Last week, the California Citrus Quality Council sent out the following advisory to inform the industry about complying with export protocols for China and Korea.
China
Growers in San Luis Obispo (District 2) and Fresno Co. (District 1) should plan on a second application of either copper or an approved alternative to acreage destined for export to China by Jan. 21, 2025. Based on the Phytophthora-forecasting model, risk levels for San Luis Obispo Co. (SLO) are currently approaching level 3, whereas Fresno Co. is at a 2 for developing Phytophthora brown rot caused by Phytophthora syringae. Total precipitation is over 60 mm and copper reduction in these two counties is at 57.7 percent and 57.1 percent, respectively, based on total precipitation using the copper reduction model. The 14-day forecast predicts rain on Dec. 27 for San Luis Obispo and Fresno Counties, so these counties are expected to reach the red category following the next rain event.
The P. syringae risk levels for Imperial, E./W. Riverside, Ventura, Santa Barbara, San Diego Co., Kern, and Tulare Co. are at 1, and copper reduction is currently at 49.3 percent or less for these counties, indicating that these counties are not at risk at this time. The 14-day forecast starting on Christmas Day is for low rainfall for the Central Valley (District 1), southern counties of the Inland Empire, most southern Coastal regions (District 2), and desert regions (District 3). If additional rain occurs later in January, a second application may have to be planned for early to mid-Feb.
For all counties or regions, copper applications are required for the first preharvest foliar application between Oct. 15 and Nov. 30 to meet the China protocol, but the second treatment may be applied using copper, phosphite (ProPhyt and other products), oxathiapiprolin (Orondis older label), mandipropamid (Revus), or the premixture of oxathiapiprolin + mandipropamid (Orondis Ultra) based on environmental conditions. Oxathiapiprolin is the most active fungicide, providing long-lasting residual protection against Phytophthora brown rot. Additional advisories will be distributed if more fungicide applications are needed.
Korea
Due to the low number of accumulated hours of temperatures of less than -1°C and low precipitation levels in most counties of all districts, the risk for Septoria spot is currently very low (0) to low (1). Growers in San Luis Obispo and Fresno Counties are at a low risk level of 1 and should be prepared to make a second fungicide application once additional rainfall occurs. Because the accumulated hours of favorable temperatures are low, the potential for ice mark injuries to fruit is low. Infections, however, can still occur on other types of injuries such as wind scarring, especially when high levels of Septoria inoculum develop during high-rainfall conditions. Levels of Septoria spot were low last season (winter and spring of 2024), therefore, high rainfall will be required in winter of 2025 to increase inoculum levels.
For all counties or regions, copper or approved alternative fungicides such as Quadris Top, Luna Sensation, Priaxor and Cevya can be used for acreage destined for export to Korea once the risk reaches level 3 (red) according to the Septoria environmental model. More rain is forecasted on Christmas Eve for Fresno Co. and San Luis Obispo Co., but in the next 14 days, there should be low rainfall for all other citrus producing counties. In general, additional precipitation of >90 mm (3.5 inches) is needed before the risk for Septoria spot reaches an actionable level.
The GAPs for Septoria and Phytophthora management include more detailed information. Follow-up advisories will be distributed in the coming weeks if additional fungicide applications are needed for Septoria and Phytophthora brown rot.
China and Korea Acreage
If citrus groves are being managed jointly to meet the China and Korean protocols, an application of copper or a copper alternative is needed to maintain eligibility for both export markets for Fresno and San Luis Obispo. Fungicides listed for Phytophthora brown rot can be mixed with fungicides listed for Septoria Spot.
Additional Information
Dr. J. E. Adaskaveg at UC Riverside is monitoring environmental conditions and is modeling disease risk for all citrus growing regions in the state. He is also monitoring 14-day forecasts and actual weather conditions to determine if additional applications are necessary in citrus growing counties and regions across the state in the coming weeks.
Please contact Jim Cranney at (530) 885-1894 or jcranney@ccqc.org if you have questions or need additional information.
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