Soil-borne diseases are plant diseases caused by pathogenic organisms that inhabit the soil and attack the roots and lower stems of plants. These pathogens can be fungal, bacterial, viral, or nematodes. Soil-borne diseases are very common and can severely impact crop yields. However, there are several effective methods to prevent, control and treat soil-borne diseases.
Common Soil-Borne Diseases
Some of the most common and problematic soil-borne diseases include:
Fungal Diseases
- Damping-off – Caused by fungi like Pythium, Phytophthora, Rhizoctonia. It causes seedling death before or after emergence from soil.
- Fusarium wilt – Caused by Fusarium fungi and leads to wilting and death of older plants.
- Verticillium wilt – Caused by Verticillium fungi. Causes discoloration and wilting.
- Root rot – Caused by fungi like Phytophthora, Pythium and Rhizoctonia. Roots rot and turn brown or black.
- Clubroot – Caused by Plasmodiophora brassicae. Causes root swelling and growth stunting.
Bacterial Diseases
- Bacterial wilt – Caused by Ralstonia solanacearum. Vascular tissues get clogged leading to wilt.
- Crown gall – Caused by Agrobacterium tumefaciens. Leads to tumour-like growths on roots and crowns.
Viral Diseases
- Tobacco mosaic virus – Mottling, discoloration and stunting of leaves and shoots.
- Tomato spotted wilt virus – Bronzing and spots on leaves, rings on fruits.
Nematode Diseases
- Root knot nematodes – Caused by Meloidogyne spp. Leads to galls and swelling on roots.
- Cyst nematodes – Caused by Heterodera and Globodera spp. Cysts develop on roots damaging plants.
- Lesion nematodes – Caused by Pratylenchus spp. Migrate through root tissue causing cell death.
Preventing Soil-Borne Diseases
An effective soil-borne disease control strategy focuses heavily on prevention. Some key preventive measures include:
Crop Rotation
Rotating between crops from different families prevents the buildup of pathogens specific to one crop in the soil. For example, rotate between lettuce (Asteraceae) and beans (Fabaceae).
Resistant Varieties
Choose disease-resistant cultivars which are bred to have genetic resistance against certain pathogens.
Sanitation
Disinfect gardening tools, pots and trays to prevent spreading pathogens between plants.
Soil Solarization
Heating moist soil under plastic sheets kills pathogens, nematodes and weeds in top layers.
Raised Beds
Growing crops in raised beds improves drainage and reduces surface contact between plants and pathogen inoculum.
Irrigation Management
Avoid over-watering and improve drainage to minimize conducive conditions for disease development.
Weed Control
Weeds can harbor pathogens. Remove weeds promptly and avoid spreading during cultivation.
Soil Amendments
Adding compost and organic material promotes microbial activity in soil that helps suppress pathogens.
Treating Soil-Borne Diseases
If preventive measures fail and plants become infected, here are some effective treatment options:
Fungicides
Apply targeted fungicides like metalaxyl, mefenoxam or phosphites to control Oomycete fungi like Pythium and Phytophthora. Avoid excessive use.
Bactericides
Copper-based bactericides like copper hydroxide can treat bacterial diseases like bacterial wilt. Avoid phytotoxicity from over-application.
Solarization
Solarizing infected soil again by covering with plastic sheets for 4-6 weeks helps reduce inoculum.
Heat Treatment
Heating infested soil to 140°F for 30 minutes using steam or infra-red treatments kills pathogens.
Biofungicides
Apply fungal antagonists like Trichoderma and bacterial antagonists like Bacillus subtilis to biologically control soil pathogens.
Organic Amendments
Amending soil with compost, manures, green manures or chitin can promote beneficial microbes and reduce pathogens.
Crop Rotation
Rotating to a non-host crop for 2-3 years allows pathogen populations to decline before replanting.
Flooding
Temporarily flooding fields 2-4 weeks before planting can reduce pathogen populations.
Resistant Varieties
Switch to resistant varieties to limit disease impacts.
Roguing
Promptly remove and destroy severely infected plants to limit pathogen spread.
