CALIFORNIA
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Tomato variety key to controlling fusarium stem rot By Vicky Boyd Fusarium stem rot and decline, commonly known as FRD, affects the water- and nutrient-carrying vascular portions of processing tomato plant stems and canopies. Eventually, vines begin to decline, collapsing and exposing the fruit to the sun, leading to potential sunburn.
Ag Seeds Unlimited joined the collaborative effort in 2021, and Lazicki started in 2023 when she was hired by UCCE. The California Tomato Research Institute is supporting their work. Each year, Ag Seeds grows the transplants, and plants replicated trials in farmers’ com- mercial fields infested with soil-borne pathogens, said Ross Lopez, an Ag Seeds salesper- son also involved with product development. Rarely does a field have a single pathogen, so he said the company typically screens for multiple diseases. This year, Ag Seeds planted 11 trials, each featuring the same 29 popular varieties. During the season, the seed dealer and UC rate them for disease symptoms and vine decline. If the cause is questionable, they may pull samples to send to Cassandra Swett’s pathogen diagnostic laboratory at UC Davis. A commercial processing tomato harvester picks the plots, transferring the fruit to a modified gondola cart with a weight cell to measure yields before conveying them to commercial trailers. Through the years, the trials have evolved. “They used to be just strip trials of varieties side by side, with no yield information. It was just visual ratings,” Lopez said. They’ve found that no variety has true FRD resistance, although some varieties ap- pear more tolerant, Aegerter said. Even then, some varieties may not yield well under
As experts learn more about a relatively new fungal disease of processing tomatoes, they say variety selection is key to reducing potential yield losses. Crop rotation and equipment sanitation also are important in managing fusarium stem rot and decline, though to lesser extents. “I think the variety and sanitation would be my top priorities,” said Brenna Aegerter, University of California Cooperative Extension vegetable crops farm adviser who serves San Joaquin County. Rotating to a nonhost crop can help reduce the pathogen in the soil, but she said it’s not too popular because many of the alternatives are unprofitable. Fusarium stem rot and decline, often referred to as FRD, is found in scattered fields from Kern County to the northern Sacramento Valley. But the bulk of the infections are centered in the northern San Joaquin and southern Sacramento Valley processing toma- to-production areas. Patricia Lazicki, UC vegetable crops farm adviser for the southern Sacramento Valley, said FRD is the issue that generates the most calls from growers. In 2025, it comprised about 30% of her diagnoses. In the northern San Joaquin Valley, the disease is scattered but still common, Aegerter said. For the past seven years, Aegerter has been part of a UC team researching FRD. From the beginning, she conducted trials to screen for varietal disease resistance. Woodland-based
See FUSARIUM, Page 11
10 Ag Alert August 5, 2026
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