Aerated steam eradicates powdery mildew from strawberry transplants

Authors: STENSVAND, ARNE - Norwegian Institute Of Bioeconomy Research(NIBIO); WANG, NAN-YI - University Of Florida; LE, VINH HONG - Norwegian Institute Of Bioeconomy Research(NIBIO); DA SILVA, CLAUDIO - Kansas State University; ASALF, BELACHEW - Norwegian Institute Of Bioeconomy Research(NIBIO); GRIEU, CHLOE - Norwegian Institute Of Bioeconomy Research(NIBIO); Turechek, William; PERES, NATALIA - University Of Florida

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2023
Publication Date: 8/12/2023
Citation: Stensvand, A., Wang, N., Le, V., Da Silva, C.D., Asalf, B., Grieu, C., Turechek, W., Peres, N.A. Aerated steam eradicates powdery mildew from strawberry transplants. European Journal of Plant Pathology. 168:199-205. 2023. https://doi.org/10.1007/s10658-023-02744-6.
DOI: https://doi.org/10.1007/s10658-023-02744-6

Interpretive Summary: Powdery mildew is an important disease in greenhouse production of strawberry. A modified steam thermotherapy protocol was evaluated as a means to eliminate powdery mildew from infected transplants in experiments conducted in Norway and Florida. Results showed that steam treatment could nearly eradicate (99%) powdery mildew with as little as two hours of exposure at 40 C following a preheat treatment of 37 C for one hour accompanied by a one-hour cooling period. This particular treatment is four degrees cooler and two hours shorter than a currently recommended steam treatment protocol used against other pathogens. These results showed that steam thermotherapy can eradicate powdery mildew from strawberry transplants at lower temperatures and exposure times than previously reported for other pathogens, which is cost effective for the producer, if powdery mildew is the target pathogen.

Technical Abstract: Powdery mildew, caused by Podosphaera aphanis, is an important disease of strawberry. A slightly modified version of a method using steam thermotherapy to rid diseases and pests from strawberry transplants was tested against strawberry powdery mildew. Experiments took place in Norway and Florida, with potted strawberry plants heavily infected with the fungus. Aerated steam treatments of the plants were carried out as follows: a pre-treatment with steaming at 37°C for 1 h was followed by 1 h at ambient temperature before plants were exposed to steaming at 40, 42, or 44°C for 2 or 4 h in Norway and 44°C for 4 h in Florida. Following steaming, plants from the different treatments and the untreated control were kept apart and protected from outside contamination of powdery mildew by growing them in closed containers with over-pressure. On steamed plants, hyphae of P. aphanis were dead and without any new spore formation after treatments, independent of temperature or exposure time; however, up to 99% of the area infected with powdery mildew prior to treatments contained actively sporulating lesions on non-steamed plants. None of the new leaves formed after steaming had powdery mildew, whereas more than half of the new leaves on non-treated plants were infected by P. aphanis. This investigation clearly indicates that steam thermotherapy can eradicate powdery mildew from strawberry transplants, and this can be achieved at lower temperatures and exposure times than previously reported for other pathogens.