Key Measures for Specific Diseases
Damping-off
- Use sterile soilless media for seedlings
- Apply fungicide drenches like mefenoxam
- Lower seeding density
- Ensure warm temperatures (65-85°F) for germination
Fusarium Wilt
- Grow resistant tomato cultivars
- Solarize soil before planting
- Rotate out of solanaceous crops for 3+ years
Verticillium Wilt
- Rotate with non-hosts like grasses or cereals
- Apply biofungicides with Streptomyces
- Rogue early infections promptly
Root Rot
- Improve drainage and avoid over-watering
- Apply phosphonic acid fungicides
- Use raised beds for better soil aeration
Bacterial Wilt
- Rotate with cereal crops for 2-3 years
- Apply copper sprays before disease onset
- Rogue infected plants quickly
Root-Knot Nematodes
- Rotate with cereals like sorghum or marigolds
- Apply bio-nematicides with Paecilomyces lilacinus
- Use resistant tomato and pepper varieties
Conclusion
Soil-borne diseases can be very challenging to manage. An integrated approach using preventive, cultural, biological and chemical measures is key. Focus on improving soil health through additions of organic matter and beneficial microbes. Employ targeted treatments when infections occur, but avoid over-reliance on any single method. With vigilance and diverse tactics, soil-borne disease impacts can be minimized without resorting to detrimental practices. By implementing a sound rotation plan, nurturing the soil biome, choosing resistant varieties and applying treatments judiciously, gardens and farms can flourish even in the presence of stubborn soil pathogens.
FAQs about Soil-Borne Diseases
What are the most common soil-borne diseases?
Some of the most common and problematic soil-borne diseases are damping-off, Fusarium wilt, Verticillium wilt, root rot, clubroot, bacterial wilt, crown gall, root knot nematodes, cyst nematodes and lesion nematodes. They are caused by fungal, bacterial, viral and nematode pathogens.
How do soil-borne diseases affect plants?
Soil-borne pathogens infect plant roots and stem bases leading to poor growth, wilting, stunting, rotting of roots, galls or lesions on roots and blockage of water transport resulting in dieback of shoots. They severely reduce plant vigor and cause economic losses.
How do soil-borne pathogens spread?
Pathogens spread via soil water, infected soil amendments, contaminated equipment, infected transplants, run-off water and irrigation. Those producing survival structures like chlamydospores, sclerotia or cysts persist in soil for years. Nematodes actively migrate through soil.
How can soil-borne diseases be prevented?
Crop rotation, disease-resistant varieties, sanitation of tools, soil solarization, raised beds, improved drainage, weed control, adding organic amendments and biofungicides help prevent buildup of soil pathogens. Avoiding injuries to roots and stresses also lowers incidence.
What is the best way to control soil-borne diseases?
An integrated approach using preventive measures like crop rotation together with soil amendments to enhance microbial activity provides the most effective control. Targeted fungicide/bactericide drenches or biofungicides can be used to supplement when required.
How do you treat diseased plants and soil?
Infected plants can be treated with fungicidal drenches or sprays. Overhead watering should be avoided. Infested soil can be solarized, heated or amended with compost and antagonistic microbes to reduce pathogen load before replanting. Biofungicides as soil drenches at planting help protect new plants.
Should you replace soil infected with soil-borne diseases?
It is usually not necessary to replace all the soil, but removing severely infested parts can help. The main aim should be to enhance microbial activity and beneficial organisms that suppress pathogens. Introducing amendments like aged compost or manure and practicing crop rotation is typically adequate over time.
Are soil-borne diseases more common in potting mix or in-ground?
Container plants are more prone to soil-borne pathogens due to confinement of the roots and more frequent irrigation resulting in overly moist media. However, in-ground plants can also be severely affected in cases of poor drainage or heavy pathogens loads. Maintaining optimal soil conditions is key in both situations.
How long do fungal pathogens survive in soil?
Survival periods vary widely based on the pathogen. Fusarium and Verticillium can persist for 10-15 years. Phytophthora and Pythium survive for 2-5 years as thick-walled spores. Rhizoctonia and nematodes may only survive for a few weeks or months. Rotating crops and improving soil health helps lower inoculum.
Conclusion
Vigilance and prompt action are vital in dealing with soil-borne pathogens. Focus on preventive measures first to avoid the need for treatment. When infections do occur, employ a combination of methods tailored to the specific pathogen. Improving overall soil health by enhancing microbial diversity, structure and organic matter content helps create conditions where crops can thrive despite the presence of endemic soil pathogens. An integrated disease management plan is essential for effective, sustainable control.
Soil-borne diseases can be very challenging to manage. An integrated approach using preventive, cultural, biological and chemical measures is key. Focus on improving soil health through additions of organic matter and beneficial microbes. Employ targeted treatments when infections occur, but avoid over-reliance on any single method. With vigilance and diverse tactics, soil-borne disease impacts can be minimized without resorting to detrimental practices. By implementing a sound rotation plan, nurturing the soil biome, choosing resistant varieties and applying treatments judiciously, gardens and farms can flourish even in the presence of stubborn soil pathogens.