Hurricane Recovery

Drainage

Establish Drainage. This is a very important first step. Roots require oxygen from the air and excess water displaces all the air in soil. When temperatures are over 75 o F, fibrous root death from lack of oxygen (anoxia) can begin within 7-14 days. As citrus roots die, trees develop water stress-like symptoms such as leaf wilting, yellowing and leaf drop.  How quickly water stress develops depends on water movement, soil pH and the amount of hydrogen sulfide present.  Moving water will delay the development of anoxic symptoms so it is important to start drainage operations as soon as possible. If drainage drops water levels 4-6 inches per day, root loss can be avoided. Even circulating water within a block is better than allowing water to stagnate. Hot weather will speed up the development of visible symptoms. Hydrogen sulfide (H 2 S) minerals produced by anaerobic bacteria have an odor of rotten eggs (in acid soils but not in all cases) and is an indication that fibrous roots are dying. This process can be slower at higher soil pH. Swingle and Carrizo rootstocks tend to tolerate flooding better than sour orange and Cleo. Although Swingle performs well on soils subject to periodic flooding, its resistance to Phytophthora root rot breaks down if the root system is weakened by water stress. After excess water has drained and if root damage has not been excessive, trees can begin recovery by regenerating fibrous roots and re-establishing the balance between roots and shoots. This tree recovery process requires good irrigation and fertilizer management while new roots grow.  Light, frequent split applications of both water and nutrients would be beneficial. If there is no rain and the soil is not saturated, irrigation for a few hours 2 or 3 times per week would be sufficient to promote root growth. If there is prolonged visible wilt, tree survival may be improved by reducing canopy volume by hedging, topping or pruning excess foliage. Although flooding may promote the spread of Phytophthora , anoxia is more likely to kill roots over the short term than Phytophthora .  Over the longer term, prolonged flooding events can weaken roots and elevate the activity of Phytophthora after draining.  Therefore, when fibrous roots are regenerating it is essential to minimize water stress (drought or excess) by monitoring irrigation frequency and duration and measuring water table fluctuations in the root zone with monitoring wells. Fungicide treatments to control Phytophthora root rot should be based on soil and root propagule counts.  2004 Florida Citrus Pest Management Guide: Phytophthora Foot Rot and Root Rot ,  J.H. Graham and L.W. Timmer
Drainage
More information on tree flood damage can be found at Drainage Systems for Flatwoods Citrus in Florida.    by Brian Boman and Dave Tucker. 2002. http://edis.ifas.ufl.edu/CH165

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