Jaime Ott, UCCE Tehama, Shasta, Glenn, and Butte Counties

Bacterial blast, caused by Pseudomonas syringae pv. syringae, can be devastating to almond yields in years where cold, wet weather coincides with almond bloom. Grower reports of past crop loss supported a Section 18 emergency request for the use of Kasumin® 2L (active ingredient kasugamycin) on almonds during bloom, which has been approved by DPR and EPA ONLY during the 2024 bloom season (Feb 2-Apr 15).

The Section 18 Emergency Use Authorization for Kasumin® 2L  applies to counties where crop loss data has been reported: Butte, Calaveras, Colusa, Contra Costa, Fresno, Glenn, Madera, Merced, Placer, San Joaquin, Stanislaus, Sutter, Tehama, Yolo, and Yuba counties. This emergency approval allows for up to two applications of Kasumin® 2L for bacterial blast before petal fall when wet, near-freezing or freezing conditions are predicted. Kasumin® 2L can be applied only from the ground by airblast sprayer and should be used at a rate of 64 fluid ounces (0.084 pounds of active ingredient) in at least 100 gallons of water per acre. If you are interested in using Kasumin® 2L during bloom, please contact your local Agricultural Commissioner’s office, talk with your PCA, and carefully follow the label; the label is the law.

Pseudomonas syringae pv. syringae is ubiquitous in orchards, so bacterial blast can develop whenever environmental conditions are right (freezing or near-freezing and wet). In the past, copper sprays were used to protect trees from bacterial blast. However, copper resistance is common in P. syringae populations throughout the state, and in many orchards copper sprays are no longer effective for controlling bacterial blast. Kasumin® 2L has been shown to be effective, and there is no documented resistance to kasugamycin in P. syringae, but the material is expensive. Given tight farming budgets, growers and PCAs will have to weigh disease risk against the anticipated cost-benefit of employing Kasumin® 2L.

For more information, check out the many articles on bacterial blast at sacvalleyorchards.com.

Please note: mention of a pesticide does not constitute a pesticide recommendation.