Managing Soil-Borne Fungal Pathogens

October 8, 2025

Soil-borne fungal pathogens are one of the most persistent challenges farmers face. Diseases such as Phytophthora, Rhizoctonia, damping-off, Pythium, Verticillium, Fusarium, timber rot, and white mold can all cause significant yield loss and reduced crop quality. Once established, these pathogens can linger in the soil for years, making proactive soil management essential for long-term success.

To effectively manage soil-borne diseases, it’s important to understand that soil health, nutrition, and biology all work together. When the biological balance is restored and mineral nutrition is optimized, plants can resist or outgrow many of these fungal pressures naturally.

Understanding Soil-Borne Pathogens

Soil-borne pathogens are disease-causing organisms that live in the soil and infect plants through their roots. They often thrive in poorly drained, compacted, or biologically inactive soils. These pathogens can attack seeds, seedlings, or mature plants, causing root rots, wilting, and stunted growth.

Common soil-borne diseases include:

• Phytophthora root rot – thrives in wet conditions and affects a wide range of crops.

• Rhizoctonia root rot and damping-off – often strike seedlings soon after emergence.

• Pythium – causes seedling rot, particularly in cool, saturated soils.

• Verticillium and Fusarium wilts – long-lived fungi that block water flow in the plant.

• White mold and timber rot – common in vine crops and high-humidity environments.

Managing these diseases requires more than fungicides; it requires rebuilding the soil’s biological system so that beneficial organisms outcompete the pathogens.

Step One: Start with Biological Soil Preparation

Healthy soil biology is the first defense against soil-borne pathogens. Biological management focuses on creating an environment where beneficial microbes dominate the soil ecosystem, suppressing disease naturally.

An effective way to rebuild soil biology before planting is by applying microbial stimulants and carbon sources such as BioQuest Foundation. These products help restore microbial diversity, improve organic matter decomposition, and enhance disease suppression.

Another practical approach is to drip-irrigate 4 quarts of Rejuvenate and 4 quarts of SeaShield per acre about one to two weeks before planting. This timing gives beneficial organisms a head start, allowing them to occupy root zones before pathogens can take hold. Even when applied at planting, growers have reported strong results in reducing early disease pressure and improving root vigor.

Step Two: Use Cover Crops to Reduce Pathogen Pressure

Cover crops are one of the most powerful tools for improving soil structure and reducing disease pressure naturally. Among these, mustard cover crops stand out for their ability to suppress fungal pathogens and root rot nematodes.

When mustard plants reach full bloom, they release biofumigant compounds known as glucosinolates, which have a natural suppressive effect on soil-borne diseases. For best results:

1. Allow the mustard to bloom for 5–7 days.

2. Terminate and incorporate the biomass into the soil about two weeks before planting the next crop.

This approach has been especially successful in vine crops like watermelon, cantaloupe, zucchini, squash, cucumber, and pumpkin. It’s a sustainable way to break disease cycles while improving soil tilth and organic matter content.

Important Note for Cole Crops

Avoid planting mustard before growing cole crops such as broccoli, cauliflower, cabbage, kale, and brussels sprouts. Because they belong to the same plant family, they share similar diseases and pests. Instead, consider non-brassical cover crops like oats, rye, or clover before planting these vegetables.

Step Three: Introduce Biological Fungicides

Another valuable tool in integrated disease management is Serenade® ASO, an OMRI-listed biological fungicide containing a strain of Bacillus subtilis. This beneficial bacterium colonizes plant roots and creates an environment that discourages pathogens from thriving.

Unlike many traditional fungicides, Serenade ASO enhances the soil ecosystem instead of disrupting it. Research from Rutgers University by Dr. James White has shown that Bacillus subtilis can improve the rhizophagy cycle which is a natural process where plants feed on microbes to obtain essential nutrients.

Using Serenade ASO not only suppresses soil-borne pathogens like Rhizoctonia, Pythium, and Fusarium, but also improves root health and nutrient uptake. It can be used in transplant solutions, drip irrigation systems, or as a foliar spray, making it a flexible option for many cropping systems.

Contact our team for more information on Serenade ASO. 

Step Four: Strengthen Plant Immunity Through Nutrition

Even with excellent biological management, plant nutrition plays a vital role in disease resistance. Balanced mineral nutrition helps plants build stronger cell walls, produce defense compounds, and recover faster from stress.

Trace minerals are especially important in disease suppression:

• Manganese (Mn): Activates enzymes involved in plant defense and lignin formation.

• Copper (Cu): Strengthens cell walls and has direct antifungal properties.

• Zinc (Zn): Regulates hormone balance and enzyme systems critical for growth and recovery.

• Boron (B): Aids in cell wall development and sugar transport.

• Molybdenum (Mo): Supports nitrogen metabolism and overall plant vigor.
  

Regular sap testing during the growing season allows farmers to monitor nutrient levels in real time and adjust applications as needed. This proactive approach prevents deficiencies before they contribute to disease outbreaks.

Together, the above strategies strengthen the soil ecosystem, reduce pathogen pressure, and improve plant resilience to ultimately fend off unwanted diseases. 

Partner with a Regenerative Agriculture Consultant 

At Keystone Bio-Ag, we specialize in helping growers transition from reactive disease control to proactive soil health management. Our team offers expert consultation, sap testing support, and access to all-natural soil and crop enhancement products that build fertility while reducing dependency on synthetic chemicals.

If you’re facing challenges with soil-borne pathogens like Rhizoctonia, Fusarium, or Phytophthora, our agronomy specialists can help you develop a biological and nutritional plan tailored to your operation.

Contact Keystone Bio-Ag today to get started growing healthier, disease-free crops.