the disease. You can purchase it from FBN here.

For Other Crops

While Stem Canker primarily affects soybeans, similar fungal diseases can impact other crops. Here are some general recommendations for managing fungal diseases in other crops:

  • Corn: For fungal diseases in corn, products containing active ingredients like Azoxystrobin - such as GCS Azoxy 2SC - or Pyraclostrobin can be effective. These fungicides help manage a range of fungal pathogens.

  • Wheat: For wheat, fungicides containing Tebuconazole - such as Willowood Teb 3.6SC - or Propiconazole - such as Willowood Propicon 3.6EC - can be used to manage fungal diseases. These products help protect the crop during critical growth stages.

By combining these cultural practices with appropriate chemical treatments, farmers can effectively manage Stem Canker and other fungal diseases in their crops. Always follow label recommendations and consult with an agronomist for the best timing and product choice.

Willowood Propicon 3.6EC
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