Protect Citrus Trees From Heat Stress

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heat stress
Fruit drop can be a sign of heat stress.

By Amir Rezazadeh

Heat stress affects the production of different citrus varieties, particularly seedless varieties. The severe effect of heat stress can be seen during the flowering and fruit set stage as well as June drop. High temperature can affect different growth stages of citrus trees, such as vegetative growth, flowering and fruit set.

The following are early signs of heat stress on citrus trees:

  • Wilted leaves
  • Leaves turn yellow.
  • Green leaves start falling off the trees.
  • Leaf edge curl
  • Fruit drop may occur.

One of the strategies that helps trees to tolerate midday high temperatures is to irrigate early in the morning or during evening to reduce evaporation loss. In summertime, newly planted trees should be watered consistently and more frequently because they do not have a fully established root system. More frequent watering helps trees to better absorb the water and to prevent drought stress. A sprinkler or drip system is a good way to ensure consistent watering. Citrus trees planted in sandy soils need more water compared to those planted in heavy soil.

Check the soil moisture level. If the soil is dry, start irrigation as soon as possible. Some effects of heat stress may last longer or even appear later. It is highly recommended to provide adequate water for trees during hot days.

Using mulch around the base of the tree helps to retain soil moisture. This is especially important for young trees with root systems established around the soil surface. Mulch should be spread in a 2- to 3-foot diameter around the tree. It is important to leave a space between the tree’s trunk and the mulch to prevent rotting.

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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