Pythium: Hemp Disease to Look Out For
Several species of Pythium from both greenhouse and field production of hemp have been identified in Utah. To date we have found three species – Pythium ultimum, P. dissotocum and P. myriotylum. P. ultimum has a wide host range including vegetables and field crops. P. dissotocum is found on lettuce, and P. myriotylum is found on vegetables but usually in warmer climates. So far, P. myriotylum was only found in greenhouses.
The symptoms consist of root rot and stunted plants (Fig. 1) for P. ultimum and P. myriotylum. The outer layer of the roots comes off easily leaving only the core layer. In the case of crown rot, the pathogen entered the crown right at the soil line and subsequently colonized and rotted the crown area. P. dissotocum did not cause a root but rather a crown rot on older plants. The tissue of the stem is discolored, which can be seen in Fig 2 and 3.
Method of infection
Pythium is a soilborne pathogen that likes wet conditions. It produces spores that can swim in a film of water using flagella (hairlike appendages) to move themselves forward. Management of Pythium on hemp is difficult and there is currently very little information. Based on Pythium diseases in other crops the following recommendations are made.
Recommendations so far
In the field, the best option is using drip irrigation and avoiding stem wetting. In a greenhouse setting it is important to keep benches, pots and tools clean and sterilized using a 10-15% bleach solution or other disinfectant. Pythium can be in residual potting mix in pots from the previous crop. When mixing potting soil, using a tarp to avoid the potting mix coming into contact with the bare ground can minimize contamination.
Which Diseases to Watch for in Hemp