While you may be watering periodically when it hasn't rained and the potting mix may feel moist, the trees are not getting sufficient moisture to continue maturing the fruit while maintaining their vigour.ĭuring hot weather, potting mix even in large pots will become quite warm and this too inhibits moisture uptake and increases evaporation from the potting mix. If citrus trees are otherwise healthy, with green foliage, flowers and plenty of fruit ripening, then the most common cause of leaf curl is lack of moisture. Always use a citrus fertiliser that includes boosted magnesium and iron to assist leaf greening and strength. A thorough application of white, eco or horticultural oil over upper and lower leaf surfaces and the bark may prove beneficial - it certainly won't cause any harm.Ĭonsider your feeding regime too. IsobelĬheck also for insect pests, especially on the undersides of the leaves. If it is citrus leaf miner, a moth that lays eggs in the leaves, the leaves will be quite deformed. Individual protective covers and kaolin particle films shade young trees and help keep them cool.If the leaves look pretty green and healthy the tree probably just needs more regular watering. Yes, young trees are more sensitive to heat than mature trees due to a shallower root system and less storage capacity in the trunk. Any treatment that shades the tree will help prevent heat stress. Avoid using any spray with oil in it as oil on leaf surfaces is damaging in summer heat. Therefore, maintain a steady mineral nutrient supply throughout the summer. HLB-affected trees may be highly sensitive to heat due to poor root systems and chronic nutrient deficiencies. Groves with row middles with good soil cover from cover crops or turf can stay much cooler than bare soil. Reducing competition from weeds can also prevent competition for water. Frequent irrigation is recommended to meet extra water demand. There are multiple strategies that growers can take. However, heat reduces photosynthesis long before any visible signs occur.Īt the Citrus Research and Education Center, researchers have observed several benefits of (a) partial shading and (b) kaolin clay applications on canopy growth during summer and post-summer yield. If timely care is not taken, leaf bleaching and rapid yellowing of canopy, growth retardation, reduction in flowering and fruit setting, increased fruit drop, and fruit sunburn can occur. Yes, inward curling of leaf edges is an early sign of heat stress. But citrus leaves heat above air temperature and can even reach110 degrees and higher on hot days.ĭo citrus trees show signs and symptoms of heat stress? If leaf temperature frequently hits 98 degrees, trees could start feeling mild heat stress. What temperature is stressful for citrus? The red arrows indicate curled leaves in an HLB-affected Valencia tree on a hot sunny day in June. Citrus leaves can curl up as a reaction to heat and less water content. Also, high soil evaporation, irregular rainfall and poor soil water-holding capacity can often lead to summer drought and make trees more vulnerable to heat. Long, hot, oppressive summer days can heat up leaves and fruit and make the trees extra thirsty. In Florida, the hot season lasts more than four months. Heat stress could take a toll on citrus tree health and fruit yield.
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