The previous post described the importance of inspecting incoming plants and keeping a clean nursery to avoid pest introductions. Many important root pathogens and other pathogens, weeds, and insects can be introduced in contaminated soil and growing media, and so the focus of this post will be on ways to prevent introductions from these potential sources. 

Soil- inhabiting plant pathogens can be found in growing media and associated root and crop debris. Anything that has contacted the ground, such as equipment, tools, irrigation hoses, and workers' hands and shoes could be contaminated. Pots should not sit directly on the ground. Phytophthora  infecting  the roots of just one potted plant can produce thousands of propagules that can move in water draining from the pot and infect roots of  nearby plants.

Likewise, during a vigorous rain storm, these propagules can be splashed from the contaminated pot or ground onto nearby plants. Benches or similar structures that support plants above the ground can eliminate or minimize this.   In greenhouse structures, concrete floors or other impervious surfaces are ideal for walkways between benches. Floor surfaces should be kept clean of plant debris, soil, or growing media. After a crop cycle, benches should be cleaned of plant debris, washed and dried. Drying can kill sensitive plant pathogens.

 

Benches can be sprayed with diluted chlorine bleach (0.5 % sodium hypochlorite solution) or other suitable disinfectant. Potting media and plant debris will inhibit the activity of most disinfectants.

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are many clever ways to raise pots and containers off the ground.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Where benches or other support are not feasible for cost or other reasons, the soil should be covered with gravel and weed cloth. Gravel supports containers above the drainage water; the weed cloth (which also reduces weed germination) helps reduce splash and can be cleaned of soil and plant debris between crops .  

 

 

 

 

 

 

 

 

 

Pots, flats, tools, and irrigation equipment, such as piping or emitters, can have clinging contaminated soil and plant debris and should never be reused without thoroughly washing them to remove all clinging particles. They can then be treated with a disinfectant such as diluted chlorine bleach.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The bottom of clean shoes can be sanitized with disinfectants such as quaternary ammonium compounds . 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Growing media should not be reused, as the risk of pathogen carryover is too great and not worth the savings in most cases. Even some newly formulated media may benefit from steam treatment if the components of the media are unknown or unreliable.  Contact the potting media supplier to insure the media components are free of pathogens.  Aerated steam is the most efficient way of sanitizing potting media.

Portable steam generator for field or large area use.

Portable steam generators are available for sale or rent for small batches and commercial greenhouses may use the steam from boilers used for heating greenhouses. For most situations, aerated steam treatment of 140° to 160°F for 30 minutes will kill the most problematic pathogens while preserving the beneficial microflora of the growing medium.  

 

 

 

Store and handle growing media so it does not come in contact with the ground or water runoff.   Cover the media when not in use.