A Scientific Look at Diseases of Kentucky Hemp

 

Hemp Field Sanitation for Small-Scale Plantings

 IMPORTANCE OF SANITATION

Although hemp is considered a disease-free plant, it is unknown whether levels of certain pathogens can build up to problematic levels.  If diseases become a significant problem in field-planted hemp, results can include premature leaf drop, bud decay, dieback, decline, and even plant death.  When diseases do occur, it is often presumed that fungicides are the most important and effective disease management tools available.  However, there are limited fungicides available for use in hemp.  Thus, a good sanitation program can help reduce the need for chemical controls and can improve the effectiveness of other practices for managing disease.  This often-overlooked disease management tool reduces pathogen numbers and eliminates infective propagules (inoculum such as fungal spores and survival structures) that cause disease.  

 For example, certain fungal and water molds can become prevalent during rainy or humid growing seasons.  When disease management is neglected, pathogen populations build-up and continue to increase as long as there is susceptible plant tissue available for infection and disease development.  Infected plant tissue, infested soil, and pathogen propagules all serve as sources of pathogens that can later infect healthy plants. 

Reduction of pathogens by various sanitation practices can reduce both active and dormant pathogens.  While actively growing plants can provide host tissue for pathogen multiplication, dead plant material (diseased foliage, stems, and/or roots) can harbor overwintering propagules for months or years.  These propagules can travel via air/wind currents, stick to shoes or tools, or move with contaminated soil or water droplets.  Thus, prevention of spread of pathogens to healthy plants and the elimination of any disease-causing organisms from one season to another are the foundations for a disease management program using sanitation practices.


















 SANITATION PRACTICES

Elimination and/or reduction of pathogens from the plantings results in fewer pathogen propagules.  The following sanitary practices can reduce amounts of infectious pathogens:

  • Remove diseased plant tissues from infected plants.  Prune affected branches several inches below the point of infection.  Cuts should be made at an intersecting branch, if possible. 
  • Disinfest tools used to prune bacterial or viral diseases.  Cutting blades should be dipped into a commercial sanitizer, 10% Lysol disinfectant, 10% bleach, or rubbing alcohol between each cut.  If using bleach, rinse and oil tools after completing work, to prevent corrosion. 
  • Discard plants that are heavily infected and those with untreatable diseases (e.g. root rots and vascular wilts).  When practical, dig infected plants to include as much of the root system as possible.   
  • Plants infected with systemic diseases (e.g.Fusarium wilt) should be removed completely (upper plant parts as well as roots). 
  • Fungicides are more effective when pathogen levels are lower and diseased tissue is minimal.  Prune or remove infected tissue (flower buds, stems, leaves) and debris before fungicide applications. 
  • Discard fallen leaves, prunings, and culled plants.  Never leave diseased plant material in the field, as pathogens may continue to multiply by producing spores or other propagules.  Infected plant material should be buried, burned, or removed from the area altogether. 
  • Debris is a major source of infective propagules, including overwintering pathogens.  To the extent possible, rake and remove fallen leaves.  Always dispose of rotting or diseased plant tissue as soon as symptoms develop. 
  • Growers may plow under fallen leaves to promote the breakdown of leaf tissues.  This technique is only effective for tissues that decompose easily.  Woody stem  tissue does not respond to this treatment.
  • Do not compost diseased plant material or infested soil because incomplete composting (temperatures below 160˚ F) may result in survival of propagules.
  • Remove weeds and volunteer plants to prevent establishment of a “green bridge” between plants.  A green bridge allows some pathogens to infect alternate hosts until a more suitable one becomes available.  Remove aboveground parts AND roots. 


















 ADDITIONAL RESOURCES

Extension Plant Pathology Publications      http://www2.ca.uky.edu/agcollege/plantpathology/extension/pubs.html

 
Adapted from PPFS-GEN-05 Fruit, Orchard, and Vineyard Sanitation by Dr. Nicole Ward Gauthier, David Koester, and Faye Tewksbury.

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