Over the last month, dieback symptoms have been widely observed in hemp stands. These symptoms are characterized by wilting and necrosis of branch tips. These symptoms could be caused by several different diseases.
Currently, there are no effective chemical management strategies that are legal for use in industrial hemp at this time. Management for these diseases revolves around similar strategies. Reduce excess moisture in the field where possible. Destroy crop debris quickly at the end of the growing season to limit inoculum survival.
Planting consecutive seasons of industrial hemp favors disease, and crops should be rotated with non-host plants.
1. Tip Dieback (Lassidiplodia crassispora)
Dieback caused by fungi in the Botryosphaeriaceae can cause tip dieback. Infections begin in the stems, often following physical injury from insects or other mechanical injuries. Lesions caused by these pathogens often cause black vascular discoloration.
2. Rhizoctonia Web Blight (Rhizoctonia solani)
Blight caused by Rhizoctonia solani begins at the top of the plants. Leaves become necrotic and stay attached to the plant. Fungal webbing can be seen between leaves.
3. Fusarium Stem Canker (Fusarium graminearum)
Stem cankers caused by Fusarium spp. begin low on the stalk following periods of warm temperatures and high humidity or rainfall. Vascular tissue within affected stems show pink-brown discoloration. Tops of plants wilt and leaves brown. Plants may become girdled and lodge.
4. Hemp Canker (Sclerotinia sclerotiorum)
Hemp canker caused by Sclerotinia spp. cause lesions on lower stems. Plants wilt, and dieback. The vascular tissue becomes shredded and within the dead tissues, black, irregularly-shaped sclerotia may be found.
For diagnostic support, samples can be confirmed at the diagnostic clinic. Consult the clinic website for sample submission requirements.