University of Florida Institute of Food and Agricultural Sciences researchers Megan Dewdney, Mark Ritenour, Liliana Cano, Eva Mulandesa and Monty Myers recently provided an update of their greasy-green disorder research. Excerpts follow from the Indian River Citrus League’s River Ramblings publication:
“Greasy green” is a term applied to fruit that develop what appears to be greasy spot rind blotch symptoms (Zasmidium citri-griseum). The symptoms often start appearing in November where there are few to no greasy spot symptoms on the leaves.
A project began in April 2022 to understand what might be causing this disorder and to develop ways to mitigate it. Field trials were conducted to determine whether the flush cycle and infection period for Z. citri-griseum have changed due to the influence of HLB. A site located in Fort Pierce was selected. Two blocks with different grapefruit varieties were monitored.
A total of 1,200 leaf discs obtained from leaves were evaluated and suggested that the epiphytic growth on leaves started in June on both varieties, as reported in previous studies. When the trees were sampled, there were very few symptomatic leaves present in the grove. However, greasy-green symptoms were present on the fruit.
Studies suggest that epiphytic growth started in September on both white and red grapefruit, which was unexpected.
The data suggests the organism responsible for greasy spot is involved with greasy-green symptoms on fruit, even though greasy spot is not observed on the leaves. It appears that the organism can reproduce in the leaf litter, despite the suppression of lesions by chemical control.
A pesticide trial was conducted in 2022, and the data were collected in 2023. Multiple commercial pesticides were tested for efficacy against greasy green/rind blotch.
For disease suppression and greatest percent of marketable fruit, Double Nickel LC, Cohere and Kocide 3000-O and Enable alternated with Kocide 3000-O had significantly greater performance. Other promising products included Miravis Top, other Double Nickel LC and Kocide 3000-O treatments, Oxidate with Cohere, and three applications of G304 and K22. This is only one year of data.
Researchers evaluated red and white grapefruit from greasy-green affected blocks in January after initial degreening treatment in December. The treatments included degreening and cold treatment.
Degreening (with or without a cold treatment) significantly improved peel color after five days. However, even the best-performing treatment was not acceptable.
In February, researchers again evaluated color development of greasy-green affected red and white grapefruit after different lengths of degreening. While degreening again improved color compared to the control, even after 20 days ambient storage, peel color was still not acceptable. Thus, reliable means of coloring greasy-green affected fruit after harvest are still elusive.
Source: Indian River Citrus League
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