Kentucky Industrial Hemp: Southern Blight – What You Need to Know

A fungal mat of mycelia (white fungal strands) with tan-colored sclerotia develop on infected hemp stems. (Photo: Clint Walker, grower, photo courtesy of Alan Windham, University of Tennessee)

In 2018, there were significant increases in confirmed cases of southern blight in hemp.  The fungal disease affects a wide range of plant species, as well as hemp. When stems and roots become infected, plants can wilt, decline, and/or die, resulting in yield loss.

The southern blight pathogen survives in upper soil layers for many years, increasing the risk for subsequent susceptible crops planted in the same area. No fungicides are labeled for hemp, so management relies on an intensive cultural program.

Southern Blight of Hemp Facts

  • The first observed symptoms often include wilting, dieback, and decline. With closer inspection, brown lesions on lower stems, crown rot, and/or root decay may be visible. Under conditions of warm temperatures and high humidity, white fungal mats (mycelia) and tiny round fungal structures called sclerotia (white when immature, and tan when mature) may be present (Figure 1).
  • This soil-borne pathogen survives as sclerotia in soil and as mycelia on plant residues. Sclerotia can persist for many years in upper layers of soil.
  • Conditions favoring disease development include high moisture in soil and pant canopies and relatively high temperatures (81° to 95°F). This summer was hot and wet across much of the Commonwealth, and disease increased as a result.
  • Spread can occur by running water and movement of infested soil, plant debris, tools, equipment, and transplants.
  • Caused by the fungal organism Sclerotium rolfsii.

Management Options

  • Avoid planting hemp in areas with a history of southern blight.
  • Plant only healthy, disease-free transplants into field sites.
  • Rotate to a non-host plant, such as corn or small grains, for 3 to 4 years.
  • Manage weeds to reduce alternative hosts.
  • Remove and destroy infected plants. Remove soil surrounding infected plants, when possible.
  • Deep till affected sites to move sclerotia and infected plant debris deeper into the soil profile.
  • Increase plant spacing to improve air circulation.
  • When infection occurs in greenhouses or high tunnels, solarization can be used to reduce pathogen levels in ground beds.
  • No fungicide options are available for hemp growers at this time.

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