The Environmental Protection Agency (EPA) California Department of Pesticide Regulation (DPR) have issued a Section 18 emergency use exemption for the use of Kasumin 2L to control bacterial blast in almonds that was requested by the Almond Alliance of California. The exemption is effective February 1 through April 15, 2022 for the counties of Butte, Colusa, Fresno, Glenn, Madera, Merced, San Joaquin, Stanislaus, Sutter, Tehama, Yolo and Yuba. The Section 18 was initially granted in 2020 and the full Section 3 registration is pending in 2022.
The bactericide acts mainly as a preventative and is applied to coincide with early shoot emergence and bloom to provide a protective layer of the bactericide on emerging green tissue and blossoms.
Under the Section 18 approval, Kasumin can be applied up to two times at a use rate of 64 fluid ounces per acre in tank mix or rotation with other fungicides. The application should be made preventatively when conditions favor disease development from bud break to petal fall. Application is not allowed five weeks after petal fall (mid-April.)
This bactericide is the lone member of FRAC Group 24 and is therefore effective as part of a rotation program with other bactericides for multiple bacterial diseases. The product has a 12-hour restricted entry and a 100-day pre-harvest interval. It provides good preventative activity and has no cross resistance with copper or other fungicides/bacgtericides where some resistance may exist.
UC Riverside Plant Pathologist Jim Adaskaveg said outbreaks of bacterial blast are caused by the bacteria Pseudomonas syringae and usually show up in spring following cold wet conditions. The bacteria colonize plant tissue after injuries occur from frost. Bacterial blast was found in 2019 to be most severe in varieties of almond that bloom during cold weather. Growers should be following frost alerts and using cultural practices such as irrigation or wind machines to lessen the effects of frost while using kasugamycin as a preventative treatment. Kasumin can be applied 7 days prior to frost forecasts to minimize the population levels of the epiphytic bacterial pathogen, Adaskaveg said. Kasumin provides a unique mode of action with effectiveness on both bacterial blast and bacterial spot. However, bacterial spot is favored under warm wet conditions.
Blast infections of dormant buds result in bud death, and it can be confused with brown rot. Blossoms may wither suddenly and turn dark brown. When there are multiple blasted flowers, the shoot tip may become necrotic and exude gum.
“Like most of these diseases, you get an infection and then you see symptoms a week or two later,” Adaskaveg said.
Blast infections are most severe in the lower part of the tree canopy and in low places in an orchard where colder air has settled. Growers who experienced previous bouts with this disease now know which varieties of almonds are most susceptible and orchard locations where trees are most vulnerable due to favorable environmental conditions.
