I was recently visiting a greenhouse admiring the health of their begonia plants. The foliage looked healthy and robust. I was sure they would sell quickly at garden centers. Then, as I always do, I pulled a plant from cell pack and looked at the roots. My initial appraisal of the plants' health soon turned. The roots were darkly discolored, soft, and rotting (see image). Although the foliage did not show symptoms of root disease, the roots had all the classic symptoms of Pythium root rot. These plants were doomed.
by Jean Williams-Woodward
Current weather patterns where warmer spring weather is intermittently broken by frosts and excessive rainfall can contribute to scheduling delays and holding plants. During this period, plants may become more susceptible to root infections. There have been several e-GRO Alerts on root diseases and their management. The primary root pathogens affecting bedding plants are Pythium spp. and Berkeleyomyces basicola (formerly Thielaviopsis basicola). Don’t get my started on fungal name changes. I don’t like the new name either. Regardless of the new name, black root rot is very common right now on pansy, snapdragon, vinca, and petunia bedding plants.
See the e-GRO Alerts "Pythium in Propagation" (http://www.e-gro.org/pdf/2019_804.pdf) and "Pythium Problems" (http://www.e-gro.org/pdf/2017_608.pdf) for more information on Pythium disease development and management. Information on Berkeleyomyces (Thielaviopsis) can be found in the e-GRO Alert, “Black Root Rot on Pansy” (http://www.e-gro.org/pdf/2016_513.pdf). The best way to reduce root disease and pathogen introduction is to follow good sanitation practices. See the e-GRO Alert “Sanitation: Start clean, stay clean!” (http://www.e-gro.org/pdf/2018_731.pdf) for more information.
Source: eGRO Blog