See:
Hemp (Cannabis sativa) - Fusarium Wilt
Cause Two fungi, Verticillium dahliae and Verticillium albo-atrum, which can survive in diseased plants. Both of these fungi have a broad host range and can infect numerous other plant species. Verticillium dahliae can also survive in the soil as durable, long-lived structures known as microsclerotia which can persist for years. These fungi infect through plant roots. These fungi can be spread through soil movement on equipment, tools, and footwear as well as infested soil being windborne or waterborne. These pathogens can be introduced into a new region through the movement of infected transplants or the sowing of infected seed.
Symptoms Plants are susceptible at any stage. Early symptoms include yellowing of lower leaves, sometimes one-sided or V-shaped in appearance, and stunting of the plant. Leaves may die, and leaf yellowing as well as defoliation may progress up an affected cannabis plant. Wilting of plants is observed more commonly once flowering commences and yellowing spreads to younger leaves. Often the entire plant dies and remaining stems are silvery-tan in color. Dark-brown to blackish discoloration can found around vascular elements in roots and in stems. Vascular discoloration precedes wilting symptoms. A brown rot may develop on the tap root or the lower stem of affected plants. The root system may also be stunted with a brown rot of the lateral roots present.
Cultural control
- Avoid establishment of hemp fields in soils where hemp wilt occurred in the previous three years.
- Rotate to grasses and cereals for several years if wilt is caused by Verticillium.
- Avoid planting in heavy, poorly draining soils.
- Avoid excessive irrigation, especially during the spring, but also minimize moisture stress, particularly during flowering.
- Apply sufficient nitrogen for crop needs, but avoid excessive fertilization of this nutrient and use a nitrate form rather than ammonia.
- Clean tools and equipment between fields so that there are no remaining soil or plant residues that can lead to pathogen spread.
- Remove and destroy diseased plants while avoiding contact with healthy plants; this will decrease the build-up of durable fungal structures. Burn or deeply bury infected plants.
- Soil solarization can weaken and reduce soilborne populations of Verticillium. See http://westernipm.org/index.cfm/ipm-in-the-west/agriculture/soil-solariz... forhttps://aces.nmsu.edu/programs/sare/documents/2019_parke.pdf for more information on soil solarization in the Pacific Northwest. Soil solarization can also help with the management of other soilborne pathogens as well as weed seed banks in the soil.