Growers should apply a second fungicide application of either copper or approved alternatives to acreage destined for export to China in Madera, Fresno, Tulare, Kern, Western Riverside, Ventura, Santa Barbara, San Luis Obispo, and San Diego Counties by Jan. 20, 2022. Risk levels in these counties are currently at the highest for developing Phytophthora brown rot caused by P. syringae based on the Phytophthora-forecasting model. These District 1 and 2 counties also have locations with 70 to 90 percent copper removal based on total precipitation using the copper reduction model. This is another indication that these counties should apply a second fungicide application.
A second application is not needed in District 3 counties of Imperial and eastern Riverside at this time. For all counties or regions, copper applications are required for the first application to meet the China protocol, but the second preharvest application may be conducted using copper, phosphite (ProPhyt and others), oxathiapiprolin (Orondis), mandipropamid (Revus), or the premixture of oxathiapiprolin + mandipropamid (Orondis Ultra) based on environmental conditions. Oxathiapiprolin is the most active fungicide and provides long-lasting residual protection against Phytophthora brown rot. Additional advisories will be made if additional fungicide applications are needed.
Growers should apply a second copper or approved alternative (Quadris Top, Luna Sensation, Priaxor) fungicide application to acreage destined for export to Korea in Ventura, Santa Barbara, and San Luis Obispo counties by Jan. 20, 2022. These counties are at level 4 (highest risk). Citrus groves in Madera, Fresno, Tulare, Kern, western Riverside, and San Diego counties are at Level 2 (yellow), whereas eastern Riverside and Imperial counties are at level zero according the Septoria environmental model. Applications are generally called for when Level 3 (red) is reached. High rainfall occurred in District 1, but temperatures below -1 did not accumulate. Therefore, the potential for ice mark injuries was low, but infections can still occur on other types of injuries. Additional rainfall in District 1 of approximately 0.5 to 1 inch (12-25 mm) will change the risk to level 3. An additional advisory will be made in the next few weeks if additional fungicide applications are needed for Septoria.
China and Korea Acreage
If citrus groves are being managed jointly to meet the China and Korean protocols, then an application of copper or a copper alternative is needed to maintain eligibility for both export markets for the counties listed above under “China”.
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 10-day forecasts and actual weather conditions to determine if additional applications are necessary in citrus growing counties/regions across the state in the coming weeks.
Please contact Jim Cranney at (530) 885-1894 or via e-mail at email@example.com if you have questions or need additional information.