Hemp Diseases in North Florida

by | Mar 19, 2021 | Disease, Field Crops, Hemp, Hemp, Horticulture, Pest Management

Fanny Iriarte, Josh Freeman, Rui Yan, and Matthews Paret, UF/IFAS North Flroida Research and Education Center

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The following are a collection of hemp diseases and the associated symptoms for diagnosis, as well as management tips to reduce yield loss or plant death.

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Bacterial Spot – Xanthomonas campestris pv. campestris

Hemp Bacterial Spot Symptoms

Management

  • In early stages of disease removing infected plant material in lower canopy may help reduce infections.
  • Avoid wounding
  • Avoid overhead irrigation
  • Increase plant spacing to improve air circulation.
  • Currently there’s no chemicals labeled for Industrial hemp.

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Bipolaris leaf spot – Bipolaris spp.

Bipolaris Leaf Spot Symptoms

Reported before in Kentucky and New York. Detected in Quincy, FL 6-03-20

Management

  • In early stages of disease development, remove infected plant material from field as soon as detected to reduce the amount of fungal inoculum in the field.
  • Control weeds, as they can serve as secondary hosts for pathogens and virus insect vectors.
  • Remove and/or destroy crop debris at the end of the growing season. This will help get rid or overwintering fungal inoculum.
  • Avoid or reduce overhead irrigation and improve aeration.

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Damping off – Rhizoctonia solani

Hemp Damping Off

Observed on greenhouse grown hemp seedlings. Damping off fungi invade stems of seedlings at the soil line shortly after they emerge.

Management

  • In greenhouse, growing medium should be sterilized and all containers disinfested before reuse.
  • Avoid over-watering and improve drainage.

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Fusarium flower blight – Fusarium spp. 

Fusarium Flower Blight

Fusarium graminearum and F. equiseti have been isolated from Hemp flowers (Thiessen L. 2020).

Important note

  • Infection of female flowers buds and grain may result in contamination by Fusarium mycotoxin.
  • Cornell Hemp group have found contamination of hemp grain in excess of 7 ppm of deoxynivalenol (vomitoxin) during a survey in 2019 (Bergstrom et.al. 2019).

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Fusarium Wilt – Fusarium oxysporum f. sp. vasinfectum* 

Hemp Fusarium Wilt symptoms

Management

  • In greenhouse, growing medium should be sterilized and all containers disinfested before reuse.
  • Avoid over-watering and improve drainage.

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Fusarium crown/root rot – Fusarium solani*

Hemp Fusarium Crown or Root RotManagement

  • Avoid low areas and improve drainage.

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Pythium lower stem, crown and root rot – Pythium myriotylum*

Hemp Pythium stem crown & root rot

Hemp Pythium stem & crown rotHemp Pythium stem & crown rot

Management

  • In greenhouse, growing medium should be sterilized and all containers disinfested before reuse.
  • Avoid low and poorly drained areas.
  • Remove and discard infected plant material away from the site to avoid spread of the pathogen in the field.
  • Fungicide treatment studies are under way.

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Southern blight – Athelia rolfsii (Sclerotium rolfsii)


Hemp Southern Blight

Management

  • Avoid planting hemp in areas with history of Southern Blight.
  • Plant healthy transplants.
  • Remove and discard (away from the field) infected plant material as well as soil around it to avoid spread of the pathogen.
  • Increase plant spacing to improve air circulation.
  • After harvesting, deep plowing to bury pathogen sclerotia is recommended to reduce fungal inoculum in the soil profile.
  • Currently there are no chemicals labeled for Industrial hemp.

For more information see:  Southern Blight of Industrial Hemp (lsuagcenter.com)

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INDUSTRIAL HEMP DISEASE TESTING

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References and Other Resources

FLORIDA

OTHER STATES

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