Mike Roberts

Scouting for Postbloom Fruit Drop

Postbloom fruit drop (PFD) has not been a huge issue in Florida citrus groves since 2016, but a recent UF/IFAS Tip of the Week maintained that conditions were favorable in late 2021 and that PFD buttons, or persistent calyces, were observed in groves in 2022 before the weather turned cold. Essentially, this means that the fungal inoculum is present and growing. If weather conditions turn favorable, then a PFD outbreak could develop quickly. As a result, it’s time for Florida citrus growers to start scouting for postbloom fruit drop.

Know The Optimal Conditions 

Postbloom fruit drop is mainly caused by the fungus Colletotrichum acutatum. The fungus is always present in Florida citrus groves, but it needs favorable weather conditions to grow and infect a tree’s flowers. The ideal weather conditions are temperatures between 72 and 79 degrees and periods of leaf wetness of more than 16 hours—usually from rain. However, Longer periods of leaf wetness amid cooler or warmer temperatures can also lead to infection.

 

Florida citrus growers should pay attention to the Citrus Advisory System, which identifies if there is an increased risk of PFD in your area during the main bloom.

 

Scouting for PFD Symptoms 

PFD symptoms can be tricky to spot before the major bloom period, but it’s important to know if your grove has a PFD infection brewing because the fungus can spread quickly during optimal weather conditions. Tips for scouting for PFD include:

  • Scout early on popcorn and opened flowers because they are the most susceptible to the disease. 
  • Look for peach to pinkish brown lesions on flower petals.
  • When conditions are ideal for PFD, whole flower clusters will show lesions.
  • PFD-affected flowers turn into fruitlets that will become chlorotic and fall off.
  • Fallen fruitlets leave behind PFD buttons, or persistent calyces, that are hard to remove.
  • Naturally falling fruit will also leave behind buttons, but the difference is these buttons are easy to remove.

If you know you have symptoms of PFD in your grove, or you grow a highly susceptible cultivar, like Navel or Valencia, then you can start treatment before weather conditions become ideal and PFD gets out of hand.