The California Citrus Quality Council (CCQC) is contacting the industry to provide information on how to comply with the China and Korea export protocols. Due to recent high precipitation and predicted high precipitation in the coming days, this updated announcement is warranted.
Previously, growers in coastal regions of District 2 including Ventura, Santa Barbara, San Luis Obispo, San Diego, and W. Riverside were informed that a second application should be made by Jan. 21, 2024. Currently growers in Fresno, Tulare, Kern, E. Riverside, Counties should make a second application of either copper or an approved alternative to acreage destined for export to China by Feb. 22, 2024. The Phytophthora-forecasting model which is based on accumulated wetness periods and favorable temperatures was used to predict the risk for developing Phytophthora brown rot caused by Phytophthora syringae, and additionally, the high anticipated rainfall in the coming days was also taken into consideration. These predictions resulted in the highest risk level of 3 in the regions indicated (Table 1). Additionally, copper reduction that is calculated based on total precipitation using the copper reduction model is at over 80%, except for Tulare Co. where it is currently at 58.6% (with anticipated rainfall expected to result in higher reduction) (Table 1). Although the P. syringae risk level for East Riverside Co. is at 2, the copper reduction risk is at level 4, indicating that a second fungicide application should also be made in this county. Only Imperial Co. is currently at a low risk for P. syringae infection, and a second application is not immediately needed.
For all counties or regions, copper applications are required for the first preharvest application between Oct. 15 and Nov. 30 to meet the China protocol, but the second application may be done 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 more fungicide applications are needed.
Growers in Santa Barbara and San Luis Obispo Co., where rainfall was high, were previously advised that they are at high-risk (level of 4 or 3) and should make a second fungicide application by Feb. 4, 2024. As of this forecast, we had enough rainfall to remove copper residues from fruit and a second application is advised for all counties except for Imperial Co. Due to the low number of accumulated hours of temperatures <-1C and moderate precipitation levels in most remaining counties except San Diego Co., the risk for Septoria spot is currently low (Table 1). Infections, however, can still occur on other types of injuries (e.g., wind scarring) especially when elevated levels of Septoria inoculum develop under accumulated rainfall. Therefore, with additional forecasted rain there is a risk for Septoria spot to develop on unprotected fruit with low copper residues. Therefore, a second fungicide application is advised by Feb. 22, 2024, for all counties except Imperial.
For all counties or regions, copper or approved alternative fungicides (e.g., Quadris Top, Luna Sensation, Priaxor) can be used for acreage destined for export to Korea. Abound is being phased out in the future and is replaced with a 2ee for Quadris for managing Septoria spot. More rain is forecasted in the coming days and weeks and thus, growers and PCAs should plan to manage Septoria spot with a second fungicide application in the next three weeks.
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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.