Postbloom Fruit Drop
Pathogen
- The fungus Colletotrichum acutatum
Flower Symptoms
- Flowers can be infected within 24 hours and symptoms appear in 4 to 5 days
- Peach to reddish brown necrotic spots on petals
- Diseased petals are dark brown to orange and dry first in the affected areas
- Petals shrivel and drop from PFD-affected flowers
- Buttons or persistent calyxes
- These are the floral disks, where the fruitlets have fallen
- They are very difficult to detach from the trees, requiring significant force
Leaf Symptoms
- Leaf twisting around affected flower clusters
Varieties Affected
- Affects all species and cultivars of citrus, but severity varies according to time of bloom and rainfall
- Navel and Valencia oranges have experienced the most damage in Florida
- Grapefruit have the least damage
Increased Risk Factors
- Cultivars with multiple bloom periods like Navel
- Declining trees (HLB, blight, Phytophthora, etc.) with extended or off-season bloom
- PFD in a block in the last 5 years
- PFD on early bloom throughout the grove
- Rainfall in the last 5 days during bloom
Management
- Groves with persistent calyxes (buttons) from the previous year should be closely examined once bloom begins
- If infected flowers are present on scattered early bloom, the Citrus Advisory System recommendations should be followed once sufficient bloom is present
- Groves with a history of PFD should be checked twice weekly during the bloom period
- Unhealthy citrus trees (HLB, blight, or Phytophthora) should be removed where possible because off-season blooms may provide a site for fungal spore buildup
Spray Timing
A fungicide application is recommended if these three criteria are met:
- Sufficient bloom is present or developing and represents an economically significant portion of the total crop.
- No fungicide application has been made in the last 7 to 10 days.
- The Citrus Advisory System recommends an application.
Resources
- Commercial grove management practices are reviewed and updated annually in the Florida Citrus Production Guide.
- The Quick Reference Guide to Foliar Fungicides is updated annually and available as a downloadable PDF.
- Fungicide application decision support system, Citrus Advisory System
