By Amir Rezazadeh
Rising temperatures and climate change challenges of recent years have brought a significant threat to citrus trees. Heat stress, caused by prolonged exposure to high temperatures, poses a severe risk to citrus trees. Excessive soil evaporation, inconsistent rainfall and poor soil water-holding capacity can make trees even more sensitive to heat.
High temperatures result in shortened internodes, injury to leaves, less flowers and fruit, fruit drop and smaller fruit. Early signs of heat stress on citrus include curled leaves, leaf and fruit drop, leaf bleaching and yellowing of canopy, growth slowdown, and fruit and leaf sunburn.
Watering in the early morning or in the evening to reduce transpiration loss helps trees tolerate the high temperatures of midday. Due to their immature root systems, newly planted trees should be watered more frequently during the summer. Citrus trees planted in sandy soils need more water compared to those planted in heavy soil.
More frequent irrigation enables trees to better absorb water and prevents drought stress. A sprinkler or drip system is an effective method for ensuring uniform irrigation.
Applying mulch at the tree’s base helps to retain soil moisture. This is particularly essential for young trees with root systems that are establishing near the soil’s surface. To prevent rotting, it is essential to allow space between the tree’s trunk and the mulch.
Nutrient-deficient trees may be more vulnerable to the negative effects of high temperatures. Maintaining healthy trees requires a constant fertilization schedule that spans the entire year.
Pruning should be avoided during periods of stress, as it may result in sun penetration into the interior of the branches and increase damage from heat.
Application of pesticides during the hottest part of the day should be avoided, as the chemicals can readily vaporize and cause leaf burning.
Amir Rezazadeh is a multi-county fruit and field crops Extension agent at the University of Florida Institute of Food and Agricultural Sciences St. Lucie County Extension office in Fort Pierce.
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