Luke Milliron, UCCE Orchard Advisor, Butte, Tehama & Glenn Counties;
Phoebe Gordon, UCCE Orchard Advisor Madera and Merced Counties

Bacterial blast (Pseudomonas syringe), although thankfully not a problem every year (hopefully including 2021), can be tremendously damaging to almond yields. For example, significant crop damage was reported in the Sacramento Valley in 2017 and 2018, and in the San Joaquin Valley in 2017 and 2019. These grower reports of past crop loss supported a Section 18 emergency request for the use of kasugamycin on almonds during bloom.

The EPA approved this emergency request for kasugamycin (Kasumin 2L) use during the 2021 bloom season ONLY for February 12 through petal fall. The request was granted for select counties that had supplied crop loss data, these counties included Yolo, Sutter, Yuba, Colusa, Glenn, Butte, and Tehama in the Sacramento Valley as well as San Joaquin, Stanislaus, Merced, Madera, and Fresno in the San Joaquin Valley. This emergency approval allows for use of kasugamycin for bacterial blast when cold or freezing conditions are expected at a use rate of 64 fluid ounces per acre. If you are interested in using kasugamycin during bloom, please contact your local Agricultural Commissioner’s office and carefully follow the label, label is law.

In past years, some almond growers have reported 20-40% crop losses, in part due to blast. For example, bacterial blast hit some varieties in the Regional Almond Variety Trials in Butte and Madera Counties in 2017 and 2019. The bacteria P. syringae which can cause both blast and canker is ubiquitous on surfaces in our orchards, however it only causes infections under the right conditions. The right conditions for bacterial blast and canker are wet and cold (e.g. frost). These conditions stress the tree and make them more vulnerable to infection, as is the case for bacterial canker, which is a different expression of the same infection. For example, in 2017, the Regional Almond Variety Trial at CSUC experienced four nights below 30ᵒF coinciding with full bloom and significant damage was observed (photo 1). Copper has been the only main control measure for this disease, however copper resistance in P. syringae is widespread and copper sprays are believed to be mostly ineffective at controlling this pathogen.

In a recent episode on Growing the Valley podcast, Jim Adaskaveg gives an update on bacterial blast management, including the efficacy of kasugamycin.

Mention of a pesticide does not constitute a pesticide recommendation. Special thanks to Dr. Jim Adaskaveg who wrote the Section 18 request, to Elaine Trevino and the Almond Alliance who submitted the request to DPR, and to the Central Valley almond growers who supplied crop loss data.

Photo 1. Bacterial blast damage in almond at the northern Regional Almond Variety Trial site at California State University, Chico in 2017 (photo by Dani Lightle).