With the burgeoning market for CBD, it is no wonder hemp cultivation has taken off in many US states. But successfully growing this crop means finding the right conditions, as some growers in Arizona are discovering the hard way.
Last summer, about 85 percent of drip-irrigated industrial hemp plants in Yuma and Graham counties experienced symptoms of crown and root rot, a serious disease that leads to leaf yellowing and browning, sudden wilting and plant death.
Agronomists at the University of Arizona identified the fungus-like pathogen behind these hemp crop losses as Pythium aphanidermatum, also known as water mold.
Pythium species prefer damp environments and infect a range of agricultural crops, including beets, carrots, peppers, corn, and wheat. They can affect hemp at any stage of growth.
Pythium crown and root rot is seen when hemp is grown in hot climates and in heavy soils with poor drainage, using plastic mulch and excessive irrigation.
The authors say this fungal disease may limit industrial hemp production in hot and dry environments where farmers rely on excessive irrigation, plastic mulch and soils with poor drainage, conditions prevalent on Arizona farms.
Infection can be minimized by ensuring crops are grown on soils with good drainage, regulating irrigation to prevent water saturation and removing mulch to reduce soil moisture. No fungicides have been registered for the management of Pythium species in hemp.
In 2019, farmers experienced off-the-charts crop losses after hemp crops exceeded 0.3% THC levels, which state authorities attributed to the hot climate. Hemp acreage fell from 5,430 acres in 2019 to 1,130 acres in 2020.