Greasy Green and Its Management

A citrus disorder called greasy green has plagued Florida grapefruit producers for several years, causing a significant reduction in profits. University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Associate Professor and Extension Specialist Megan Dewdney discussed the disorder and its management at the Citrus & Specialty Crop Expo in August. Dewdney works at the UF/IFAS Citrus Research and Education Center. 

Dewdney called greasy green a disorder where fruit, particularly grapefruit, remain green despite degreening treatments. It occurs early in the season — in November or December — and causes fresh fruit growers and packers losses of from $20,000 to $1.7 million a year. So far, the disorder has not been reported in citrus under protective screen (CUPS).

The suspected cause of greasy green is the same fungus that causes greasy spot/rind blotch, Dewdney stated.

According to Dewdney, suspected fungicide resistance may contribute to insufficient management. She said greasy green cannot be resolved with post-harvest measures and needs to be managed in the grove. Dewdney offered these management suggestions:

• A greasy spot program should be a priority.
• Full coverage of the canopy is important, particularly the underside of leaves.
• Slow tractor and increase water.
• Copper rates adequate for canker suppression may not be enough for greasy green/greasy spot.
• Increase rates in May and June.
• Copper can cause burn in high May temperatures (> 94°F).
• Timing may need to shift to earlier in May.
• Ensure fungicide programs are not relying on a single mode of action.
• Rotation is very important.
• An August application may be needed in difficult blocks.

Dewdney’s take-home messages stated that:

• Greasy green disorder causes fresh fruit producers significant losses.
• Symptoms resemble greasy spot/rind blotch on fruit and start early in the season.
• No symptoms are observed on leaves.

Greasy green should be treated as a form of greasy spot, Dewdney concluded.

See the full Expo presentation here.