P-058 - Interdisciplinary Evaluation of Organic Fungicides and Biostimulants for Managing Lettuce Fusarium Wilt in California

Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. lactucae, is a devastating soil-borne disease impacting lettuce production worldwide. As a vascular pathogen, it restricts water and nutrient uptake causing profound physiological stress that limits growth and yield, particularly under high temperatures. Certain microbes such as Bacillus, Pseudomonas, and Trichoderma have been known to benefit host plants by reducing abiotic stress and outcompeting pathogens. With their increasing availability as commercial formulations, growers face uncertainty in selecting and utilizing effective products for improved plant health in lettuce production systems. To address this, multiple greenhouse studies were conducted on iceberg lettuce using varied inoculation methods and a diverse set of commercial treatments to assess both disease suppression and biostimulant effects. Disease severity ratings and physiological assessments with a porometer/fluorometer were taken weekly. In highly disease-conducive conditions, most products failed to suppress disease after two applications and showed minimal detectable physiological improvements compared to untreated controls; however, a biostimulant containing Paenibacillus chitinoliticus, B. subtilis, B. pumilus, and B. amyloliquefaciens has demonstrated improved stomatal conductance of up to 69% compared to the inoculated UTC. This interdisciplinary approach can help both manufacturers and growers to identify effective products and optimize treatment application rates and timings for sustainably managing Fusarium wilt.