Preharvest citrus fruit drop has been a concern for Florida citrus growers for the past few harvest years, and it’s no surprise that there is a connection to citrus greening, also known as HLB, exacerbating the problem. A recent article by UF/IFAS researchers shared all of the current knowledge concerning preharvest fruit drop based on recent studies, and it maintained that citrus greening-connected fruit drop can claim up to 60 percent of a crop, depending upon the severity of the disease, the tree cultivar, and other environmental factors. Unfortunately, researchers do not yet know why citrus greening increases fruit drop, but they did share all of the current knowledge to date on combating it.
Preharvest Fruit Drop Related to Citrus Greening
The bottom line of the research shows that citrus greening makes summer fruit drop worse due to limiting carbohydrate, nutrient, and water supply to the fruit, and through hormonal imbalances. Recommendations for reducing preharvest fruit drop include:
Maintain a constant water supply through irrigation. Watering once with a high volume allows water to leach away from the HLB-affected root system. Citrus growers should be watering frequently with small amounts of water so the trees get all they need.
Reduce transpiration. In hot weather, citrus trees lose water through their leaves’ pores during transpiration. In one study, citrus greening-free trees were treated with materials such as kaolin and calcium carbonate. The resulting improvement in water relations and photosynthesis resulted in an increase of 80 pounds or more of fruit per tree and a reduction in preharvest fruit drop.
Use plant growth regulators. Researchers maintained that tests of foliar applications of gibberellic acid on Valencia in the fall and early winter showed promising results for fruit drop in trees infected with citrus greening.
In short, researchers recommended that citrus growers pay close attention to the care of their trees and utilize an intensive nutrition and irrigation management plan during the growing season. Similarly, research into gibberellic acid is ongoing and may provide additional options for combating preharvest citrus fruit drop.
While researchers are still focused on finding a cure or treatment for citrus greening, they are also working on mitigating the effects of the disease—such as exacerbating fruit drop—to aid Florida citrus growers.