Have a question?

Tree Health :: Drought Stress Implication for MH


Reduced canopy size by hedging can improve water status until re-growth occurs and might improve efficiency of mechanical harvesting. Improved water relations should enhance the tree’s tolerance to other possible stresses including mechanical harvesting. In late season ‘Valencia’ harvesting trials, we are using drought stress from Dec until March to delay flowering for 3-4 weeks in the spring. There should be less abscission of younger smaller fruit in late season harvesting than of older larger green fruit in well watered trees.

The effect of drought stress on fruit detachment force (FDF) is also being evaluated with the abscission research team.


  • Determine if reduced canopy size by hedging improves tree water status until regrowth appears and perhaps improve stress tolerance.
  • Determine how drought stress can cause a delay in growth flush and flowering to aid in the ability to use mechanical harvesting later in the “Valencia’ harvesting season
  • Determine what effects drought stress has on fruit detachment force and if less intense mechanical harvesting can be employed.

Key Findings (Updated on 10/07)

  • The percentage of fruit removal by trunk shaking was improved in hedged trees. Properly adjusting tree size by hedging improves the percentage of fruit removal by mechanical harvesting and thus, compensates for the loss of fruit due to hedging in the previous fall.
  • We have learned that wintertime drought stress can delay ‘Valencia’ flowering in the spring. Although later flowering was not as intense as in well watered trees, previous drought stress had little effect on fruit set. Younger smaller fruit from previously droughted were not affected by mechanical harvesting in June. The later fruit growth appeared to catch up with well watered treatments. Fruit yield in 2008 will determine if the drought in 2007 affect total yield.
  • First evaluations have indicated that water stressed trees have a lower FDF than control trees when harvested early in the morning. This has implications on the effect of tree water status, rootstock, time of day and abscission chemical sprays on minimum required machine force for successful and safe mechanical harvesting.

Activities Planned for 2007-2008

  • Repeat delayed flowering and green fruit evaluations from controlled drought studies.
  • Develop greenhouse experiments to assess the physiological impact of partial root zone drying and deficit irrigation on citrus trees.
  • Continue drought stress effect studies on ‘Valencia’ fruit detachment force (FDF).
  • Set up an experiment to determine potential to control tree water relations using intercrops.

Publications and Extension Products


Melgar, J.C, J.P. Syvertsen and L.G. Albrigo. 2007. Growth flush and flowering is delayed by winter time drought stress in ‘Valencia’ orange trees. HortScience 42: (in press) ASHS Meetings, July 16, 2007, Scottsdale, AZ

Syvertsen, J.P. 2006. Citrus Harvesting and Utilization Effects on Production: An Introduction To Barriers and Opportunities. Symposium. Proc. FSHS 119: 198.

Li, K.-T, J.P. Syvertsen, and Jill Dunlop. 2006. Defoliation after Harvest with a Trunk Shaker Does Not Affect Canopy Light Interception in Orange Trees. Proc. FSHS 119: 187-189.

García-Sánchez, F., J.P. Syvertsen, P. Botía and J.G. Perez-Perez. 2007. Physiological Responses of Two Citrus Rootstock Seedlings to Flooding and Drought Stress. Physiologia Plantarum 130: 532–542.


Syvertsen, J.P. FL Citrus Growers Institute, 17 Apr 2007, Lake Alfred FL. Presented "Factors that affect citrus growth flush."

For more information:

Jim Syvertsen
Kelly Morgan
Bob Ebel

Visits since 05/21/2014