Learning about Greasy Spot within the Citrus Under Protective Screen Production System
Posted August 2025
Researchers: Megan Dewdney, Lauren Diepenbrock
Contact: Megan Dewdney, UF/IFAS CREC mmdewdney@ufl.edu
Summary:
The citrus under protective screen (CUPS) system has allowed for the ability to produce high-quality fresh fruit in areas that are afflicted by huanglongbing (HLB). The most common type of citrus currently being produced in CUPS is grapefruit. Grapefruit is notorious for being highly susceptible to many foliar diseases and being within the CUPS environment has not changed this. Greasy spot is the most troublesome of the foliar diseases within the CUPS system so far. It can cause damage to the fruit rind, lowering packout, but most importantly leaf symptoms can cause premature leaf drop and yield reduction. To understand where spores are coming from and when, we have been spore trapping within CUPS structures. To date, we have found that more spores are found near the walls of CUPS compared to the middle, although there are enough spores to cause disease in either location, implying many spores are passing through the screen into the structures. We have observed that the majority spores eject from 4 am to 12 pm. This is likely because of the morning irrigation cycle and wetting from dew leaving a film of water on the leaf litter where the spores are formed. This may mean that inoculum reduction strategies like accelerated leaf litter decomposition may be minimally effective if there are nearby groves that can be inoculum sources. However, leaf litter management still needs to be tested to show whether there would be a sufficient disease reduction for it to be an economically viable management practice.
Take Home Message:
- Greasy spot can reduce yields even in a CUPS environment.
- The fungal spores can easily enter a CUPS structure, leading to infection regardless of practices with an operation.
- Greasy spot management programs in CUPS may need to consider the management occurring in surrounding groves.
