Fusarium Continued from Page 10
variety,” she said. Retired UCCE farm adviser Gene Miyao collected the first plants with suspected FRD in 2017. But it took Swett, an associate UCCE specialist in plant pathology, sever- al years to determine that a pair of related fusarium fungi was causing the issue. Al- though the two belong to the same large genus as the fusarium wilt causal organ- ism, they aren’t closely related, so varieties with fusarium wilt race 3 resistance are still susceptible to FRD. Initially, FRD-infected plants take on a yellowish or chlorotic cast, while leaves may be small and possibly curled, Aegert- er said. Lazicki said she frequently sees leaves that look bleached, but the veins are dark green. As the disease progresses, vines begin to decline, eventually collapsing and expos- ing fruit to the sun and potential sunburn. Damaged fruit also is more prone to other invaders such as mold. If cutting into the below-ground stem portion and crown tissue of infected plants, they may be necrotic, or dead, and “pretty ugly,” Aegerter said. Because foliar symptoms can be con- fused with tomato spotted wilt virus, southern blight or even potassium defi- ciency, Aegerter said it’s wise to have a lab- oratory confirm the field diagnosis. Vicky Boyd is a reporter in Modesto. She can be reached at agalert@cfbf.com.
high disease pressure. But varieties that have both FRD tolerance and the extended field-holding trait frequently produced the highest yields in the trials. UC and Ag Seeds publish their results annually in early winter so growers, pest control advisers and sales people can use them to make planting decisions for the upcoming season. In addition, Lopez said it was important to relay the data to seed breeders as they develop new varieties. To reduce the amount of inoculum in the soil, UC experts recommend rotating to nonhost plants for one or more seasons. UC Davis doctoral student Myles Collinson conducted laboratory and field trials over three years to determine the pathogens’ host range. Of the commonly grown crops, potatoes, peppers, cilantro, carrots and some sun- flower varieties yielded severe symptoms. Garlic, onions, alfalfa, corn, cotton, mel- ons, wheat and barley, on the other hand, were nonhosts. Sanitizing equipment before moving from one field to another is another man- agement tool to help reduce pathogen spread, Aegerter and Lazicki said. While removing all dirt and plant debris on ma- chinery may not be feasible, they said min- imizing the amount of plant debris using high-pressure air or water goes a long way. Equipment sanitation also is
Field trials have found that processing tomato varieties with fusarium stem rot and decline tolerance and the extended field-holding trait produced the highest yields under high disease pressure.
helpful to reduce the spread of broomrape, a yield-robbing processing tomato parasite found in the southern Sacramento Valley. As part of a federally funded specialty crop research project in 2025, Lazicki ex- amined the efficacy of K-Pam soil fumigant at 25 gallons per acre, 2.5 tons per acre of poultry manure and Trichoderma benefi- cial microbes used alone or together. She planted a tolerant variety and compared the treatments to untreated controls in a grower’s heavily infested field. Incorporating poultry manure following
K-Pam fumigation increased yields by 14.3 tons per acre compared to the untreated control and by 9.3 tons per acre compared to K-Pam alone, Lazicki said. Using the 2025 processing tomato price of $109 per ton, she said the K-Pam plus manure treatment yielded a $1,021 per-acre net profit over the untreated check. K-Pam plus manure produced a $776 per-acre return compared to K-Pam alone. “Fumigation and manure were both helpful even though it was a pretty tolerant
August 5, 2026 Ag Alert 11
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