What is Causing that Greasy Green Color on my Grapefruit?
Posted August 2025
Researchers: Megan Dewdney, Mark Ritenour, Liliana Cano
Contact: Megan Dewdney, UF/IFAS CREC mmdewdney@ufl.edu
Summary:
In the last five years, 89% of grapefruit growers have struggled with a disorder that they refer to as greasy-green, leading to losses between $20,000 to $1.7 million per year. The disorder causes the fruit to have large, diffuse green patches on the rind after degreening, making it no longer suitable for the fresh market. The disorder visually resembles rind blotch, caused by the fungus Zasmidium citri-griseum (formerly known as Mycosphaerella citri), but there are nearly no symptoms on leaves. The cause of greasy-green remains unclear, but in Spring 2022, UF/IFAS started a project to determine if the epiphytic growth of Z. citri-griseum was different, possibly in response to changes in the host caused by huanglongbing (HLB), a warmer environment, or cultural practices. From leaf samples, despite there being no disease symptoms on the leaves in the grove, epiphytic (plant surface) growth started in May and June. There were symptoms on the fruit. Post-harvest degreening trials were conducted. While degreening, with or without 24 hours at 38 °F, significantly improved peel color compared to just 38 °F or no treatment, a green color remained. In addition, when samples were taken from fruit, there was more epiphytic growth on fruit with symptoms than asymptomatic fruit and the increased intensity of the symptoms corresponded with greater epiphytic growth. Confirmation studies are on-going to ensure our conclusions are correct.
Take Home Message:
- Despite leaf symptoms of greasy spot not being visible, we can detect Z. citri-griseum growth on the leaf surfaces.
- On fruit with severe greasy green, we observe more Z. citri-griseum spores and surface growth.
- Post-harvest degreening has not reduced the greasy green symptoms on affected fruit.
