Florida’s rainy summer season is prime time for root rot, but it’s also the time that brown rot rears its ugly head. A UF/IFAS Tip of the Week shared that there have been high soil Phytophthora propagule counts, the organisms that cause brown rot, reported so far this year, in Southwest Florida especially. The UF/IFAS information was also clear that brown rot can cause total yield loss. Thankfully, the folks at UF/IFAS also had some pointers for managing brown rot in your Florida citrus grove this summer.
Tips for Brown Rot Management
Brown rot causes leathery lesions that are tan to olive brown on the fruit rind, causing fruit drop and fruit that can no longer be sold.
According to UF/IFAS, both Phytophthora palmivora and Phytophthora nicotianae can cause brown rot, but P. palmivora is the greater concern because it can travel via rainwater splashes from fruit to fruit throughout the tree while P. nicotianae is a problem on unskirted trees affecting the lower third of a tree’s canopy. Accordingly, it’s important to know which forms of Phytophthora are present in your grove to decide the level of “management aggressiveness.”
Additionally, some citrus varieties are becoming more susceptible to brown rot, such as grapefruit and early sweet orange varieties like Hamlin. Since most grapefruit trees receive copper treatments for citrus canker through June, they are usually protected as copper also targets Phytophthora. However, UF/IFAS maintains that Hamlin trees usually no longer receive copper treatments for citrus canker after June, leaving them exposed to Phytophthora. UF/IFAS maintained that many Hamlin growers saw total yield loss due to brown rot last year.
Tips on protecting your grove from brown rot include:
- An application of phosphite, applied before infection is detected, will provide the best protection against brown rot. This application is usually done in July, so you should consider it if your groves were not treated last month.
- One application of phosphite should offer enough control through a normal rainy season, but if the rainy season extends into September or October, citrus growers should consider another phosphite application to keep brown rot at bay.
- Copper can be used as a treatment to protect healthy fruit if brown rot has already affected some fruit in the tree. It should be reapplied every 21 days to offer the best control of brown rot.
- The Revus Fungicide label was expanded recently to be used as a foliar spray in treating brown rot, and claims it offers some control up to 30 days. However, this mode of action has not yet been studied and tested.
This column is sponsored by Griffin Fertilizer Co., and the opinions expressed herein may not reflect those of CFAN or of its advertisers.
BIO: Mike Roberts is the vice president of the Frostproof, Florida-based Griffin Fertilizer Co. Roberts joined the company in November 2011. He has spent the majority of his career in the fertilizer and ag-chem industry. Roberts earned a Bachelor of Science degree in citrus production from Florida SOuthern College in Lakeland. For more information, visit GriffinFertilizer.com.