Explore the conclusions derived from a UF/IFAS study looking at how citrus greening affects preharvest fruit drop.

Citrus greening has many ways of negatively affecting yield, and preharvest fruit drop is one of them. According to a Citrus Industry article on the study, citrus greening can cause an increase in a citrus tree’s mature fruit drop rate up to three months before harvest time. See the takeaways from the study below.

Talking Points from the Preharvest Fruit Drop Study

The study used both early-season Hamlin and late-season Valencia sweet oranges, comparing trees showing three different levels of citrus greening symptoms. Trees were rated by both visual judgement and measuring the tree’s photosynthetically active radiation (PAR) level—or the density of the tree’s canopy–as showing mild, moderate, or severe symptoms.

Takeaways from the study include:

  • “Total fruit drop rate was correlated with HLB severity and canopy density.”
  • Both Hamlins and Valencias with severe symptoms of citrus greening had a greater preharvest fruit drop than those with moderate or mild symptoms.
  • Both Hamlins and Valencias with severe symptoms has smaller sized fruit.
  • Overall, fruit that remained attached through harvest were larger in size than fruit that dropped prematurely, and measurement of fruit detachment force (FDF), showed that smaller fruit was more prone to dropping.
  • “It is likely that HLB restrains fruit growth during early developmental stages, which leads to a high inclination for fruit drop at maturity.”
  • Adequate water supply during stage II of fruit development is “critical to ensure uninterrupted fruit development and growth for better fruit retention.”
  • Stress conditions, like drought, likely exacerbate preharvest fruit drop.
  • “Carbohydrate levels in fruit are independent of HLB severity or the tendency of fruit drop.”

Per the article, researchers maintain that the study demonstrates a “clear relationship between HLB severity, fruit size and preharvest fruit drop,” and that tree health is key. They recommend an adequate nutritional program, optimal irrigation, and avoidance of stress conditions.