Soil Fungus

Asked June 5, 2020, 2:38 PM EDT

Hello, I have soil fungus in one of my garden beds. I would like to test the soil to see exactly what type it is. I can see that there is wilt fungus for one because of the tomato plants looks wilted. I understand I will have to dig up the plants in this bed and throw them in trash as well as cover the soil with plastic for the moment. I do need to treat it, but am unsure how to go about it.

Clackamas County Oregon

3 Responses

Many common fungal or viral diseases can lay dormant in the soil for years until environmental conditions become just right for their growth or specific host plants are introduced. For example, the pathogen Alternaria solani, which causes early blight can lie dormant in the soil for several years even if no tomato plants are present, but once planted, the disease will begin to spread.

Soil testing for garden problems before planting the garden can help prevent disease outbreaks by giving gardeners a chance to amend and treat the soil or select a new site. Just as soil tests are available to determine nutrient values or deficiencies in the soil; soil can also be tested for disease pathogens. For a fee soil samples can be sent to laboratories; you can purchase test kits online, or at a local garden center.

These tests check garden soil for disease pathogens using a scientific system known as the ELISA (enzyme-linked immunosorbent assay) test and usually require you to mix soil samples or mashed plant matter with different chemicals that react to specific pathogens. Unfortunately, these tests are very specific for certain pathogens but not all. Several tests or test kits may be required to diagnose a plant disease. Viral diseases require different tests than fungal diseases. For more information about these tests refer to this publication from the University of California.

Fusarium wilt is a fungus that can survive for years in the soil and is spread by water, insects, garden equipment (including gloves), hands, and footwear. The fungal disease develops during hot -weather and thrives best when soil temperatures are between 75-80˚F. Dry weather and low soil moisture encourage this plant disease. Also, raising the pH level of your soil to 6.5 to 7.0 creates a fungus-resistant environment.


  1. Plant resistant varieties when available.
  2. Remove stricken growth from the garden and sterilize clippers (1-part bleach to 4 parts water) between cuts. For routine disinfecting of equipment use 1:9 bleach to water ratio.
  3. Control garden insects some of which are known to spread the disease; encourage beneficial insects.
  4. High nitrogen fertilizers may increase susceptibility to the disease. Test your soil regularly and use a slow-release, organic fertilizer in your vegetable garden.
  5. Hand pull or spot treat weeds using a natural herbicide; many weed species host the disease pathogen.
  6. Use a biological fungicide that will safely protect crops against wilt caused by Fusarium.
  7. If the disease persists, it is best to remove the entire plant and solarize the soil before planting again.

To solarize the soil, you must leave a clear plastic tarp on the soil surface for 4-6 weeks during the hottest part of the year. For step-by-step instructions on solarization and its benefits please refer to this UC IPM publication. Best of luck and happy gardening.

How on earth was this helpful? This is nothing different than I can research online. What I need is to test the soil. Do you not provide testing services any longer?

OSU Extension Service generally offers pH testing, but a fungus test is not a service we provide. Currently, OSU has mandated no in-person contact until further notice. SO to answer your last reply, "No, currently we are not providing any soil testing."

In my previous response, I did offer other viable options to get your soil tested for fungus pathogens.

Your inquiry, " well as cover the soil with plastic for the moment. I do need to treat it, but am unsure how to go about it." I provided a link for Step-by-Step instructions on how to go about it; covering your soil with plastic for solarization.

If, I have not covered your questions, respond back to this reply and I will do my best to do so. Good luck to you on the eradication of this most persistent pathogen.